COVID-19 Vaccine: CDC Updates Guidance on Interchangeability, Dosage Intervals


The CDC’s Advisory Committee on Immunization Practices issued updates to its interim recommendations for mRNA COVID-19 vaccines.

covid vaccination

The CDC’s Advisory Committee on Immunization Practices (ACIP) has updated its interim recommendations for coronavirus disease 2019 (COVID-19) vaccines.

Recent changes include updates to guidelines on dose intervals, interchangeability, language on vaccination of individuals with a history of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and new recommendations for those with a history of dermal fillers.

These considerations only apply to the 2 currently authorized messenger RNA (mRNA) vaccines in the United States: Pfizer-BioNTech and Moderna COVID-19 vaccines. 

According to ACIP, under the emergency use authorization (EUA), the following age groups are authorized to receive vaccination:

  • Pfizer-BioNTech: aged 16 and older
  • Moderna: aged 18 and older

Dosage Intervals

Both vaccines consist of 2 doses administered intramuscularly. The Pfizer-BioNTech series is administered 3 weeks (21 days) apart and the Moderna series is administered 1 month (28 days) apart.

ACIP continues to recommend that the second dose of the vaccine series be given as close as possible to the recommended interval.

What’s new: If it is not feasible to adhere to the recommended timeframe, ACIP said the second dose may be scheduled for administration up to 6 weeks, or 42 days, after the first dose. There are limited data to show that mRNA COVID-19 vaccine doses administered beyond that interval remain effective; however, ACIP indicated that patients who receive their second dose more than 6 weeks after their first dose do not have to start over.


Although either of the currently authorized vaccines can be used when indicated, ACIP states that the vaccines are not interchangeable with each other or with other COVID-19 vaccine products. As such, ACIP recommends that both doses of the series be completed with the same product.

ACIP offers strategies to help immunizers ensure patients receive their second dose with the appropriate product and interval between doses:

  1. Provide COVID-19 vaccination record cards to vaccine recipients, ask recipients to bring their card to their appointment for the second dose, and encourage recipients to make a backup copy.
  2. Encourage vaccine recipients to enroll in VaxText, a free text message-based platform to receive COVID-19 vaccination second dose reminders.
  3. Record each recipient’s vaccination in the immunization information system.
  4. Record vaccine administration in the patient’s medical record.
  5. Make an appointment for the second dose before the vaccine recipient leaves.

What’s new: In rare cases, where the first-dose vaccine product cannot be determined or is no longer available, ACIP acknowledged that any available mRNA COVID-19 vaccine may be administered at a minimum interval of 28 days between doses. 

Contraindications and Precautions

Additionally, ACIP cautions that individuals with a history of an immediate allergic reaction (of any severity) to an mRNA-COVID-19 vaccine might be at greater risk for anaphylaxis upon re-exposure.

CDC considers a history of the following to be a contraindication to vaccination with both the Pfizer-BioNTech and Moderna COVID-19 vaccines:

  1. Severe allergic reactions (e.g. anaphylaxis) after a previous dose of an mRNA COVID-19 vaccine or any of its components
  2. Immediate allergic reactions of any severity to a previous dose of an mRNA COVID-19 vaccine or any of its components (including polyethylene glycol [PEG])
  3. Immediate allergic reaction of any severity to polysorbate (due to potential cross-reactive hypersensitivity with the vaccine ingredient PEG)

Those with a history of an immediate allergic reaction of any severity to polysorbate should not receive mRNA COVID-19 vaccination at this time unless they’ve been evaluated by an allergist-immunologist and it is determined that the individual can safely receive the vaccine.

What’s new: According to the guidance, patients with injectable dermal fillers may experience swelling at the filler injection site following receipt of a vaccine dose. This swelling has shown to be temporary and resolved with treatments. As long as they have no other contraindication, ACIP recommends they receive the vaccination.

ACIP also updated language on vaccination for individuals who have had SARS-CoV-2 infection.

Visit the CDC’s website to read the full guidance.


  1. CDC. mRNA COVID-19 Vaccines. Last updated January 21, 2020. Accessed January 26, 2020.
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