Ask the Experts: COVID-19

The COVID-19 questions were last reviewed on August 31, 2024. See CDC’s Use of COVID-19 Vaccines in the United States Interim Clinical Considerations for more information. To keep up with the current available COVID-19 resources from CDC, FDA, and Immunize.org, see Immunize.org’s Checklist of Current Versions of U.S. COVID-19 Vaccine Guidance and Clinic Support Tools, updated at least monthly. 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 spreads 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 and up to 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: August 31, 2024

The CDC has assembled clinical information about COVID-19 at this site: www.cdc.gov/covid/hcp.

Last reviewed: August 31, 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/acip-recs/hcp/vaccine-specific/covid-19.html.

CDC posts product-specific resources at this site: www.cdc.gov/vaccines/covid-19/info-by-product/index.html. It generally takes a few days or weeks following FDA approval of new products for CDC to release updated resources.

Last reviewed: August 31, 2024

All people age 6 months and older in the United States are recommended to receive an age-appropriate 2024–2025 Formula COVID-19 vaccination. Schedules vary by age and immunocompromised status. CDC’s interim clinical considerations for the use of COVID-19 vaccines in the United States has been updated to reflect the current ACIP recommendations: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#vaccination-schedule-overview.

Last reviewed: August 31, 2024

CDC recommends that all people age 6 months or older should be vaccinated with a 2024–2025 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 or older should receive a single dose of vaccine.

Certain people need, or have the option to receive, more than one 2024–2025 Formula COVID-19 vaccine dose:

  • If administering Novavax to a previously unvaccinated person age 12 years or older, administer a recommended 2-dose primary series, with doses 3-8 weeks apart.
  • Children younger than age 5 years are recommended to receive at least one 2024–2025 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 current 2024–2025 formulation. 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 2024–2025 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 care teams.

At this time, adults age 65 years and older who are not moderately or severely immunocompromised are recommended to receive only 1 dose of any 2024–2025 Formula COVID-19 vaccine. These adults are not currently recommended to receive a second dose 6 months after the first dose. ACIP will consider recommendations for revaccination in the future.

Last reviewed: August 31, 2024

For individuals with moderate to severe immunocompromise, CDC states that, beyond the primary series, additional doses of 2024–2025 Formula 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.

Last reviewed: August 31, 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 who received 1 or 2 Janssen COVID-19 Vaccine doses are recommended to receive one 2024–2025 Formula dose (Moderna, Pfizer-BioNTech, or Novavax).

Last reviewed: August 31, 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 2024–2025 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 (such as males age 12 through 39 years), 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: August 31, 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: August 31, 2024

ACIP has not made a routine recommendation for COVID-19 vaccination of older adults every 6 months. Although vaccine effectiveness against hospitalization in this age group wanes significantly by 6 months after vaccination, the ACIP recommendation made in February 2024 for adults in this age group to receive an additional dose of the 2023–2024 Formula COVID-19 vaccine was based upon conditions at the time and the expectation that COVID-19 would continue to circulate through the summer of 2024. ACIP will evaluate data and make a decision concerning an additional dose during the 2024-25 respiratory virus season as the season progresses.

Last reviewed: August 31, 2024

In general, CDC recommends waiting a minimum of 8 weeks (2 months) since the last 2023–2024 Formula COVID-19 vaccine to receive an age-appropriate 2024–2025 Formula COVID-19 vaccine.

Previously unvaccinated children age 6 months through 4 years are recommended to receive a 2-dose (Moderna) or 3-dose (Pfizer-BioNTech) primary series of COVID-19 vaccine. Previously unvaccinated moderately or severely immunocompromised people are recommended to receive a 3-dose primary series of mRNA COVID-19 vaccine (either product) or a 2-dose primary series of Novavax COVID-19 vaccine. Any previously unvaccinated person who receives Novavax COVID-19 vaccine should receive a 2-dose primary series, 3-8 weeks apart. If a person in one of these categories initiated their primary series with a 2023–2024 formula vaccine, they are recommended to follow the age-appropriate recommended schedule for completion of the primary series with the 2024–2025 formula of the same brand.

Last reviewed: August 31, 2024


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Last reviewed: May 9, 2023

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: August 31, 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 2024–2025 formula targets the Omicron variant KP.2 sublineage of the spike protein.  Visit this CDC website for more details about how mRNA vaccines work: www.cdc.gov/covid/vaccines/how-they-work.html.

Last reviewed: August 31, 2024

The original COVID-19 vaccines all targeted the spike protein of the original SARS-CoV-2 virus. The 2024–2025 formulation vaccines target the spike proteins of more recently circulating strains, known as the Omicron KP.2 (mRNA vaccines) or JN.1 (protein vaccine) strains. 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 earlier formulations of 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: August 31, 2024

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

Last reviewed: August 31, 2024

Novavax COVID-19 Vaccine, Adjuvanted contains the Omicron JN.1 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 2024–2025 formulation. An additional dose of 2024–2025 Novavax or any other COVID-19 vaccine is not recommended for adults age 65 years or older at this time. Individuals with moderate or severe immunocompromise may receive additional doses as determined by their healthcare team, based on their specific circumstances.

Last reviewed: August 31, 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: August 31, 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: August 31, 2024

All children age 6 months and older should be vaccinated against COVID-19 with at least one dose of the current 2024–2025 formulation mRNA 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.

Last reviewed: August 31, 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 2024–2025 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: August 31, 2024

CDC states 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 transition from age 4 years to age 5 years during the initial vaccination series should receive 1 dose of the 2024–2025 vaccine from the same manufacturer at the dosage authorized for children age 5–11 years on or after turning age 5 years.

Last reviewed: August 31, 2024

Children who transition from age 4 years to age 5 years during the initial vaccination series should receive 1 dose of vaccine from the same manufacturer at the dosage for children ages 5–11 years on or after turning age 5 years. This child should receive one dose of the 2024–2025 Moderna vaccine (no dose change is needed).

Last reviewed: August 31, 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 recommendation in this case is to complete the primary series with the dose appropriate for a child age 12 years. The option to continue the series after the child’s birthday with the dose recommended at the younger age is no longer recommended or authorized.

Last reviewed: August 31, 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: August 31, 2024


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Last reviewed: June 22, 2023

Pfizer-BioNTech COVID-19 Vaccine (2024–2025 Formula), brand name Comirnaty, is FDA-licensed for a single dose in recipients age 12 years and older.

Moderna COVID-19 Vaccine (2024–2025 Formula), brand name Spikevax, is licensed for use in recipients age 12 years and older.

Novavax COVID-19 Vaccine (2024–2025 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: August 31, 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 2024–2025 formula approved in August 2024 are expected to be consistent with the previous formulations of the product.

Last reviewed: August 31, 2024

Yes. The 2024–2025 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 2024–2025 updated vaccination. Any person age 12 years or older who has never had a dose of any 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 2024–2025 Formula are NOT recommended to receive any additional doses of the current 2024–2025 Formula at this time.

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: August 31, 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.

All people who are pregnant are recommended to receive a 2024–2025 Formula COVID-19 vaccine, as licensed or authorized by FDA, if they have not already received one.

Last reviewed: August 31, 2024

Yes. COVID-19 vaccination with a 2024–2025 Formula vaccine is recommended for all people age 6 months or older, 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 2024–2025 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, 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/covid/vaccines/pregnant-or-breastfeeding.html.

Last reviewed: August 31, 2024


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Last reviewed: April 6, 2023

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

Last reviewed: August 31, 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 2024–2025 Formula mRNA vaccines (Moderna or Pfizer) should receive a 3-dose primary series of age-appropriate doses of the same vaccine brand, unless obtaining the same brand is not feasible. A 4-week interval is recommended between doses 1 and 2 and doses 2 and 3. One additional dose may be administered at least 2 months following the final dose in the primary series. Further additional doses may be administered at least 2 months apart, based upon the judgment of the patient’s healthcare team and the patient’s preferences and circumstances.

People who are moderately or severely immunocompromised, who have not been vaccinated against COVID-19 in the past, and who are receiving the 2024–2025 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 team, based on their individual preferences and circumstances. CDC recommends that any additional doses be administered at least 2 months after the most recent 2024–2025 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.

Pemivibart (Pemgarda, Invyvid) is a monoclonal antibody for COVID-19 pre-exposure prophylaxis in people who are moderately or severely immunocompromised and unlikely to mount an adequate immune response to COVID-19 vaccination and who meet the FDA-authorized conditions for use. See additional information from CDC: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised.

Last reviewed: August 31, 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: August 31, 2024

Yes. See 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#considerations-COVID-19-revaccination. 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: August 31, 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: August 31, 2024

CDC states that no additional medical documentation is required before vaccination.  The patient’s affirmation of moderate or severe immunocompromise is sufficient: vaccinators should not deny COVID-19 vaccination to a person due to lack of documentation.

Last reviewed: August 31, 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: August 31, 2024

Primary vaccination with the Janssen COVID-19 Vaccine required only a single dose. People who received the Janssen COVID-19 Vaccine primary dose require only one 2024–2025 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 2024–2025 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 the recipient’s personal preference and circumstances. Any further additional doses should be administered at least 2 months after the last 2024–2025 Formula COVID-19 vaccine dose.

Last reviewed: August 31, 2024

The patient should receive a 2024–2025 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 2024–2025 Formula COVID-19 doses of any brand (at least 2 months apart) as needed, based on his clinical circumstances.

Last reviewed: August 31, 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 2024–2025 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 COVID-19 vaccine dose.

Last reviewed: August 31, 2024

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

Last reviewed: August 31, 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: August 31, 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: August 31, 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: August 31, 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’s overview of the vaccination schedule for the 2024–2025 COVID-19 vaccine formulation: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#vaccination-schedule-overview.

Last reviewed: August 31, 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: August 31, 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 2024–2025 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: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#Interchangeability.

Last reviewed: August 31, 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 2024–2025 Formula COVID-19 vaccine, including Novavax.

Last reviewed: August 31, 2024

Everyone age 6 months and older is recommended to receive at least one dose of 2024–2025 Formula COVID-19 vaccine, regardless of past vaccination history. Any 2024–2025 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: August 31, 2024

This patient, like other adults who are not moderately or severely immunocompromised, is considered up to date after receiving a single dose of 2024–2025 Formula COVID-19 vaccine at least 8 weeks after his most recent COVID-19 vaccination.

Last reviewed: August 31, 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: http://www.cdc.gov/respiratory-viruses/guidance/index.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: August 31, 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 about simultaneous administration with other vaccines is available from CDC: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#age-transitions.

Last reviewed: August 31, 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: August 31, 2024

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

Last reviewed: August 31, 2024

Yes, they may be vaccinated with any FDA-licensed or FDA-authorized 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 provides detailed considerations for vaccination and the use of pemivibart (Pemgarda, Invyvid) long-acting monoclonal antibody for pre-exposure prophylaxis in people with moderate or severe immunocompromise here: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised.

Last reviewed: August 31, 2024

Anaphylaxis occurs at a rate of approximately 5 cases per 1 million mRNA COVID-19 vaccinations administered. 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: August 31, 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: August 31, 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: August 31, 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: August 31, 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: August 31, 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: August 31, 2024

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