Second mRNA COVID-19 Vaccine in Primary Series Can Be Extended to 8 Weeks for Some Individuals

The CDC updated their guidance for Pfizer-BioNTech (Comirnaty) and Moderna (Spikevax) mRNA COVID-19 vaccines on February 22 to include considerations for an 8 week interval between the first and second doses of the primary series for certain individuals. This guidance discusses that individuals 12 years and older can receive the second dose of the Pfizer-BioNTech vaccine 3-8 weeks after the first. Additionally, the interval for those 18 years and older for Moderna is 4-8 weeks.

This new update stems from data presented this month at the CDC’s Advisory Committee on Immunization Practices (ACIP) meeting about myocarditis and COVID-19 vaccine intervals. Evidence demonstrates that the risk of myocarditis with mRNA vaccines is low. However, the risk is higher in males 12-39 years of age after the second vaccine dose and is seen more with the Moderna vaccine. Myocarditis is inflammation of the heart muscle, and symptoms can include chest pain, shortness of breath, or heart palpitations.

Some studies in teens 12-17 years of age and adults demonstrated that extending intervals longer than 4 weeks may reduce the small risk of myocarditis associated with mRNA vaccines, produce higher antibody responses, and increase vaccine efficacy. However, extending the interval between doses beyond 8 weeks has not been shown to provide any additional benefits.

According to the CDC’s COVID-19 Vaccination data by age group, only 57% of individuals 12-17 years of age in the U.S. have completed their two dose COVID-19 vaccine series. One of the considerations of the ACIP for their updated guidance on extended intervals was to encourage vaccine hesitant parents concerned about myocarditis.

The CDC recommends COVID-19 vaccines to prevent complications such as myocarditis. One study demonstrated that COVID-19 patients have a 16 times higher risk of myocarditis than individuals without COVID-19. One recent study revealed that unvaccinated patients (12-30 years of age) with COVID-19 have a 17 times higher risk of developing myocarditis than COVID-19 vaccinated individuals.

Currently, there is no available data regarding extended COVID-19 vaccine intervals for children 5-11 years of age. Therefore, the recommended interval between the first and second dose of Pfizer-BioNTech for this population should remain at 3 weeks. 

The shorter 3-week interval for Pfizer-BioNTech and 4 weeks for Moderna between the first and second vaccine dose is still also recommended for the following groups: individuals who are moderately or severely immunocompromised; adults 65 years and older; and those who need protection quickly due to high community transmission or risk of developing severe COVID-19.