Ask the Experts: COVID-19

This page was last updated on March 19, 2024. See CDC’s Use of COVID-19 Vaccines in the United States Interim Clinical Considerations for more information. For a comprehensive collection of COVID-19 tools and resources, visit Immunize.org’s Vaccines: COVID-19 main page: www.immunize.org/covid-19. For alerts about new Immunize.org or CDC COVID-19 resources, subscribe to our weekly e-newsletter, IZ Express.

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COVID-19 is the name given to the disease caused by infection with the SARS-CoV-2 coronavirus. This virus was first detected as a cause of human illness in late 2019 in Wuhan, China, and triggered a global pandemic that began in 2020. The virus is thought to spread mainly from person to person through respiratory droplets and small particles produced when an infected person coughs, sneezes, or talks. The virus spreads easily in crowded or poorly ventilated indoor settings. Some people who are infected have no symptoms of illness, while the severity of symptomatic illness ranges from mild to life-threatening. Older adults and people of any age with underlying medical conditions are at higher risk for severe illness.

The incubation period after exposure ranges from 2–14 days, with an average of about 5 days. People with COVID-19 are generally considered potentially infectious up to 48 hours before symptom onset through 10 days after onset, though people with severe illness may be infectious longer. Symptoms may include fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, and diarrhea.

Last reviewed: March 19, 2024

The CDC has assembled clinical information about COVID-19 at this site: www.cdc.gov/coronavirus/2019-nCoV/hcp/index.html.

Last reviewed: March 19, 2024

CDC maintains a webpage with critical interim clinical considerations for vaccination of eligible recipients: www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html. This covers important clinical details about COVID-19 vaccination. It is the first content to be updated soon after any announced change to CDC recommendations.

All of the CDC’s Advisory Committee on Immunization Practices (ACIP) vaccine recommendations published in MMWR can be accessed here: www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/covid-19.html.

CDC has created infographic documents with the current recommended COVID-19 vaccination schedules for each age group:

Last reviewed: March 19, 2024

All people age 6 months and older in the United States are recommended to receive an age-appropriate updated (2023–2024 Formula) COVID-19 vaccination. Schedules vary by age and immunocompromised status. CDC has created infographic documents with the current recommended COVID-19 vaccination schedules for each age group:

Last reviewed: March 19, 2024

CDC recommends that all people receive an updated (2023–2024 Formula) COVID-19 vaccine, as authorized or approved by FDA. There are three options: Moderna or Pfizer-BioNTech mRNA vaccine (both FDA-authorized beginning at age 6 months and FDA-licensed for age 12 years and older), or Novavax adjuvanted protein subunit vaccine (authorized for age 12 years or older). Most people age 5 years through 64 years should receive a single dose of vaccine.

Certain people need, or have the option to receive, more than one 2023–2024 COVID-19 vaccine dose:

  • All adults age 65 years and older should receive a second dose of any 2023–2024 Formula COVID-19 vaccine at least 4 months after receiving their first dose of 2023–2024 Formula COVID-19 vaccine. The first and second doses do not need to be the same brand. If administering Novavax to a previously unvaccinated person in this age group, administer the recommended 2-dose primary series, followed by a third dose of 2023–2024 COVID-19 vaccine at least 4 months after completing the 2-dose primary series.
  • All previously unvaccinated individuals age 12 years or older receiving Novavax vaccine should receive two doses separated by at least 3 weeks. If age 65 years or older and previously unvaccinated, administer the 2-dose primary series, followed by a third dose of 2023–2024 COVID-19 vaccine at least 4 months after completing the 2-dose primary series.
  • Children younger than age 5 years are recommended to receive at least one updated 2023–2024 Formula mRNA vaccine dose. If not previously vaccinated, or incompletely vaccinated, they should complete a 2-dose (Moderna) or 3-dose (Pfizer-BioNTech) primary series, using the same brand for all doses. CDC recommends that children younger than age 5 years receive the same brand for all doses (also referred to as homologous doses), even after completing the primary series. If it is not feasible to administer the same brand for one of the following reasons, it is acceptable to use a different brand: the brand is unavailable at the clinic at the time of the vaccination visit; the previous brand is unknown; the child would not otherwise receive a recommended vaccine; or, the child cannot continue with the previous brand due to a contraindication.
  • Individuals who are moderately or severely immunocompromised and who have not already completed a 3-dose primary series, should complete a 3-dose primary vaccination series with the updated 2023–2024 Formula. Use the same brand for all doses of the primary series, unless the brand is unavailable at the time of the clinic visit, the patient would otherwise choose not to complete the series, or the patient has a contraindication to vaccination with the original product. If the primary series is already complete, then a single dose of any age-appropriate updated (2023–2024 Formula) COVID-19 vaccine should be administered at least 2 months after the most recent dose of COVID-19 vaccine. Additional doses may be given, spaced at least 2 months apart, as determined by these individuals with their clinical teams.

CDC has created infographic documents with the current recommended COVID-19 vaccination schedules for each age group:

Last reviewed: March 19, 2024

For individuals with moderate to severe immunocompromise, CDC states that, beyond the primary series, additional doses of 2023–2024 COVID-19 vaccine may be administered (with a minimum two-month interval) based on the clinical judgment of the individual’s healthcare provider and personal preference and circumstances.

The option to receive these additional doses is offered because vaccine effectiveness declines most rapidly in people with moderate to severe immunocompromise. Such people also have the highest risk of hospitalization with COVID-19 if infected. Although protection against severe disease is more durable than protection against milder illness, individuals in these groups may benefit from shorter intervals between doses.

CDC has created infographic documents with the current recommended COVID-19 vaccination schedules for immunocompromised people in each age group. See “Recommended updated (2023–2024 Formula) COVID-19 vaccines for people who ARE moderately or severely immunocompromised”: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf

Last reviewed: March 19, 2024

Janssen (Johnson & Johnson) COVID-19 vaccine is no longer available for use in the United States. The last remaining doses expired May 7, 2023. People age 18 years or older who received 1 or 2 Janssen COVID-19 Vaccine doses are recommended to receive one 2023–2024 Formula dose (Moderna, Pfizer-BioNTech, or Novavax). If age 65 years or older, a second 2023–2024 Formula dose of any brand should be given at least 4 months following the first 2023–2024 Formula dose.

Last reviewed: March 19, 2024

Yes. Vaccination should be offered regardless of history of prior SARS-CoV-2 infection.

Viral testing to assess for current SARS-CoV-2 infection or serologic testing to assess for prior infection for the purposes of vaccine decision-making is not recommended. However, as with all vaccines, vaccination should be deferred until after recovery from moderate to severe illness. In addition, to minimize the risk of exposing others to SARS-CoV-2 virus, vaccination of a person diagnosed with COVID-19 generally should be deferred until the person does not pose a risk of infection to others.

Although not required, people who recently had SARS-CoV-2 infection may consider delaying a 2023–2024 COVID-19 vaccine dose by up to 3 months from symptom onset or positive test (if infection was asymptomatic). Among vaccine recipients at increased risk of post-vaccination myocarditis (e.g., adolescent and adult males younger than age 40), an increased interval may reduce the rare risk of myocarditis after vaccination. A recipient’s individual risks for severe disease and current COVID-19 conditions in the community should be taken into account when deciding whether to delay vaccination up to 3 months after infection.

Last reviewed: March 19, 2024

CDC defines an “additional primary dose” as a subsequent dose of vaccine administered to people who are less likely to develop a protective immune response after initial vaccination because of moderate or severe immunocompromise. All previously unvaccinated people with moderate or severe immunocompromise are recommended to receive an initial 3-dose primary COVID-19 series.

CDC defines a “booster dose” as a subsequent dose of vaccine administered to enhance or restore protection which might have declined over time after primary series vaccination.

Last reviewed: March 19, 2024

Under section 564 of the Federal Food, Drug, and Cosmetic Act (FD&C Act), the FDA Commissioner may allow unapproved medical products or unapproved uses of approved medical products to be used in an emergency to diagnose, treat, or prevent serious or life-threatening diseases or conditions caused by chemical, biological, radiological or nuclear threat agents when there are no adequate, approved, and available alternatives. Vaccines that receive an EUA may later be fully licensed by the FDA.

Last reviewed: March 19, 2024

No. Only the updated (2023–2024 Formula) COVID-19 vaccines are currently authorized or approved for use in the United States.

Last reviewed: March 19, 2024

Moderna COVID-19 Vaccine has two updated (2023–2024 Formula) presentations. CDC has summarized basic information about the different presentations and their storage, preparation, and administration in its Moderna COVID-19 vaccine at-a-glance document available here: www.cdc.gov/vaccines/covid-19/info-by-product/moderna/downloads/vaccine-at-a-glance.pdf.

Vaccinators who stock multiple presentations should check three times to confirm that they are administering the proper product with the proper dose and dose volume for each patient.

Last reviewed: March 19, 2024

Both the Pfizer-BioNTech COVID-19 Vaccine and the Moderna COVID-19 Vaccine are lipid nanoparticle-formulated, nucleoside-modified mRNA vaccines encoding the prefusion spike glycoprotein of SARS-CoV-2, the virus that causes COVID-19. The 2023–2024 formula targets the Omicron XBB.1.5 sublineage of the spike protein. Visit this CDC website for more details about how mRNA vaccines work: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/how-they-work.html.

Last reviewed: March 19, 2024

The original COVID-19 vaccines all targeted the spike protein of the original SARS-CoV-2 virus. The current vaccines target the spike protein of a more recently circulating strain, known as the Omicron XBB.1.5 sublineage. The update is intended to boost production of antibodies that protect more effectively against disease caused by currently circulating Omicron subvariants.

The process of updating the strain without changing anything else is similar to the seasonal strain changes made for influenza vaccinations each year; FDA does not require manufacturers to repeat the large-scale clinical trials necessary for the original products before authorizing updated vaccines. Vaccine safety, side effects, and risk of allergic reactions are expected to be comparable to the original vaccines of the same brand and dose. As with seasonal influenza vaccines, future COVID-19 vaccines can continue to be updated when needed, as the circulating viruses evolve.

Last reviewed: March 19, 2024

No. The last U.S. doses of Janssen COVID-19 Vaccine expired May 7, 2023.

Last reviewed: March 19, 2024

Novavax COVID-19 Vaccine, Adjuvanted contains the Omicron XBB.1.5 subvariant SARS-CoV-2 spike protein and Matrix-M adjuvant. The saponin-based adjuvant is made from extracts of the bark of the Soapbark tree native to Chile. It is added to enhance the immune response of the vaccine recipient. The spike protein is produced in insect cells.

It is authorized for emergency use in people age 12 years or older as a two-dose primary series for previously unvaccinated individuals (whether or not they are immunocompromised), with the doses given at least 3 to 8 weeks apart. Individuals who have had one or more doses of any previous authorized or approved COVID-19 vaccine formulation are recommended to receive only one dose of the current formulation. An additional dose of Novavax or any other COVID-19 vaccine is recommended for adults age 65 years or older at least 4 months after their first dose of the 2023-2024 Formula COVID-19 vaccine. Individuals with moderate or severe immunocompromise may receive additional doses as determined by their healthcare team, based on their specific circumstances.

Last reviewed: March 19, 2024

The effectiveness of Novavax COVID-19 Vaccine against currently circulating variants of SARS-CoV-2 is not precisely known. Clinical trials of this vaccine were conducted against earlier variants no longer in circulation; however, the vaccine showed very good effectiveness against moderate to severe disease during clinical trials. Testing conducted on antibodies in the serum of Novavax vaccine recipients suggests that vaccination provides substantial protection against severe disease and death caused by currently circulating variants, consistent with other available COVID-19 vaccines.

Last reviewed: March 19, 2024

CDC has developed a “one-stop” product-specific webpage for each COVID-19 vaccine with all of the important details that immunization providers need to know: www.cdc.gov/vaccines/covid-19/info-by-product/index.html.

Last reviewed: March 19, 2024

All children age 6 months and older should be vaccinated against COVID-19 with at least one dose of an updated (2023–2024) formulation vaccine. COVID-19 vaccination of children in this age group has been demonstrated to be safe and to prevent hospitalization and severe complications of COVID-19 illness. Both Pfizer-BioNTech and Moderna mRNA products are authorized for use in children down to 6 months of age. Novavax adjuvanted protein subunit vaccine is authorized for use beginning at age 12 years.

Most children younger than age 5 years initially require a primary series of two (Moderna) or three (Pfizer-BioNTech) doses of the same brand. The primary series may include doses of previously authorized formulations. CDC recommends use of the same brand (referred to as homologous doses) for all recommended doses given to children younger than age 5 years. If it is not possible to administer a homologous dose (the brand is unavailable at the time and location of the vaccination visit, the brand of a previous dose is unknown, the child would not be vaccinated with the homologous dose due to a contraindication or other reason), then administer the age-appropriate formulation of the available brand. A 3-dose primary series is required for all children and adults who have moderate or severe immunocompromise.

CDC has prepared infographics to make it easier to determine exactly what vaccination is due for each patient, based upon the patient’s age, vaccination history, and immunocompromised status. For most children younger than age 12 years, see this CDC infographic: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-most-people.pdf.

For children younger than 12 years who are moderately or severely immunocompromised, see this CDC infographic: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

Last reviewed: March 19, 2024

This child should receive the dose recommended for his age at the time of the vaccination visit. At age 11 years, an age-appropriate single dose of either Pfizer-BioNTech or Moderna mRNA vaccine is recommended. If the patient arrives in your clinic after turning 12 years old, the 2023-2024 Formula Novavax protein subunit vaccine is also an option. If using the Novavax product, a previously unvaccinated person requires two doses, given 3 to 8 weeks apart, as a primary series.

Last reviewed: March 19, 2024

CDC states (www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#timing-spacing-interchangeability) that a person who moves to an older age group between vaccine doses should receive the vaccine product and dosage for the older age group for all subsequent doses.

Children who initiated their primary series with Pfizer-BioNTech brand products and turn age 5 years during the primary series have two options:

  1. Receive a single dose of updated (2023–2024 Formula) Pfizer-BioNTech COVID-19 Vaccine, 0.3 mL/10 mcg (blue cap; blue label) on or after turning age 5 years. If the 10-mcg dose is the second dose, administer 3–8 weeks after the first dose; if it is the third dose, administer at least 8 weeks after the second dose, OR
  2. Complete the 3-dose series with updated (2023–2024 Formula) Pfizer-BioNTech COVID-19 Vaccine for ages 6 months–4 years, 0.3 mL/3 mcg (yellow cap; yellow label), as outlined in the FDA EUA.
Last reviewed: March 19, 2024

Children who initiate the Moderna 2-dose vaccination series at age 4 years and turn 5 years-old before receiving the second dose should receive the second dose in the series (no dose change is needed). See www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#timing-spacing-interchangeability.

Last reviewed: March 19, 2024

CDC states (www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#timing-spacing-interchangeability) that if a person moves to an older age group between vaccine doses, they should receive the vaccine product and dosage for the older age group for all subsequent doses. Thus, CDC’s general recommendation in this case is to complete the primary series with the dose appropriate for a child age 12 years.

In the case of immunocompromised children who initiate the primary series before turning 12 years old and need to complete the primary series after turning 12, the FDA EUA also permits completing the entire 3-dose series with the formula authorized for children ages 5 through 11 years.

Last reviewed: March 19, 2024

Both vaccines have been demonstrated to be safe, with side effects typical of those in older age groups. The most common local reaction in this age group is pain at the injection site; the most common systemic symptom in older children was fatigue and in younger children (6 through 23 months) irritability/crying and sleepiness were most common. Fever may occur after either vaccination. Febrile seizures can occur in infants and young children ages 6 months through 5 years as a result of any condition that causes a fever (most common with high fevers). Febrile seizures are uncommon after vaccination. Febrile seizures were rare after mRNA COVID-19 vaccine clinical trials in this age group, and CDC continues to monitor for this adverse event following vaccination in infants and young children.

No cases of myocarditis were reported during the clinical trials for either vaccine. To date, post-authorization surveillance has not detected an increased risk for myocarditis and pericarditis following mRNA COVID-19 vaccination in children ages 6 months–4 years (Pfizer-BioNTech) and ages 6 months–5 years (Moderna).

Last reviewed: March 19, 2024

Pfizer-BioNTech COVID-19 Vaccine (2023–2024 Formula), brand name Comirnaty, is FDA-licensed for a single dose in recipients age 12 years and older.

Moderna COVID-19 Vaccine (2023–2024 Formula), brand name Spikevax, is licensed for use in recipients age 12 years and older.

Novavax COVID-19 Vaccine (2023–2024 Formula) is authorized for emergency use as a 2-dose primary series or a single dose in previously vaccinated individuals age 12 years and older.

Last reviewed: March 19, 2024

Clinical trial results for the original monovalent Pfizer-BioNTech COVID-19 Vaccine (administered as a two-dose primary series) demonstrated that among vaccine recipients age 12–15 years, side effects during the 7 days after vaccination were commonly reported (90.9% of vaccine recipients reported a local reaction and 90.7% reported a systemic reaction). Most reactions were mild to moderate. Pain at the injection site was the most common local reaction. One in 10 reported a side effect that interfered with daily activities. Side effects usually resolved after 1–2 days. Systemic side effects (e.g., fever, fatigue, headache, muscle pain) were more commonly reported after the second dose than after the first dose. No specific safety concerns were identified among adolescent vaccine recipients.

The safety and side effects of the 2023–2024 formula mRNA vaccine introduced in September 2023 are expected to be consistent with the previous formulations of the product.

Last reviewed: March 19, 2024

Yes. The 2023–2024 formula Novavax vaccine is an option for any person age 12 years or older who is unvaccinated or was previously vaccinated with any COVID-19 vaccine and is due for a 2023–2024 updated vaccination. Any person age 12 years or older who has never had a dose of COVID-19 vaccine should receive two doses of Novavax vaccine, administered 3 to 8 weeks apart as a primary series.

Adults age 65 years or older who are not immunocompromised and who did not require a 2-dose primary series with the current 2023–2024 Formula are recommended to receive one additional dose of the current 2023–2024 Formula at least 4 months after the first 2023–2024 Formula dose; those who did require a 2-dose primary series this season should get a third dose at least 4 months following completion of the primary series.

Novavax recipients with moderate to severe immunocompromise being vaccinated for the first time may receive a third dose at least 2 months following the second dose in their primary series and may receive subsequent additional doses at the discretion of their healthcare provider, in consideration of their individual circumstances.

Additional details from FDA are available: www.fda.gov/vaccines-blood-biologics/coronavirus-covid-19-cber-regulated-biologics/novavax-covid-19-vaccine-adjuvanted.

Last reviewed: March 19, 2024

Yes. Evidence continues to demonstrate that COVID-19 vaccination is safe and effective during any stage of pregnancy; the benefits of vaccination clearly outweigh any known or potential risks of COVID-19 vaccination during pregnancy. The currently licensed or authorized COVID-19 vaccines are non-replicating vaccines and cannot cause infection in either the pregnant person or the fetus. No evidence exists of risk to the fetus from vaccinating pregnant people with non-replicating vaccines in general.

Data from the Vaccine Adverse Events Reporting System (VAERS), the V-safe surveillance system, and the V-safe pregnancy registry have not signaled any safety concerns for pregnant people who were vaccinated or their infants. The vaccine manufacturers are following the pregnancy outcomes of people in the clinical trials who became pregnant. Additional studies in pregnant people are ongoing in order to fully evaluate pregnancy and birth outcomes.

All people who are pregnant are recommended to receive an updated (2023–2024 Formula) COVID-19 vaccine, as licensed or authorized by FDA, if they have not already received one.

Last reviewed: March 19, 2024

Yes. COVID-19 vaccination is recommended for all people who are not up to date, including those who are pregnant or lactating. Pregnant people are at increased risk of severe complications and death from COVID-19 compared to non-pregnant people of the same age. Those who contract COVID-19 during pregnancy also have almost twice the risk of stillbirth compared to those who do not contract COVID-19 during pregnancy. Studies have shown that antibodies produced after COVID-19 vaccination during pregnancy are transferred to the newborn, and COVID-19 vaccination of people who are pregnant reduces the risk of COVID-19 hospitalization in infants younger than 6 months. Pregnant people should receive any licensed or authorized updated 2023–2024 Formula COVID-19 vaccine during pregnancy, as licensed or authorized by FDA.

There is no recommendation from CDC for COVID-19 vaccination during every pregnancy; therefore, at this time, a person who is up to date on COVID-19 vaccination and becomes pregnant is not recommended to get an additional dose.

CDC, the American College of Obstetricians and Gynecologists (ACOG), and the Society for Maternal-Fetal Medicine (SMFM) all recommend vaccination, when indicated, of pregnant people at any stage of pregnancy.

For more details about COVID-19 vaccination during pregnancy, visit CDC’s webpage, “COVID-19 Vaccines while Pregnant or Breastfeeding”: www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/pregnancy.html.

Last reviewed: March 19, 2024

Yes. COVID-19 vaccination is recommended for people who are lactating.

Last reviewed: March 19, 2024

Please see CDC’s Interim Clinical Considerations for the Use of COVID-19 Vaccines for dosage guidance: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised..

People who are moderately or severely immunocompromised, who have not been vaccinated against COVID-19 in the past, and who are receiving the 2023–2024 Formula Novavax COVID-19 Vaccine should receive 2 doses spaced 3 to 8 weeks apart. They may receive a third dose at least 2 months after dose 2. As with mRNA COVID-19 vaccine recipients, they may receive additional doses at the discretion of their healthcare provider, based on their individual circumstances. CDC recommends that any additional doses be administered at least 2 months after the most recent 2023–2024 Formula dose.

Immunocompromised people should be counseled that they may have a reduced immune response to COVID-19 vaccination. They should be advised to continue other recommended infection prevention measures, such as wearing a face mask and avoiding crowds, to limit their risk of exposure to the SARS-CoV-2 virus.

Last reviewed: March 19, 2024

The conditions and treatments that CDC specifies may result in moderate or severe immunocompromise include but are not limited to:

  • Active treatment for solid tumor and hematologic malignancies
  • Hematologic malignancies associated with poor responses to COVID-19 vaccines regardless of current treatment status (e.g., chronic lymphocytic leukemia, non-Hodgkin lymphoma, multiple myeloma, acute leukemia)
  • Receipt of solid-organ transplant or an islet transplant and taking immunosuppressive therapy
  • Receipt of chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic cell transplant (HCT) (within 2 years of transplantation or taking immunosuppressive therapy)
  • Moderate or severe primary immunodeficiency (e.g., common variable immunodeficiency disease, severe combined immunodeficiency, DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced HIV infection (people with HIV and CD4 cell counts less than 200/mm³, history of an AIDS-defining illness without immune reconstitution, or clinical manifestations of symptomatic HIV) or untreated HIV infection
  • Active treatment with high-dose corticosteroids (i.e., 20 mg or more of prednisone or equivalent per day when administered for 2 or more weeks), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor necrosis factor (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory (e.g., B-cell-depleting agents)

Additional factors to consider in assessing the general level of immune competence in a patient include disease severity, duration, clinical stability, complications, comorbidities, and any potentially immune-suppressing treatment. A patient’s clinical care team is in the best position to evaluate the degree of immunocompromise and timing of vaccination.

See CDC’s interim clinical considerations for this population: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised.

Last reviewed: March 19, 2024

Yes. See all information about vaccination of immunocompromised people, including revaccination considerations after HCT and for those on B-cell depleting therapies, at www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised. This is the most current statement from CDC on COVID-19 vaccination after HCT:

Recipients of HCT or CAR-T-cell therapy who received 1 or more doses of COVID-19 vaccine prior to or during treatment should be revaccinated. Revaccination should start at least 3 months (12 weeks) after transplant or CAR-T-cell therapy and should follow the currently recommended schedule for immunocompromised people who are unvaccinated.

A patient’s clinical team is best positioned to determine the degree of immune compromise, need for revaccination, and appropriate timing of revaccination.

Last reviewed: March 19, 2024

According to CDC’s interim clinical considerations for the use of COVID-19 vaccines, whenever possible, COVID-19 vaccines should be administered at least 2 weeks before initiation or resumption of immunosuppressive therapies. For patients who receive B-cell-depleting therapies on a continuing basis, COVID-19 vaccines should be administered approximately 4 weeks before the next scheduled therapy.

CDC also notes that timing of COVID-19 vaccination should take into consideration current or planned immunosuppressive therapies, optimization of both the patient’s medical condition and response to vaccination, and individual benefits and risks. Review the CDC’s considerations for COVID-19 vaccination of those on immunosuppressive therapies here: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#considerations-timing-COVID-19-vaccination-immunosuppressive-therapies.

Last reviewed: March 19, 2024

CDC states that no additional medical documentation is required before vaccination. People may simply affirm that they are moderately or severely immunocompromised and receive COVID-19 vaccine doses wherever vaccines are offered. Vaccinators should not deny COVID-19 vaccination to a person due to lack of documentation.

Last reviewed: March 19, 2024

Immunocompromised people who require an initial series of 3 doses of mRNA COVID-19 vaccine or two doses of Novavax COVID-19 vaccine should receive the initial series using the same brand, unless it is not feasible. If the same brand (referred to as a homologous dose) cannot be used for all primary series doses (e.g., the brand is unavailable at the time of the vaccination visit, the previous brand is unknown, or the patient would not be vaccinated with the previous brand due to a contraindication or other reason), then administer another appropriate brand. CDC recommends homologous doses for all doses administered to children younger than age 5 years. If the immunocompromised recipient is age 5 years or older, once the initial series is complete, any appropriate brand may be used for subsequent doses. CDC provides additional information at: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#Interchangeability.

Last reviewed: March 19, 2024

Primary vaccination with the Janssen COVID-19 Vaccine requires only a single dose. People who received the Janssen COVID-19 Vaccine primary dose require only one updated (2023–2024 Formula) dose by Moderna, Pfizer-BioNTech, or Novavax to be up to date. People who are moderately or severely immunocompromised have the option to receive 1 additional updated 2023–2024 Formula COVID-19 vaccine dose at least 2 months later. Further additional dose(s) may be administered, informed by the clinical judgment of a healthcare provider and personal preference and circumstances. Any further additional doses should be administered at least 2 months after the last 2023–2024 Formula COVID-19 vaccine dose.

To evaluate an immunocompromised individual’s COVID-19 vaccine needs based upon the person’s age and COVID-19 vaccination history, use this infographic from CDC: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

Last reviewed: March 19, 2024

The patient should receive an updated 2023–2024 COVID-19 mRNA dose now, if feasible, of the same brand as the initial two doses, in order to complete the 3-dose primary mRNA vaccine series recommended for people with moderate or severe immunocompromise. Advise the patient that he has the option to receive additional 2023–2024 Formula COVID-19 doses of any brand (at least 2 months apart) as needed, based on his clinical circumstances.

To evaluate an immunocompromised individual’s COVID-19 vaccine needs based upon the person’s age and COVID-19 vaccination history, use this infographic from CDC: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

Last reviewed: March 19, 2024

Yes. CDC states that people ages 6 months and older who are moderately or severely immunocompromised have the option to receive 1 additional dose of COVID-19 vaccine at least 2 months following the last recommended 2023–2024 Formula COVID-19 vaccine dose. Further additional dose(s) may be administered, informed by the clinical judgement of the healthcare provider and personal preference and circumstances. Any further additional doses should be administered at least 2 months after the last 2023–2024 COVID-19 vaccine dose.

To evaluate an immunocompromised individual’s COVID-19 vaccine needs based upon the person’s age and COVID-19 vaccination history, use this infographic from CDC: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

Last reviewed: March 19, 2024

All COVID-19 vaccines are administered intramuscularly. Preparation details and dose volume vary by product.

Last reviewed: March 19, 2024

Yes. CDC has published an appendix to its interim clinical considerations for the use of COVID-19 vaccines to address a wide range of errors in vaccine administration. It includes a detailed table outlining actions to take after an error has occurred: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us-appendix.html#appendix-b.

Categories of errors covered in the CDC table include:

  • Site/route
  • Age
  • Product and dosage
  • Incorrect intervals
  • Interchanging product types when not recommended
  • Incorrect diluent (certain Pfizer-BioNTech formulations)
  • Use of diluent when not indicated

Ask the Experts refers our readers to this CDC table for the most current and comprehensive guidance on COVID-19 vaccine administration errors and how to manage them. For all vaccine administration errors the following steps are recommended: inform the patient of the error, report the error to VAERS (https://vaers.hhs.gov) unless CDC’s guidance states that the error does not need to be reported, evaluate why the error occurred, and implement strategies to prevent future errors.

Last reviewed: March 19, 2024

No. CDC does not recommend repeating the dose of any COVID-19 vaccine in circumstances where the dose is administered in an incorrect route or an incorrect site (i.e., not in the deltoid or anterolateral thigh). In the case of a subcutaneous injection, the patient should be advised of the possibility of self-limited local or systemic side effects.

Last reviewed: March 19, 2024

Periodically verify whether you are using the most current available documents by checking Immunize.org’s regularly updated Checklist of Current Versions of U.S. COVID-19 Vaccination Guidance and Clinic Support Tools: www.immunize.org/catg.d/p3130.pdf. This resource is updated at least monthly with the dates of the most currently available materials from CDC and FDA.

There is normally a delay between the public announcement of a change in COVID-19 vaccination recommendations and the release of updated CDC guidance documents that incorporate the change. Information is generally updated first on the CDC web page: Use of COVID-19 Vaccines in the United States (www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html).

Last reviewed: March 19, 2024

No. Simply administer the next dose that is currently recommended. To determine what is needed now based upon a person’s vaccination history, age, and immunocompromised status, refer to the CDC COVID-19 Vaccination Infographic (for most people): www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-most-people.pdf and the CDC COVID-19 Vaccination Infographic (for immunocompromised people): /www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

Last reviewed: March 19, 2024

No. People should not be routinely scheduled to receive a dose earlier than recommended. Schedulers should offer appointments beginning on the date of the recommended interval or later. CDC guidance allows for doses to be given up to 4 days before the recommended interval in order to avoid missed vaccination opportunities when a recipient unexpectedly arrives early and might not return on schedule.

Last reviewed: March 19, 2024

In this specific situation, CDC states that a child age 6 months–4 years who received 1 Moderna and 1 Pfizer-BioNTech COVID-19 vaccine dose for the first 2 doses of COVID-19 vaccine should receive a third dose of the 2023–2024 Formula of either Moderna or Pfizer-BioNTech COVID-19 vaccine at least 8 weeks after the second dose.

For all questions of brand interchangeability, please review CDC’s interim recommendations for COVID-19 vaccine administration errors and deviations: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us-appendix.html#appendix-b.

Last reviewed: March 19, 2024

A person who is not moderately or severely immunocompromised and has only ever received a single dose of Novavax COVID-19 vaccine may receive a single dose of any licensed or authorized COVID-19 (2023–2024 Formula) vaccine, including Novavax.

Last reviewed: March 19, 2024

Everyone age 6 months and older is recommended to receive at least one dose of updated (2023–2024 Formula) COVID-19 vaccine, regardless of past vaccination history. Any updated (2023–2024 Formula) COVID-19 vaccine received in another country that is listed for emergency use by the World Health Organization (WHO-EUL) or authorized or licensed for use by the FDA counts toward fulfilling this recommendation.

CDC has provided additional details based upon age and immunocompromised status at its website: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us-appendix.html#appendix-a.

A list of the vaccines that have already received WHO-EUL status is available here: https://extranet.who.int/prequal/vaccines/covid-19-vaccines-who-emergency-use-listing.

Last reviewed: March 19, 2024

This patient, like other adults, is considered up to date after receiving a single dose of updated (2023–2024 Formula) COVID-19 vaccine at least 8 weeks after his most recent COVID-19 vaccination.

Last reviewed: March 19, 2024

An asymptomatic person who is scheduled for COVID-19 vaccination and is exposed to SARS-CoV-2 virus may be vaccinated; however, COVID-19 vaccination after exposure is not recommended as post-exposure prophylaxis, so vaccination should not be expected to prevent illness caused by past exposure. A person who is currently sick with a respiratory virus should defer vaccination until at least the recovery from the acute illness, and consider additional measures to prevent spread, in accordance with current CDC guidance. Healthcare facilities may have specific policies in place to reduce the risk of spread of respiratory viruses to healthcare staff and other patients.

CDC summarizes its current guidance on respiratory viruses (updated March 2024) here: www.cdc.gov/respiratory-viruses/guidance/respiratory-virus-guidance.html.

People who recently had SARS-CoV-2 infection and are due for a COVID-19 vaccine may consider delaying the dose by up to 3 months from symptom onset or positive test (if infection was asymptomatic). According to CDC, increasing the time between infection and vaccination may result in an improved immune response to vaccination. At this time, there is evidence of a low risk of reinfection in the weeks following infection. A recipient’s individual risks for severe disease and current COVID-19 conditions in the community should be taken into account when deciding whether to delay vaccination up to 3 months after infection.

Last reviewed: March 19, 2024

Yes, COVID-19 vaccines and other routine vaccines, including influenza and RSV vaccines, may be coadministered on the same day, given in different syringes and at different anatomical sites. COVID-19 vaccines may also be given at any interval before or after any other vaccination.

Of note, there is no required minimum interval between receiving a dose of any COVID-19 vaccine and an orthopoxvirus vaccine, either Jynneos or ACAM2000 vaccine (e.g., for mpox prevention), regardless of which vaccine is administered first. However, use of Jynneos vaccine should be prioritized over ACAM2000 when co-administering a COVID-19 vaccine and an orthopoxvirus vaccine.

People, particularly adolescent or young adult males, who are recommended to be vaccinated against both mpox and COVID-19 might consider waiting 4 weeks between vaccines. This is because of the observed risk for myocarditis and pericarditis after receipt of ACAM2000 orthopoxvirus vaccine and COVID-19 vaccines, and the hypothetical risk for myocarditis and pericarditis after Jynneos vaccine. However, if a patient’s risk for mpox or severe disease due to COVID-19 is increased, administration of mpox and COVID-19 vaccines should not be delayed.

Additional information is available from CDC: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#timing-spacing-interchangeability.

Last reviewed: March 19, 2024

Your patient may choose to receive the vaccines at the same visit or separately, without regard to the timing interval. In general, when deciding whether to coadminister other vaccines with COVID-19 vaccine, you should consider whether the patient is behind or at risk of becoming behind on recommended vaccines, their risk of vaccine-preventable disease (e.g., during an outbreak or occupational exposures), and the reactogenicity profile of the vaccines.

When multiple vaccines are administered at a single visit, administer each injection in a different syringe and at a different injection site. For adolescents and adults, the deltoid muscle may be used for more than one injection, though injection sites should be at least one inch apart. It is generally preferable to administer reactogenic vaccines such as Shingrix and COVID-19 vaccine in different arms, if possible. If the patient prefers both injections in the same deltoid, that is also acceptable.

Immunize.org has developed a one-page guide to administering multiple intramuscular vaccinations to an adult at one visit: www.immunize.org/catg.d/p2030.pdf.

Last reviewed: March 19, 2024

The timing of CDC-recommended vaccination is unaffected by the receipt of COVID-19 monoclonal antibodies or convalescent plasma.

Last reviewed: March 19, 2024

Yes, they may be vaccinated with any FDA-licensed or FDA-authorized updated (2023–2024 Formula) COVID-19 vaccine (Moderna, Pfizer, or Novavax) as long as they do not have a contraindication to vaccination. Antibody testing is not recommended to assess for immunity to SARS-CoV-2 following COVID-19 vaccination.

Recipients should be counseled about the unknown and variable effectiveness of COVID-19 vaccination in immunocompromised populations and the potential for reduced immune responses. They may consider other practices to reduce their risk of infection. CDC has published additional information about respiratory virus prevention for people with weakened immune systems: www.cdc.gov/respiratory-viruses/risk-factors/weakened-immune-systems.html.

CDC has developed an infographic for use with patients who have moderate to severe immunocompromise when determining what updated (2023–2024 Formula) COVID-19 vaccine is due based on the individual’s age and past COVID-19 vaccination history: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

CDC provides detailed considerations for vaccination of people with moderate or severe immunocompromise here: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised.

Last reviewed: March 19, 2024

History of an anaphylactic reaction to a dose of mRNA COVID-19 vaccine is a contraindication to receipt of further doses of mRNA-type COVID-19 vaccines. However, a person with a contraindication to one type of COVID-19 vaccine (mRNA) may receive the alternative COVID-19 vaccine type (in this case, the adjuvanted protein subunit vaccine by Novavax) in the usual vaccination setting. CDC encourages consultation with an allergist-immunologist to provide expert evaluation of the original allergic reaction, and depending on the outcome of that evaluation, reassess whether administration of additional doses of the original vaccine type may be possible.

Last reviewed: March 19, 2024

This condition is not rare and is sometimes referred to as “COVID arm”. Future doses should be given as recommended. Individuals with only a delayed-onset local reaction (e.g., redness, induration, itching) around the injection site area after an mRNA vaccine dose do not have a contraindication or precaution to subsequent doses. Consider administering the next dose in the opposite arm, if possible.

These delayed-onset local reactions are sometimes quite large but are self-limited. It is not known whether individuals who experienced a delayed-onset injection site reaction after one dose will experience a similar reaction after future doses. These reactions are not believed to represent an increased risk for anaphylaxis after future doses.

Patients who experience “COVID arm” may take an antihistamine if it is itchy or a pain medication, such as acetaminophen or a non-steroidal anti-inflammatory (NSAID), if it is painful.

Last reviewed: March 19, 2024

Medications to reduce fever and pain (e.g., acetaminophen, non-steroidal anti-inflammatory drugs) may be taken to treat post-vaccination local or systemic symptoms, if medically appropriate. However, routine administration of such medications before vaccination is not recommended because information on the potential impact of such use on COVID-19 vaccine-induced antibody responses is not available at this time.

Administration of antihistamines before COVID-19 vaccination to prevent allergic reactions is not recommended. Antihistamines do not prevent anaphylaxis, and their use might mask cutaneous symptoms, which could delay diagnosis and management of anaphylaxis.

Last reviewed: March 19, 2024

The COVID-19 vaccines currently available in the United States (mRNA vaccines and the Novavax protein subunit vaccine) are not contraindicated in patients with a history of TTS. The Janssen COVID-19 vaccine associated with immune-mediated TTS in the United States is no longer available.

Last reviewed: March 19, 2024

According to CDC, MIS-C and MIS-A both include a dysregulated immune response to SARS-CoV-2 infection. Experts consider the benefits of vaccination to outweigh the theoretical risk of an MIS-like illness or the risk of myocarditis following COVID-19 vaccination in a person with a history of MIS-C or MIS-A if the person meets the following criteria: (1) they have clinically recovered, including return to baseline cardiac function; and (2) it has been at least 90 days since the diagnosis of MIS-C or MIS-A.

There are additional considerations for vaccination of those who do not meet these criteria. Refer to CDC’s detailed guidance for the most current clinical considerations for vaccination of children and adults who have experienced this syndrome following SARS-CoV-2 infection or who have experienced MIS-like illness following COVID-19 vaccination: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#covid19-vaccination-misc-misa.

Last reviewed: March 19, 2024

CDC guidance is that people who have a history of completely resolved myocarditis or pericarditis unrelated to COVID-19 vaccination (e.g., due to SARS-CoV-2 or other viruses) may receive any age-appropriate COVID-19 vaccine that is FDA-approved or FDA-authorized. “Complete resolution” includes resolution of symptoms attributed to myocarditis or pericarditis, as well as no evidence of ongoing heart inflammation or sequelae as determined by the person’s clinical team.

For people who have a history of myocarditis associated with MIS-C or MIS-A following SARS-CoV-2 infection, see CDC’s interim clinical considerations concerning COVID-19 vaccination and MIS-C and MIS-A: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#covid19-vaccination-misc-misa.

Complete and current clinical considerations for COVID-19 vaccination of patients with a history of myocarditis are available from CDC here: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#myocarditis-pericarditis.

For additional information about myocarditis and mRNA COVID-19 vaccines, visit www.cdc.gov/vaccines/covid-19/clinical-considerations/myocarditis.html.

Last reviewed: March 19, 2024

Development of myocarditis or pericarditis within 3 weeks after a dose of any COVID-19 vaccine is a precaution to a subsequent dose of any COVID-19 vaccine, and subsequent doses should generally be avoided. Under certain conditions, the clinical team may determine that benefits of vaccination outweigh risks. See CDC’s detailed guidance for additional information about these clinical considerations: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#myocarditis-pericarditis.

Last reviewed: March 19, 2024

People with a history of GBS can receive any currently recommended COVID-19 vaccine.

Last reviewed: March 19, 2024

Recipients of mRNA COVID-19 vaccines often experience local (e.g., pain, swelling, redness at the injection site, localized swollen lymph nodes in the armpit of the vaccinated arm) or systemic (e.g., fever, fatigue, headache, chills, body and joint aches) post-vaccination symptoms. Depending on vaccine product (Pfizer-BioNTech vs. Moderna), age group, and vaccine dose, in clinical trials, approximately 80–91% of vaccinated people develop at least one local symptom and 55–91% develop at least one systemic symptom following vaccination.

Most systemic post-vaccination symptoms are mild to moderate in severity, occur within the first three days of vaccination, and resolve within 1–3 days of onset.

Among children ages 6 months through 4 years (Pfizer-BioNTech) or 6 months through 5 years (Moderna), pain or tenderness at the injection site was the most frequent local reaction. The most common systemic symptom in older children was fatigue; in younger children (ages 6 through 23 months), irritability/crying and drowsiness/sleepiness were most common. Most systemic symptoms were mild to moderate in severity, typically began 1 to 2 days after vaccination, and resolved after 1 to 2 days.

Last reviewed: March 19, 2024

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