Pfizer-BioNTech (COMIRNATY) COVID-19 Vaccine Questions

Below are answers to commonly asked clinical questions about Pfizer-BioNTech COVID-19 Vaccine. Get answers to other frequently asked questions:

Vaccination Schedule and Use

Yes. Second doses or additional primary doses of Pfizer-BioNTech COVID-19 Vaccine administered up to 4 days before the recommended date (4-day grace period) are considered valid. This means that the following are considered valid:

  • A second dose administered 17 or more days after the first dose
  • An additional primary dose administered 24 or more days after completion of the primary series (for moderately to severely immunocompromised people)

If a dose is inadvertently administered before the 4-day grace period, it should be repeated.

  • A second dose administered 16 or fewer days after the first dose should be repeated
  • An additional primary dose administered 23 or fewer days after completion of the primary series should be repeated

This is considered a vaccine administration error. Determine how the error occurred and implement strategies to prevent it from happening again. Additionally, you are required to report COVID-19 vaccine administration errors to the Vaccine Adverse Event Reporting System (VAERS).

If a patient received the first dose of an mRNA COVID-19 vaccine but is unable to complete the series with either the same or a different mRNA COVID-19 vaccine (e.g., due to contraindication), you may consider administering a single dose of Janssen COVID-19 Vaccine, with a minimum of 28 days between doses. Persons receiving Janssen COVID-19 Vaccine should be informed about the risk and symptoms of thrombosis with thrombocytopenia (TTS) and symptoms of TTS that could occur after vaccination (typically within 2 weeks).

For more information, see

Booster Doses

The 5-month interval is measured in calendar months, consistent with Advisory Committee on Immunization Practices’ General Best Practice Guidelines for Immunization. For example, if an eligible patient completed the second dose of their 2-dose primary series on April 1, 2021, they can receive a booster as soon as September 1, 2021.

People 12 through 17 years of age who have completed a mRNA primary COVID-19 vaccine series can only receive Pfizer-BioNTech COVID-19 Vaccine as a booster dose at this time.

People 18 years of age and older who have completed a primary COVID-19 vaccine series with any FDA-approved or FDA-authorized product have the option to receive any age-appropriate FDA-approved or FDA-authorized COVID-19 booster product (Pfizer-BioNTech, Moderna [0.25 mL dose], or Janssen), even if they were 18 years of age or younger at the time of the primary series. An mRNA COVID-19 vaccine is preferred over the Janssen COVID-19 Vaccine.

Learn more about considerations for selecting which booster dose to receive and considerations for Janssen COVID-19 Vaccine.

Yes, people 12 – 17 years of age may receive a Pfizer-BioNTech COVID-19 Vaccine booster dose if they mistakenly received any of the following as their primary series:

  • 1 dose Janssen COVID-19 Vaccine
  • 1 dose of Moderna and 1 dose of Pfizer-BioNTech COVID-19 Vaccine
  • 2 doses of Moderna COVID-19 Vaccine

Additional dose: People 5 years of age and older who are moderately or severely immunocompromised who received a 2-dose mRNA COVID-19 vaccine primary series should receive an additional primary dose of the same mRNA vaccine 28 days after the 2-dose series.

Booster dose: People 12 years of age and older who are moderately or severely immunocompromised should receive a booster dose at least 3 months after completing their additional primary dose.

People 12 through 17 years of age can only receive Pfizer-BioNTech COVID-19 Vaccine as a booster dose at this time.

People 18 years of age and older have the option to receive any FDA-approved or FDA-authorized COVID-19 vaccine; however, an mRNA vaccine is preferred over the Janssen COVID-19 Vaccine.

Vaccine Indications, Contraindications, and Precautions

Pfizer-BioNTech COVID-19 Vaccine and Risk of Myocarditis/Pericarditis

Yes. People who have a history of myocarditis or pericarditis unrelated to mRNA COVID-19 vaccination may receive any FDA-authorized or approved COVID-19 vaccine (mRNA vaccines are preferred) after the episode of myocarditis or pericarditis has completely resolved. This 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, which may include a cardiologist, and special testing to assess cardiac recovery.

No. Until additional safety data are available, experts advise that people who develop myocarditis or pericarditis after a first dose of an mRNA COVID-19 vaccine not receive a subsequent dose of any COVID-19 vaccine. People with a history of myocarditis or pericarditis who choose to receive a subsequent dose of an mRNA COVID-19 vaccine should wait at least until their initial episode of myocarditis or pericarditis has completely resolved. For men ages 18 years and older who choose to receive a subsequent dose of a COVID-19 vaccine, some experts advise that Janssen COVID-19 Vaccine be considered instead of an mRNA COVID-19 vaccine. However, these persons should be made aware that there is also a risk of TTS after Janssen vaccine in men in this age group. Decisions about proceeding with a subsequent dose of an mRNA vaccine should include a conversation between the patient, their parent, guardian, or caregiver (when relevant), and their clinical team.

Although myocarditis or pericarditis after mRNA COVID-19 vaccination can occur in both men and women, more cases have been reported in men in younger age groups. Consider myocarditis and pericarditis in adolescents or young adults with acute chest pain, shortness of breath, or palpitations. Ask about prior COVID-19 vaccination if you identify these symptoms, as well as relevant other medical, travel, and social history. For more information, please refer to Myocarditis and Pericarditis Following mRNA COVID-19 Vaccination.

Based on data from VAERS, confirmed cases have typically occurred within several days after COVID-19 vaccination.

Vaccine Storage and Handling

Contact the manufacturer about deviations from standard storage as described in the Fact Sheet for Healthcare Providers.  Let them know how long vaccine was stored at which temperature(s) so a determination can be made as to whether doses have been compromised. If the manufacturer does not have data to support the stability of the vaccine, repeat the dose immediately (no minimum interval).

This is considered a vaccine administration error. Determine how the error occurred and implement strategies to prevent it from happening again. Additionally, you are required to report COVID-19 vaccine administration errors to the Vaccine Adverse Event Reporting System.

Determining the expiration date is different for each formulation.

  • 5 through 11 years of age formulation (orange cap) and 12 years of age and older formulation (gray cap): Vaccine expires 9 months after the manufacture date.
    • The manufacture date is printed on the vial.
    • Count out 9 months, using the month printed on the vial as month 1.
    • The vaccine expires on the last day of the 9th month.
    • For example, if the date printed on the vial is 08/2021, month 1 is August 2021. Month 9 is April 2022. The vial expires April 30, 2022.
  • 12 years of age and older formulation (purple cap): Vaccine expires on the date printed on the vaccine vial.

For all formulations, as the expiration date approaches, contact the manufacturer to determine if it has been extended. Do not discard vaccine without ensuring the expiration date has passed.

Expired vaccine should NEVER be administered. To prevent this, use CDC’s COVID-19 Vaccine Expiration Date Tracking Tool.

Because of the ultra-cold storage requirements, the manufacturer recommends that you not open the vial tray and inspect individual vials. Rather, keep the trays closed and inspect only the outside of the package and trays. You may inspect vials when you are ready to thaw and use the vaccine.

If you have concerns about the condition of the package, contact the manufacturer.

Beyond-use date recommendations are based on formulation.

Track beyond-use dates for the 5 through 11 years of age formulation (orange cap):

  • Before mixing, vaccine may be stored in the refrigerator between 2°C and 8°C (36°F and 46°F) for up to 10 weeks. After 10 weeks, contact the manufacturer for guidance before discarding any vials.
  • Once mixed, vaccine must be discarded within 12 hours. Note: Some labels and cartons may state “Discard 6 hours after dilution.” The information in the Fact Sheet for Healthcare Providers supersedes the information on the label. The 12-hour beyond-use date is correct.

Track beyond-use dates for the 12 years of age and older formulation (purple cap):

  • Before mixing, vaccine may be stored in the refrigerator between 2°C and 8°C (36°F and 46°F) for up to 31 days. After 31 days, contact the manufacturer for guidance before discarding any vials.
  • Before mixing, vaccine may be stored in the freezer between -25°C and -15°C (-13°F to 5°F) for up to 2 weeks.
  • Once mixed, vaccine must be discarded within 6 hours.

Track beyond-use dates for the 12 years of age and older formulation (gray cap):

  • Before puncture, vaccine may be stored in the refrigerator between 2°C and 8°C (36°F and 46°F) for up to 10 weeks. The 10-week refrigerated expiry date should be recorded on the carton at the time of transfer. After 10 weeks, contact the manufacturer for guidance before discarding any vials.
  • Before first puncture, vaccine may be stored at room temperature [8°C to 25°C (46°F to 77°F)] for a total of 12 hours.
  • After the first puncture, the vial should be held between 2°C to 25°C (35°F to 77°F). Vials should be discarded 12 hours after first puncture. Note: Some vial labels and cartons may state “Discard 6 hours after first puncture.” The information in the Fact Sheet for Healthcare Providers supersedes the information on the label. The 12-hour beyond-use date is correct.

No. The beyond-use date replaces but never extends a manufacturer’s expiration date. In this case, 10 weeks would exceed the expiration of 1/31/22. As expiration date approaches, contact the manufacturer to determine if it has been extended. Do not discard vaccine without ensuring the expiration date has passed.

Yes. After the 2-week time frame, you have two options:

  • You may transfer vaccine to refrigerated storage between 2°C and 8°C (36°F and 46°F) for up to 31 days. After 31 days, contact the manufacturer for guidance.
  • You may return vaccine one time to ultra-cold temperature storage (-80°C to -60°C [-112°F to -76°F]).

See Pfizer-BioNTech COVID-19 Vaccine Storage and Handling Summary for more storage and handling information.

Vials can be at room temperature a total of 24 hours, provided the time limit before and after dilution is not exceeded:

  • Before dilution, vials can be stored between 8°C and 25°C (46°C and 77°C), including thawing time, for a maximum of 12 hours.
  • After dilution, vials can be stored between 2°C and 25°C (36°C and 77°C). Vials should be discarded 12 hours after dilution.

See the Fact Sheet for Healthcare Providers Administering Vaccine for this formulation.

12 years of age and older formulation (gray cap):

Vials can be at room temperature a total of 24 hours, provided the time limit before and after puncture is not exceeded. Do NOT dilute prior to use:

  • Vials can be stored between 8°C to 25°C (46°F to 77°F) for a total of 12 hours, including thawing time, prior to the first puncture.
  • After first puncture, the vial should be held between 2°C to 25°C (35°F to 77°F). Vials should be discarded 12 hours after first puncture.

After dilution, vials must be stored between 2°C and 25°C and used within:

  • 6 hours of dilution for vials of 12 years of age and older formulation (purple cap)
  • 12 hours of dilution for vials of 5 through 11 years of age formulation (orange cap)

After first puncture for vials of 12 years of age and older formulation (gray cap), vials must be stored between 2°C and 25°C and used within 12 hours.

Discard any remaining vaccine after this time according to your state immunization program’s directions for proper disposal.

For information about transporting vaccine in a syringe go to General FAQs. Additional guidance can be found at Pfizer-BioNTech COVID-19 Vaccine Transporting Vaccine for Vaccination Clinics Held at Satellite, Temporary, or Off-Site Locations.

Vaccine Administration

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 as well as 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. A person weighing more will require more of a medication to achieve the same effects that than a person weighing less would require.

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 (antigen-presenting cells) are directed to the injection site to attack foreign cells and produce antibodies and memory cells that will protect against future infection. The immune response generates memory cells and antibodies that travel throughout the body and will recognize the virus in the future.

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.

Learn more about:

Understanding How Vaccines Work

CDC recommends that children receive the vaccine dosage and formulation based on their age on the day of vaccination for each dose. If a child turns 12 years old between their first and second dose, administer a:

  • 2mL dose of the 5 through 11 years of age and older formulation (orange cap) for the first dose (when they are 11 years old)
  • 3mL dose of the 12 years of age and older formulation (purple cap or gray cap) for the second dose 21 days after the first dose (when they are 12 years old)

However, the FDA authorization allows children who will turn from 11 years to 12 years of age between their first and second dose in the primary series to receive the authorized dosage of either formulation for either dose. If such dosing occurs, the child is considered fully vaccinated. This is not considered an error and should not be reported to VAERS.

No. Preferences for a higher dosage or the same formulation are not reasons to delay vaccination. This leaves a child unprotected from COVID-19 longer than necessary. Clinical trials evaluate various dosing regimens to determine the best dosage and schedule that is both safe and effective in each age group. CDC recommends that children receive the vaccine dosage and formulation based on their age on the day of vaccination for each dose, even if this means they might receive a lower dosage or different formulation for each primary series dose.

Vaccine recipients should receive the correct vaccine formulation for their age. If the orange cap formulation is administered to a person

  • Aged 12 through 17 years old: Do NOT repeat the dose. If the dose given in error is the first dose, administer an age-appropriate dose 21 days after the dose given in error to complete the primary series.
    • As an exception, providers may use clinical judgement about the individual situation and repeat a dose of the age-appropriate formulation (12 years of age and older formulation; purple cap or gray cap) at an interval of 21 days after the dose given in error. For example, a provider may choose to repeat one dose with the age-appropriate formulation if an adolescent 12 years old or older receives two primary series doses of the orange cap formulation.
  • Aged 18 years and older: Repeat dose immediately. If the dose given in error is the first dose, administer another age-appropriate dose 21 days after the repeat dose to complete the primary series.

This is considered a vaccine administration error if the recipient is 13 years old or older. Providers are required to report COVID-19 vaccine administration errors to VAERS. For more information, see Appendix A.

No, you cannot use the 12 years of age and older formulation (purple cap or gray cap) to vaccinate a child between 5 through 11 years of age, even if it is one third of the purple cap dose. Although it might appear that one third of the purple or gray cap formulation (0.1 mL) would be equivalent to a 10ug concentration of mRNA per dose, the correct concentration of mRNA cannot be guaranteed in such a small volume of vaccine.

Pfizer recommends the use of a syringe with appropriate graduations to dilute with the directed 1.3 mL of saline for the 5 through11 years of age formulation. The impact to the final dose with a 1.2 mL or 1.4 mL dilution volume would be within 4% of the target dose. This suggests that using a syringe with 0.2 mL graduations and estimating the 1.3 mL volume will not significantly impact the intended dose.

Some ancillary supplies kits contain 100-unit (1 mL) insulin syringes to administer COVID-19 vaccine. Only 100-unit (U-100) insulin syringes will be included in the kits. If you have received insulin syringes in COVID-19 ancillary supplies, ensure staff is knowledgeable regarding how they should be used, including measuring the correct dosage (volume) of vaccine. Best practice considerations include:

  • One unit of U-100 insulin measures 0.01 mL in a U-100 units/1 mL syringe, therefore, 10 units of a U-100 insulin measures 0.1 mL in a U-100 units/1 mL syringe.
    • 5 through 11 years of age formulation (orange cap): 0.2 mL dosage = 20 units
    • 12 years of age and older formulation (purple cap): 0.3 mL dosage = 30 units
    • 12 years of age and older formulation (gray cap): 0.3 mL dosage = 30 units
  • Attach the correct needle length and gauge based on the vaccine recipient. The needle length is determined by the administration route, injection site, and recipient’s age. Gender and weight are additional considerations for people 19 years of age and older.

CDC recommends healthcare providers follow the dosing guidance from the manufacturer as outlined in the Fact Sheet for Healthcare Providers Administering Vaccine. CDC will update its guidance if the EUA or approval and ancillary supply kits support obtaining additional doses per vial in the future.

Contact the manufacturer. mRNA vaccine is very fragile and should not be shaken. Vials should only be gently inverted.

Some interim recommendations for COVID-19 vaccine administration errors differ from ACIP’s General Best Practice Guidelines. Review vaccine administration errors and deviations for COVID-19 vaccines to learn about the interim recommendation for each type of error.

For all vaccine administration errors:

Vaccine Safety and Efficacy

For adults, adolescents, and children, both doses are necessary for developing the most protection. Effectiveness of a single dose has been studied in phase III trials and some observational studies. Different studies have demonstrated different rates of effectiveness, but all have been lower than the effectiveness after 2 doses. Additionally, the duration of protection from a single dose is unknown.

Learn more about vaccine effectiveness of a single dose.

Vaccination of Minors

The federal government does not have specific requirements for medical consent for vaccination. States/jurisdictions have medical consent laws that address the circumstances under which a medical provider must seek consent prior to a medical procedure and the processes for obtaining that consent. These laws vary across jurisdictions. Providers may also be subject to policy requirements for consent within their own organizations.

To access COVID-19 vaccine in the United States, a provider must enroll in the Centers for Disease Control and Prevention (CDC) COVID-19 Vaccination Program and sign the applicable CDC Provider Agreement. The CDC COVID-19 Vaccination Program Provider Agreement requires the provider to comply with applicable patient assent and consent laws in their state/jurisdiction for administration of COVID-19 vaccines.

Some state, tribal, and territorial laws may require a parent or legal guardian to accompany an eligible minor to receive vaccinations. Some jurisdictions’ laws may allow parent/guardian consent without a requirement to be physically present for the vaccination if the provider is given evidence of the consent prior to vaccination. Providers may also have to comply with policy requirements determined by their organizations.

No, in-person provision of the Fact Sheet is not a federal requirement. Under the CDC COVID-19 Vaccination Program Provider Agreement, the vaccine provider may provide the Fact Sheet to the parent or legal guardian prior to the visit on paper, or through an electronic link if the individual agrees to receive it electronically.

There is no such federal requirement. If a state, tribal, or territorial patient consent law requires a parent or legal guardian to complete the prescreening questions for the minor, the CDC COVID-19 Vaccination Program Provider Agreement requires the provider to comply with such a requirement. In addition, if a jurisdiction authorizes a minor to consent to receipt of COVID-19 vaccine, the minor can complete the prescreening questions themselves, but the provider must confirm that this complies with state, tribal, or territorial laws.

A parent or legal guardian may complete the prescreening questions online provided this is done prior to administration of COVID-19 vaccine to the minor. Providers must comply with any applicable state, tribal, or territorial laws.

No. Since applicable medical consent laws are a matter of state, tribal, or territorial law, providers are advised to consult with legal counsel to assure compliance with the scope of those consent laws.

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Page last reviewed: March 23, 2022