FAQs for the Interim Clinical Considerations

Vaccination Schedule and Use

Yes. For primary series vaccination Moderna, Pfizer-BioNTech, and Novavax COVID-19 vaccines are recommended. For booster vaccination, Moderna and Pfizer-BioNTech are recommended; recommendations for the booster dose vary based on age and primary series product. Janssen COVID-19 Vaccine should only be used in very limited situations.

For more information, see:

In general, all doses of the primary series should be with the same product.

In the following exceptional situations, a different, age-appropriate COVID-19 vaccine may be administered to complete a primary series at a minimum interval of 28 days from the last COVID-19 vaccine dose. No VAERS report is required:

  • The same vaccine is not available
  • The first dose is unknown
  • A person starts but is unable to complete a primary series with the same COVID-19 vaccine due to a contraindication.

For more information, see timing, spacing, and interchangeability of COVID-19 vaccines.

No. You should administer the second dose as close as possible to the recommended interval after the first dose. However, if the second dose is administered after this interval, there is no need to restart the series.

An 8-week interval may be optimal for some people, especially males ages 12–39 years because of the small risk of myocarditis and pericarditis associated with Moderna, Novavax, and Pfizer-BioNTech COVID-19 vaccines. Vaccine effectiveness may also be increased with an interval longer than 3 or 4 weeks.

For additional information on the vaccination schedule, see:

Yes. Doses administered up to 4 days before the minimum interval, known as the 4-day grace period, are considered valid. This applies to primary series and booster doses of vaccine. Do not use the grace period to schedule doses.

If a dose is administered earlier than the grace period, see Appendix D for guidance on corrective actions. A dose administered earlier than the grace period is considered a vaccine administration error; you are required to report COVID-19 vaccine administration errors to the Vaccine Adverse Event Reporting System (VAERS).

Doses administered at any time after the recommended interval are valid.

For more information, see timing, spacing, and interchangeability of COVID-19 vaccines.

In accordance with general best practices for immunizations, routine administration of all age-appropriate doses of vaccines simultaneously is recommended for children, adolescents, and adults for whom no specific contraindications exist at the time of the healthcare visit. This includes simultaneous administration of COVID-19 vaccine and other vaccines. However, there are additional considerations for Moderna, Novavax, and Pfizer-BioNTech COVID-19 vaccines if administering an orthopoxvirus vaccine.

For more information, see Coadministration of COVID-19 vaccines with other vaccines.

Yes. COVID-19 vaccination is recommended for everyone ages 6 months and older, including people with underlying medical conditions. COVID-19 vaccines are especially important for people with underlying medical conditions associated with higher risk for severe COVID-19.

As with other vaccines, you can vaccinate patients with a mild illness. A moderate or severe illness is a precaution to receiving any currently FDA-authorized or FDA-approved COVID-19 vaccine. It is not considered a contraindication. Generally, vaccination should be delayed until the acute illness has improved. However, if you and your patient believe the potential benefits of vaccination outweigh the potential risks, they may receive COVID-19 vaccine.

For more information, see General Best Practice Guidelines for Immunizations and contraindications and precautions for COVID-19 vaccination.

Vaccine Dosage and Formulation

Vaccine dosages are based on age and not size or weight because they work differently than other medications. This is true for COVID-19 vaccines and other routinely recommended vaccines, like influenza or hepatitis vaccines.

Medications are often based on weight because they are distributed through the bloodstream and work when a certain medication level is present. In this case, a person’s weight is important for the dosage. To achieve the same effects, a person weighing more will require more of a medication than a person weighing less.

Vaccines work differently and are not distributed through the bloodstream. Vaccines imitate an infection when administered, activating the body’s immune response, which typically occurs at or near the injection site. Immune cells are directed to the injection site to attack foreign cells or proteins and produce antibodies that travel throughout the body and will protect against future infection.

Because of how vaccines work, they typically require low quantities of active ingredients. Different dosages are evaluated during vaccine development to determine the lowest effective dose for the target age group. Clinical trials evaluate various dosing regimens to determine the best dosage and schedule that produces an adequate immune response which is both safe and effective.

For more information, see Understanding How Vaccines Work.

CDC recommends that people should receive the age-appropriate vaccine dosage based on their age on the day of vaccination. If a person moves from a younger age group to an older age group during the primary series or between the primary series and receipt of the booster dose, they should receive the vaccine dosage for the older age group for all subsequent doses.

However, Food and Drug Administration (FDA) authorization allows for different dosing for certain age transitions. For more information see:

If the incorrect formulation is administered

  • Resulting in a higher-than-authorized dose: Do not repeat dose.
  • Resulting in a lower-than-authorized dose: Repeat the dose immediately (no minimum interval) with the age-appropriate dose and formulation. Some experts suggest delaying the repeat dose for 8 weeks after the invalid dose based on the potential for increased reactogenicity and the rare risk of myocarditis and pericarditis associated with Moderna, Novavax, and Pfizer-BioNTech vaccines, especially in males ages 12-39 years. See Considerations for extended intervals for COVID-19 vaccine primary series.

If a person moves from a younger age group to an older age group during the primary series or between the primary series and booster dose, they should receive the vaccine dosage for the older age group for all subsequent doses. However, FDA allows the formulation for either age group to be administered for certain age transitions. See Moderna COVID-19 Vaccine for Children who Transition from a Younger to Older Age Group, Pfizer-BioNTech for Children who Transition from a Younger to Older Age Group, and the product-specific EUA for more information.

Booster Doses

Everyone ages 5 years and older who is eligible is recommended to receive 1 booster dose:

  • People ages 5−11 years who received Pfizer-BioNTech COVID-19 Vaccine primary series are recommend to receive 1 monovalent Pfizer-BioNTech COVID-19 Vaccine booster dose.
  • People ages 6−11 years who received Moderna COVID-19 Vaccine primary series are currently not eligible for any booster dose.
  • People ages 12 years and older who received a primary series, including those who received a monovalent booster dose(s), are recommended to receive 1 bivalent booster dose.

For more information on booster doses see schedules for:

For booster dose recommendations for people vaccinated outside the United States, see people who received COVID-19 vaccine outside the United States.

Bivalent booster dose: People ages 12 years and older who received a primary series with any COVID-19 vaccine, including people who previously received a monovalent booster dose(s), are recommended to receive 1 bivalent booster dose; any age-appropriate bivalent booster dose (Moderna or Pfizer-BioNTech) can be used.

Monovalent booster dose: People ages 5−11 years who received a Pfizer-BioNTech COVID-19 Vaccine primary series are recommended to receive 1 age-appropriate monovalent Pfizer-BioNTech COVID-19 Vaccine booster dose.

No booster dose: People ages 6−11 years who received Moderna COVID-19 Vaccine primary series and people ages 4 years and younger are not currently eligible for any booster dose.

For more information on booster doses, see

The bivalent booster dose is administered at least 2 months after completion of the primary series. The interval is the same regardless of which vaccine was administered for the primary series and which bivalent booster (Moderna or Pfizer-BioNTech) will be administered.

The bivalent booster dose is administered at least 2 months after the last monovalent booster dose.

Yes. Everyone ages 12 and older who completed a primary series is recommended to receive 1 bivalent booster dose regardless of previous booster dose history. For people who previously received 1 or more monovalent booster doses, the bivalent booster dose should be administered at least 2 months after the last monovalent booster dose.

Yes.  Everyone ages 12 years and older who completed a primary series is recommended to receive 1 bivalent booster dose, including people who previously received the recommended or more than the recommended number of monovalent booster doses. The bivalent booster dose should be administered at least 2 months after the last monovalent booster dose.

In general, you do not need to repeat the dose. However, providers may administer 1 bivalent booster dose as a repeat dose based on clinical judgement and patient preference. The repeat dose should be administered at least 2 months after the monovalent booster dose.

For more information, see vaccine administration errors and deviations.

Guidance to address this error varies by vaccine manufacturer:

Pfizer-BioNTech: If the patient received a bivalent booster dose instead of a monovalent primary series dose, do not repeat the dose. The primary and booster dosages are the same; the bivalent dose can be counted as a primary series dose.

Moderna: If the patient received a bivalent booster dose instead of a monovalent primary series dose, this is considered a lower-than-authorized dose. Repeat the dose with the correct monovalent product immediately (no minimum interval). Some experts suggest delaying the repeat dose for 8 weeks after the invalid dose based on the potential for increased reactogenicity and the rare risk of myocarditis and pericarditis from mRNA COVID-19 vaccine, especially in males ages 12–39 years.

Both situations are considered vaccine administration errors; you are required to report COVID-19 vaccine administration errors to the Vaccine Adverse Event Reporting System (VAERS).

For more information, see vaccine administration errors and deviations.

The current recommendation is for everyone who is eligible to receive 1 bivalent booster dose: this includes people who received the primary series but did not receive the previously recommended monovalent booster dose(s) and people who received 1 or 2 monovalent booster doses.  Because the guidance has changed, not everyone will receive the same number of booster doses.  However, once a person receives 1 bivalent booster dose, no additional booster doses are currently recommended.

Booster dose recommendations vary based on age and primary series product. A booster dose is currently authorized for:

  • Children ages 5–11 years who received a Pfizer-BioNTech primary series; 1 monovalent Pfizer-BioNTech booster dose is recommended.
  • Adolescents ages 12–17 years who received a Moderna, Novavax, or Pfizer-BioNTech primary series; 1 bivalent Pfizer-BioNTech booster dose is recommended.

A booster dose is currently not authorized for:

  • Children ages 6 months–11 years who received a Moderna primary series.
  • Children ages 6 months–4 years who received a Pfizer-BioNTech primary series.

Yes. The child should receive 1 monovalent booster dose when they turn age 5 years, and it has been at least 5 months since completing their primary series.

People who are Moderately or Severely Immunosuppressed

Yes. For COVID-19 vaccination guidance for people who are moderately or severely immunocompromised people, please refer to:

People can self-attest to their moderately or severely immunocompromised status and should be vaccinated according to the schedule for people who are moderately or severely immunocompromised.  Vaccinators and clinic administrators should not deny COVID-19 vaccination to a person because of a lack of documentation.

At this time, 3 doses are recommended for everyone ages 6 months–4 years who receives a primary series with Pfizer-BioNTech COVID-19 Vaccine regardless of immune status. As we learn more about the safety and efficacy of this COVID-19 vaccine in young children, additional primary doses may be authorized in the future.

At this time, 2 doses of Novavax are recommended for people who receive a primary series with Novavax regardless of immune status. As we learn more about the safety and efficacy of this COVID-19 vaccine, additional doses may be authorized in the future.

Yes. Everyone ages 12 years and older who completed a primary series is recommended to receive 1 bivalent booster dose regardless of previous booster dose history; this includes people who are moderately or severely immunocompromised. The bivalent booster dose should be administered at least 2 months after the last monovalent booster dose.

Patients who undergo HCT or CAR-T-cell therapy should be revaccinated for the monovalent primary series and bivalent booster dose received before or during treatment. There is no revaccination for monovalent booster dose(s).  After revaccination with the primary series, the patient should receive a bivalent booster dose.

Below are three scenarios and the recommended action:

If your patient received the primary series before or during treatment: Revaccinate the patient with the primary series and administer the bivalent booster dose at least 2 months after repeating the primary series.

If your patient received the primary series and 1 or 2 (or more) monovalent booster doses before or during treatment: Revaccinate the patient with the primary series. Do not revaccinate for the monovalent booster dose(s). The patient is recommended to receive a bivalent booster dose at least 2 months after repeating the primary series.

If your patient received the primary series and a bivalent booster dose before or during treatment: Revaccinate the patient with the primary series and the bivalent booster dose.

For more information, see considerations for COVID-19 revaccination.

Yes.  Administration of EVUSHELDTM should be deferred for at least two weeks after COVID-19 vaccination per the EVUSHELDTM EUA.  You can administer COVID-19 vaccine any time after receipt of EVUSHELDTM.

For all other passive antibody products for COVID-19, there is no deferral period between receipt of the product and COVID-19 vaccine administration.

For more information, see COVID-19 vaccination and EVUSHELD™ and CDC’s EVUSHELD™ guidance.

Yes. Everyone ages 12 years and older should get the COVID-19 vaccine primary series and 1 bivalent booster dose including people who are moderately or severely immunocompromised and receiving EVUSHELD™ for pre-exposure prophylaxis.

COVID-19 vaccines can be administered any time after receipt of EVUSHELD™. Administration of EVUSHELD™ should be deferred for at least 2 weeks after COVID-19 vaccination per the EVUSHELD EUA™.

For more information, see COVID-19 vaccination and EVUSHELD™ and CDC’s EVUSHELD™ guidance.

Yes. In addition to following the recommended COVID-19 vaccination schedule, EVUSHELD™ should be administered to people who are moderately or severely immunocompromised every 6 months to supplement vaccine protection.

Administration of EVUSHELD™ should be deferred for at least 2 weeks after COVID-19 vaccination per the EVUSHELD EUA™.  COVID-19 vaccines can be administered any time after receipt of EVUSHELD™.

For more information, see COVID-19 vaccination and EVUSHELD™ and CDC’s EVUSHELD™ guidance.

Vaccination and Laboratory Testing

Antibody testing is not currently recommended to assess the need for vaccination in an unvaccinated person or to assess immunity to SARS-CoV-2 following COVID-19 vaccination or after SARS-CoV-2 infection. Antibody tests for SARS-CoV-2 look for the presence of antibodies made in response to a previous infection or vaccination. Antibodies are an indicator of the body’s efforts to fight off the SARS-CoV-2 virus. None of the currently authorized SARS-CoV-2 antibody tests have been validated to evaluate specific immunity or protection from SARS-CoV-2 infection.

For assistance with patient counseling and education related to COVID-19 testing and vaccination, please see:

For more detailed information, please see: Interim Guidelines for COVID-19 Antibody Testing.

Vaccination and SARS-CoV-2 Infection

CDC recommends COVID-19 vaccination for all people ages 6 months and older, including people with a history of SARS-CoV-2 infection.

Prior infection: Offer vaccination regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection, including to people with prolonged post-COVID-19 symptoms and people who experienced SARS-CoV-2 infection (symptomatic or asymptomatic) after vaccination. People who recently had SARS-CoV-2 infection may consider delaying their primary or booster COVID-19 vaccine dose by 3 months from symptom onset or positive test (if infection was asymptomatic).

Current infection: Defer vaccination of people with known current SARS-CoV-2 infection until the person has recovered from acute illness (if the person has symptoms) and until criteria have been met for them to discontinue isolation.

Laboratory testing is not recommended for the purpose of vaccine decision-making.

For more information, see COVID-19 vaccination and SARS-CoV-2 infection.

COVID-19 Vaccine Safety

For information on contraindications and precautions to COVID-19 vaccination, see Contraindications and precautions.

Providers should consider observing all patients for 15 minutes after vaccination for syncope, per the Advisory Committee on Immunization Practices’ General Best Practice Guidelines.

Additionally, providers should consider observing people with the following medical histories for 30 minutes after COVID-19 vaccination to monitor for allergic reactions:

  • An allergy-related contraindication to a different type of COVID-19 vaccine.
  • Non-severe, immediate (onset within 4 hours) allergic reaction after a previous dose of COVID-19 vaccine.
  • Anaphylaxis after non-COVID-19 vaccines or injectable therapies.

For more information, see Post-vaccination observation period.

Considerations Involving Pregnancy, Lactation, and Fertility

Yes. CDC recommends COVID-19 vaccination for all people who are pregnant, breastfeeding, recently pregnant, trying to get pregnant now, or who might become pregnant in the future. mRNA and Novavax vaccines are recommended for all vaccine-eligible populations, including for people who are pregnant or lactating. Those who are considering receipt of the Janssen COVID-19 Vaccine should see Appendix A: Guidance for use of Janssen COVID-19 Vaccine.

For more information, see COVID-19 Vaccines While Pregnant or Breastfeeding.

Special Populations and Situations

In accordance with general best practices, preterm infants (infants born before 37 weeks’ gestation), regardless of birth weight, should receive COVID-19 vaccination at their chronological age and according to the same schedule and guidance as for full-term infants and children.

Infants of mothers who were vaccinated and/or had COVID-19 or SARS-CoV-2 infection before or during pregnancy should be vaccinated according to the recommended schedule.

People who previously received SARS-CoV-2 antibody products (anti-SARS-CoV-2 monoclonal antibodies or convalescent plasma) as part of COVID-19 treatment, post-exposure prophylaxis, or pre-exposure prophylaxis can be vaccinated at any time; COVID-19 vaccination does not need to be delayed following receipt of monoclonal antibodies or convalescent plasma.

However, people who are moderately or severely immunocompromised and received a COVID-19 vaccination should wait at least two weeks before receiving tixagevimab/cilgavimab (EVUSHELD™) for pre-exposure prophylaxis per the product EUA.

For more information, see COVID-19 vaccination and EVUSHELD™ and CDC’s EVUSHELD™ guidance.

Rare cases of Bell’s palsy (acute peripheral facial nerve palsy) were reported following vaccination of participants in mRNA COVID-19 vaccine clinical trials, but FDA was not able to determine whether these cases were causally related to vaccination.  People with a history of Bell’s palsy may receive any currently FDA-approved or FDA-authorized COVID-19 vaccine: mRNA (i.e., Moderna or Pfizer-BioNTech) and Novavax COVID-19 vaccines are recommended for the primary series and an age-appropriate mRNA vaccine is recommend for the booster dose.

For more information on the recommended vaccination, see COVID-19 vaccination schedule for people who are not moderately or severely immunocompromised.

GBS is a neurological disorder in which the body’s immune system damages nerve cells, causing muscle weakness and sometimes paralysis. For people with a history of GBS, as for the general population, mRNA (i.e., Moderna or Pfizer-BioNTech) and Novavax COVID-19 vaccines are recommended for the primary series, and an age-appropriate mRNA vaccine is recommended for the booster dose. No increased risk of GBS has been identified with receipt of mRNA COVID-19 vaccines.

See Guidance for use of Janssen COVID-19 Vaccine and Use of the Janssen (Johnson & Johnson) COVID-19 Vaccine for information on GBS and Janssen COVID-19 Vaccine for information on GBS and Janssen COVID-19 Vaccine.

For more information on the recommended vaccination, see COVID-19 vaccination schedule for people who are not moderately or severely immunocompromised.

Page last reviewed: September 27, 2022