The Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) has issued an update to their interim recommendations regarding the use of mRNA vaccines authorized for the prevention of coronavirus disease 2019 (COVID-19).

Two mRNA COVID-19 vaccines have been authorized for emergency use by the Food and Drug Administration. The Pfizer-BioNTech vaccine is administered as a 2-dose series 21 days apart, while the Moderna vaccine is given as a 2-dose series 28 days apart.

The ACIP continues to recommend that the second dose of vaccine be given as close as possible to the recommended interval; however, if this is not feasible, the second dose may be scheduled for administration up to 42 days (6 weeks) after the first dose.

Individuals who have received their first dose of vaccine should receive the second dose with the same product. The authorized COVID-19 vaccines are not interchangeable with each other and the safety and efficacy of using mixed products in a series have not been evaluated.

A summary of additional changes made to the guidance can be found here.


Interim clinical considerations for use of mRNA COVID-19 vaccines currently authorized in the United States. US Centers for Disease Control and Prevention website. Accessed January 21, 2020.