There have been numerous reports of mRNA COVID-19 vaccine recipients being asked to return earlier than the recommended interval to receive their second dose. Frequently, this has been caused by a misunderstanding about the intent of allowing a 4-day grace period when determining the interval between dose one and dose two.

When the clinical considerations for COVID-19 vaccines were first published by CDC, they included the concept that a “grace period” of 4 days was allowable if the minimum interval between doses was inadvertently shortened. A similar grace period has been in place for other vaccines for many years. However, the grace period was intended to be used only when a vaccine was determined retroactively to have been given at less than the recommended minimum interval. In that case, a dose given within 4 days of the recommended interval would not have to be repeated. The grace period was not intended to be used when scheduling future vaccination visits. 

For COVID-19 vaccines currently available in the U.S., the recommended interval that should be used for scheduling between dose one and dose two is:

  • Pfizer-BioNTech — 21 days
  • Moderna — 28 days

On Jan. 6, 2021, CDC revised its Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States to emphasize the necessity of vaccinating according to the recommended schedule. The information regarding dosing intervals is summarized below:

  • Routine Scheduling. Do not schedule people to receive dose two earlier than the recommended intervals (i.e., 21 days for Pfizer-BioNTech or 28 days for Moderna).
  • Inadvertent Early Doses. If dose two is inadvertently administered as much as 4 days too early (“grace period”), it may be considered valid, but this 4-day period should not be utilized for routine scheduling.
  • No Maximum Interval. There is no maximum interval between dose one and dose two for either vaccine. If dose two is administered beyond 21 (Pfizer-BioNTech) or 28 days (Moderna), there is no need to restart the series.

Visit CDC's Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States for full details.

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Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.