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

Moderna COVID-19 Vaccine is authorized and recommended for people ages 18 years and older.

All people 18 years of age and older should receive a 2-dose primary series of the age-appropriate product spaced 28 days apart. Do not schedule vaccine recipients to receive the second dose earlier than the recommended interval. Additionally,

  • Moderately or severely immunocompromised people 18 years of age and older should receive an additional primary dose of Moderna vaccine at least 28 days after the 2-dose primary series.
  • People 18 years of age and older, including moderately or severely immunocompromised people, should receive a booster dose at least 6 months after the primary series (i.e., after the second dose or after the additional primary dose for immunocompromised persons). The booster dose can be Moderna, Pfizer-BioNTech, or Janssen.

Learn more about the COVID-19 vaccine schedule and who is recommended to receive an additional primary dose or booster dose.

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).

No. The grace period cannot be used to schedule second doses. Administer doses as close to the 28-day interval as possible, but not earlier than recommended. The grace period should be used only for retrospectively reviewing records. If it is discovered a dose has been inadvertently administered within a grace period of 4 days before the recommended date for the second dose (i.e., 24–27 days after the first dose), the dose is considered valid.

No. You should administer the second dose as close as possible to the recommended interval of 28 days after the first dose. However, if the second dose is administered after this interval, there is no need to restart the series.

All doses of the primary series and the additional primary dose should be completed with the same product. Make every effort to determine which vaccine product was administered as the first dose to ensure your patient completes the vaccine series with the same product. In exceptional situations, when the vaccine product given for the first dose cannot be determined or is no longer available, you may administer any available mRNA COVID-19 vaccine, with a minimum of 28 days between doses.

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. See contraindications and precautions for more information on use of Janssen COVID-19 Vaccine and additional precautions in people with a contraindication to mRNA COVID-19 vaccines.

No. When the same mRNA vaccine product is temporarily unavailable, it is preferable to delay the second dose to administer the same product rather than administer a mixed series using a different product.

Learn more about interchangeability of COVID-19 vaccine products.

Yes. You may administer a COVID-19 vaccine before, at the same visit, or after other vaccines without regard to timing (including live, attenuated vaccines). If a patient is due for more than one vaccine, providers are encouraged to offer all of the vaccines at the same visit. Coadministration of all recommended vaccines is important because it increases the probability that people will be fully vaccinated. It is also an important part of immunization practice if a healthcare provider is uncertain that a patient will return for additional doses of vaccine.

Learn more about coadministration with other vaccines.

Booster Doses

Everyone 18 years of age and older that received a 2-dose mRNA COVID-19 vaccine series should receive a single booster dose at least 6 months after completing the primary vaccine series.  The booster dose can be Moderna, Pfizer-BioNTech, or Janssen.

Learn more about considerations for COVID-19 vaccine booster doses.

The 6-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 October 1, 2021.

Yes. The 4-day grace period applies to the booster dose. A booster dose of Moderna COVID-19 Vaccine administered up to 4 days before the recommended date (4-day grace period) is considered valid. Use the grace period when retrospectively reviewing records to determine the validity of a dose. Do not use the grace period to schedule doses.

If a booster dose is administered earlier than the grace period (i.e., earlier than 4 days before the 6-month interval from the primary series), do not repeat the dose. 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 Systemexternal icon.

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 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 12 years of age and older formulation [purple cap]), Moderna [0.25 mL dose] or Janssen). Discuss the risks and benefits and which product may be most appropriate with individual patients.

Clinical trial data using homologous (the same) or heterologous (“mix and match”) boosters show that both increase immune response.

The frequency and type of local and systemic symptoms after a booster dose are generally similar to those experienced after a primary series. The rare risks of serious adverse events after a homologous or heterologous booster dose are also expected to be similar to those experienced after a primary series. These include:

  • Myocarditis and pericarditis: Based on data after receipt of an mRNA COVID-19 primary series, the group at the highest risk for myocarditis and pericarditis is males aged 12-29 years. Accumulating evidence from multiple sources suggests a higher risk for myocarditis following primary vaccination with Moderna compared to Pfizer-BioNTech. There are currently no data comparing the risk for myocarditis after a booster dose of Pfizer-BioNTech COVID-19 Vaccine versus a booster dose of Moderna COVID-19 Vaccine.
  • Guillain-Barre Syndrome: Based on data after receipt of a Janssen COVID-19 Vaccine primary dose, the group at the highest risk for GBS is men 50-64 years.
  • Thrombosis with thrombocytopenia syndrome (TTS): The group at highest risk for TTS is women ages 18–49 years. These women should be made aware of the increased risk for TTS and the availability of mRNA COVID-19 vaccines for a booster dose. People who developed TTS after their initial Janssen vaccines should not receive a Janssen booster dose.

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

People 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).

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

People 12 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 an mRNA COVID-19 vaccine primary series should receive an additional primary dose of the same mRNA vaccine received for the primary series 28 days after the completion of a primary series.

These people should receive a booster dose at least 6 months after completing their additional primary dose if they are 18 years of age or older.

The booster dose can be any FDA-approved or FDA-authorized COVID-19 vaccine, even if it is a different product than the primary series.

If a booster dose is given at any time earlier than the recommended interval (i.e., earlier than 6 months after completion of the mRNA primary series), do not repeat the dose.

Administering booster doses prior to the 4-day grace period 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 Systemexternal icon.

Yes. Eligible people that experience COVID-19 after being fully vaccinated can receive a booster dose. People with known current SARS-CoV-2 infection should defer vaccination at least until they have recovered from the acute illness (if they had symptoms) and have met criteria to discontinue isolation. Current evidence about the optimal timing between SARS-CoV-2 infection and vaccination is insufficient to inform guidance.

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.

Vaccine Indications, Contraindications, and Precautions

Most people can receive a COVID-19 vaccine; however, there are some situations in which CDC recommends deferring vaccination. See COVID-19 Vaccine FAQs for Healthcare Professionals: Vaccine Indications for more information.

Moderna COVID-19 Vaccine and Risk of Myocarditis/Pericarditis

Myocarditis is inflammation of the heart muscle, and pericarditis is inflammation of the outer lining of the heart. In both cases, the body’s immune system causes inflammation in response to an infection or some other trigger. Symptoms can include chest pain, shortness of breath, or palpitations.

The severity of cases of myocarditis and pericarditis can vary. For the cases reported after mRNA COVID-19 vaccination, most who presented to medical care have responded well to medications and rest.

The ACIP COVID-19 Vaccines Work Group reviewed:

  • Clinical trial and post-authorization safety data for myocarditis/pericarditis after receipt of mRNA COVID-19 vaccines
  • A risk-benefit assessment of myocarditis after receipt of mRNA COVID-19 vaccines

On June 23, 2021, after reviewing available evidence, ACIP determined that the benefits of using mRNA COVID-19 vaccines under the FDA’s Emergency Use Authorization (EUA) clearly outweigh the risks of myocarditis/pericarditis in all populations, including adolescents and young adults.

For more information see: Use of mRNA COVID-19 Vaccine After Reports of Myocarditis Among Vaccine Recipients: Update from the Advisory Committee on Immunization Practices — United States, June 2021

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 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. A person is considered fully vaccinated against COVID-19 2 or more weeks after receipt of the second dose in a 2-dose series (Pfizer-BioNTech and Moderna) or 2 or more weeks after receipt of the single dose of the Janssen vaccine. A person who only receives one dose of a 2-dose mRNA COVID-19 vaccine series is not considered fully vaccinated.

It is unclear if people who developed myocarditis or pericarditis after a first dose of an mRNA COVID-19 vaccine may be at increased risk of further adverse cardiac effects following a second dose of the vaccine. 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. Decisions about proceeding with the second 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

There are two options for storing Moderna COVID-19 Vaccine. It may be stored in:

  1. Freezer between -50°C and -15°C (-58°F and 5°F) up to the expiration or beyond-use date (BUD). Keep vaccine vials in their box, and place in the storage unit.
  2. Refrigerator between 2°C and 8°C (36°F and 46°F) for up to 30 days prior to its first use. Do not refreeze.

Refer to the Moderna COVID-19 Vaccine product information or Moderna COVID-19 Vaccine Storage and Handling Summarypdf icon for more detailed information on storage.

Yes. 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.

CDC requires vaccination providers participating in the COVID-19 Vaccination Program to use a specific type of TMD called a “digital data logger” (DDL) to monitor temperatures. A DDL provides the most accurate storage unit temperature information, including details on how long a unit has been operating outside the recommended temperature range (referred to as a “temperature excursion”). DDLs using a buffered temperature probe provide the most accurate way to measure actual vaccine temperatures. Always use DDLs with a current and valid Certificate of Calibration Testing.

For more storage and handling information, see:

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.

If the vaccine experienced problems during shipment (for example, damage or temperature excursion), contact

McKesson Specialty Customer Service at (833) 343-2703, Monday–Friday, 8 AM–8 PM Eastern Time.

If the vaccine experienced problems after it was received and placed into storage, contact the vaccine manufacturer for guidance on improper storage and handling. For temperature excursions affecting Moderna COVID-19 Vaccine, see Moderna’s temperature excursion toolexternal icon.

For temperature excursions (out-of-range temperatures), take immediate action:

  • Label the vaccine “Do Not Use” and store at the recommended temperature range until you receive manufacturer guidance.
  • Document the date and length of time of the excursion, storage unit temperature, room temperature, and inventory affected.
  • Record any other relevant information.
  • Contact the manufacturer for guidance on whether to use affected vaccines and whether patients need to be called for revaccination.
  • Document the event and action taken for record-keeping requirements.

CDC recommends transporting vaccine in vials. However, there may be instances when the only option is to transport predrawn vaccine in a syringe. U.S. Pharmacopeia includes guidance for transporting predrawn vaccine in syringes in the COVID-19 Vaccine Handling Guides: Operational Considerations for Healthcare Practitionersexternal 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:

Some people may have received a COVID-19 vaccine outside of the United States.

People who were vaccinated outside the United States with Pfizer-BioNTech, Moderna, or Janssen COVID-19 Vaccines:

  • Are considered fully vaccinated if they received all recommended doses of a single or 2-dose primary series.
  • Do not need to restart the series if they received the first dose of a 2-dose mRNA COVID-19 vaccine series. Administer a second dose as close to the recommended time as possible.
  • Should receive an additional primary dose if 12 years of age or older and moderately or severely immunocompromised, following the same guidance for people vaccinated in the United States
  • Should receive a booster dose if 18 years of age or older, following the same guidance for people vaccinated in the United States

People who completed all of the recommended doses of a World Health Organization Emergency Use Listing (WHO-EUL) COVID-19 vaccine that is not FDA-approved or FDA-authorized, and people who completed a heterologous (mix and match) series composed of any combination of FDA-approved, FDA-authorized, or WHO-EUL COVID-19 vaccines:

  • Are considered fully vaccinated.
  • Should receive an additional primary dose of Pfizer-BioNTech COVID-19 Vaccine at least 28 days after completion of the second dose of the primary series, if moderately or severely immunocompromised and at least 12 years of age.
  • Should receive a single booster dose of Pfizer-BioNTech COVID-19 Vaccine at least 6 months after completing the primary series (i.e., after the last dose of the initial primary series or after the additional primary dose for immunocompromised people), if 18 years of age or older.

People who received only the first dose of a multidose WHO-EUL COVID-19 primary series that is not FDA-approved or FDA-authorized, or who received all or some of the recommended doses of a COVID-19 vaccine primary series that is not listed for emergency use by WHO:

  • Should be offered primary vaccination with Pfizer-BioNTech, Moderna, or Janssen COVID-19 Vaccine, with a minimum interval of at least 28 days since receipt of the last dose of vaccine.
  • Are considered fully vaccinated after completion of primary vaccination and are not recommended to receive an additional primary dose or booster dose at this time.

Learn more about guidance for people who received COVID-19 vaccine outside the United States.

Vaccine Safety and Efficacy

Before vaccination, counsel patients about expected local and systemic side effects.

Common side effects include:

Local reactions:

  • Pain
  • Redness
  • Swelling

Systemic reactions:

  • Tiredness
  • Headache
  • Muscle pain
  • Chills
  • Fever
  • Nausea

Clinical trial data demonstrated vaccine efficacy was 94.1% against symptomatic, laboratory-confirmed COVID-19 following receipt of 2 doses of Moderna COVID-19 Vaccine.

Learn more about COVID-19 Vaccine Effectiveness.

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: December 6, 2021