Moderna COVID-19 Vaccine Questions

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

Vaccination Schedule and Use

Yes. Second doses or additional primary doses of Moderna 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 24 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 23 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 (VAERSexternal icon).

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 at least 28 days between doses. Anyone for whom Janssen COVID-19 Vaccine is considered 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 Immunizationpdf icon. 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.

The dosage for the Moderna COVID-19 booster dose is 0.25 mL (50 microgram), which is half the volume of the 0.5 mL (100 microgram) dosage for the 2-dose primary series.

The 0.5 mL (100 microgram) dose should be used for a Moderna primary series and additional primary dose to ensure that the initial immune response to primary vaccination is sufficient. Do not use the 0.25 mL dose for the 2-dose primary series or additional primary dose.

The lower booster dose of 0.25 mL is recommended based on clinical trial data. Trial data demonstrated the lower booster dose was safe and effective.

  • Rates of adverse reactions with this dose were comparable to those observed after the second dose of the primary series.
  • Consistently high antibody titers were demonstrated, with a rise from pre-booster titer levels for both the original and Delta variants.

Learn more about the evidence for Moderna boosterspdf icon.

People 18 years of age and older who have completed a primary COVID-19 vaccine series with any age-appropriate FDA-approved or FDA-authorized product have the option to receive any of the FDA-approved or FDA-authorized COVID-19 booster products (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.

People 12 – 17 years of age who have completed a primary COVID-19 vaccine series with an age-appropriate Pfizer-BioNTech COVID-19 Vaccine should receive an age-appropriate Pfizer-BioNTech COVID-19 Vaccine for their booster dose.

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

People 18 years of age or older who received a mixed 2-dose mRNA primary vaccine series have the option to receive any of the FDA-approved or FDA-authorized COVID-19 booster products (Pfizer-BioNTech, Moderna [0.25 mL dose] or Janssen); however, an mRNA COVID-19 vaccine is preferred over the Janssen COVID-19 Vaccine.

Learn more about considerations for selecting which booster dose to receive.

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 (Pfizer-BioNTech recipients) or 18 years of age and older (Moderna recipients) 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 who received a 2-dose mRNA COVID-19 vaccine primary series should receive a booster dose at least 3 months after completing their additional primary dose. For people 12-17 years of age, only the age-appropriate Pfizer-BioNTech COVID-19 Vaccine can be used for booster vaccination. For people 18 years of age or older, the booster dose can be any FDA-approved or FDA-authorized COVID-19 vaccine; however, an mRNA COVID-19 vaccine is preferred over the Janssen COVID-19 Vaccine.

A patient can be vaccinated once symptoms resolve and if they have met the criteria to discontinue isolation. We do not have guidance for specific optimal time-period between infection and vaccination.

If the patient received 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.

Vaccine Indications, Contraindications, and Precautions

Moderna 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/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

Before puncturing the vial stopper, vaccine may be stored in the refrigerator between 2°C and 8°C (36°F and 46°F) for up to 30 days. After 30 days, contact the manufacturer for guidance before discarding any vials.

After the first dose has been withdrawn, the vial should be held between 2°C and 25°C (36°F and 77°F). Discard after 12 hours. Do not refreeze.

See Moderna COVID-19 Vaccine beyond-use date guidance and labelspdf icon.

No. After the first dose has been withdrawn, vials must be stored between 2°C and 25°C (46°F and 77°F) and used within 12 hours.

For information about transporting vaccine in a syringe go to General FAQs.

For specific information about transporting Moderna vaccine go to “Moderna Transporting Vaccine to Off-Site Clinicspdf icon

Unpunctured vials can be transported for up to 12 hours. This time is cumulative, including the amount of transport time to and from clinics. All transport time is also included in the 30-day time frame. For example, if your transport time to and from a clinic is a total of 2 hours, any unpunctured vials have 10 hours of transport time left. If there is a clinic the following day, you may transport the vaccine again for up to 10 hours. Use Moderna COVID-19 Vaccine beyond-use date/time (BUD) tracking labelspdf icon to track and record transport time. This only applies to unpunctured vials. Punctured vials must be discarded if not used within 12 hours.

Vaccine Administration

No. Moderna COVID-19 Vaccine comes in a multidose vial and does not require reconstitution.

See Moderna COVID-19 Vaccine Preparation and Administration Summarypdf icon for more information.

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.
    • Primary series dose (including additional primary dose): 0.5 mL dosage = 50 units
    • Booster dose: 0.25 mL dosage = 25 units
  • Attach the correct needle length and gaugepdf icon 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 Vaccineexternal icon. CDC will update its guidance if the EUA and ancillary supply kits support obtaining additional doses per vial in the future.

Do not puncture a vial of Moderna COVID-19 Vaccine more than 20 times. If punctured more than 20 times, the vial stopper will disintegrate. Bacteria may enter a compromised stopper and potentially cause bacterial infection in patients.

Discard the vial after 20 punctures, even if there is vaccine left in the vial. If administering only booster doses, there will be vaccine left in the vial.

Contact the manufacturer. mRNA vaccine is very fragile and should not be shaken. Vials should only be gently swirled while held upright.

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

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.

Page last reviewed: March 23, 2022