CDC increases recommended wait period between doses of COVID-19 mRNA primary series vaccines for some people

The Centers for Disease Control and Prevention (CDC) recommends that some people, especially males ages 12-39, wait up to eight weeks between the first and second doses of a Moderna or Pfizer primary vaccine series. While the risk is already low, recent studies suggest that a longer wait between doses may further reduce the risk of the heart condition, myocarditis, following vaccination. Studies have also shown that more antibodies get built when primary doses are spread at least six weeks apart, which may improve vaccine efficacy.

graphic explaining new guidance on how long to wait between doses of an mRNA primary series vaccine.

The CDC continues to recommend that people who are moderately to severely immunocompromised and those 65 and older receive a second dose of an mRNA vaccine (Moderna or Pfizer) as soon as they are eligible. “If you’re at high risk from COVID-19, don’t wait,” said Paul Cieslak, medical director for communicable diseases and immunizations at Oregon Health Authority. “Get your second dose as soon as you can: for Pfizer that’s 21 days after the first dose, and for Moderna, 28 days.”

Myocarditis is an inflammation of the heart muscle. Most people who experience this after vaccination recover quickly with minimal treatment. Myocarditis is most common in males ages 12-39 and occurs more often after the second dose of an mRNA vaccine. Being infected with COVID-19 also carries risk of myocarditis. A large study from March 2020-Jan. 2021 showed hospital patients with COVID-19 were nearly 16 times more likely to develop myocarditis than patients who did not have COVID-19.

Vaccination benefits outweigh the risk

“Young men occasionally get myocarditis after vaccination with Pfizer or Moderna,” Cieslak said. “But one study showed they were 100 times more likely to be hospitalized with COVID-19, if they weren’t vaccinated, than they were to get myocarditis from a vaccine.”

The CDC estimates a Moderna or Pfizer primary vaccine series given to 1 million males ages 18-39 will prevent nearly 2,000 COVID-19-related hospitalizations. There are fewer than 70 myocarditis cases per 1 million second doses given.

“Getting vaccinated is much safer than not getting vaccinated,” Cieslak said.