Health and Science

CDC says waiting longer between Pfizer, Moderna doses may reduce rare myocarditis risk for younger men

Key Points
  • The CDC said males ages 12- to 39-years-old should consider waiting eight weeks between the first and second doses of Pfizer's and Moderna's vaccines.
  • Public health authorities in Canada found that the risk of myocarditis is lower for younger men when they wait eight weeks.
  • The risk of myocarditis is low after vaccination. U.S. health authorities have said Covid infection poses a higher risk of heart inflammation.

In this article

A healthcare worker prepares a dose of the Pfizer-BioNTech Covid-19 vaccine at a vaccination clinic in the Peabody Institute Library in Peabody, Massachusetts, on Wednesday, Jan. 26, 2022.
Vanessa Leroy | Bloomberg | Getty Images

The U.S. Centers for Disease Control and Prevention said this week that younger males should consider waiting longer between doses of Pfizer's and Moderna's vaccines to reduce a rare risk of heart inflammation.

The CDC said males ages 12- to 39-years-old should consider waiting eight weeks between the first and second doses of their primary Covid vaccination series. Public health authorities in Canada found the risk of myocarditis in men ages 18- to 24-years-old was lower when they waited eight weeks for the second dose of Moderna or Pfizer.

The CDC recommends that other eligible individuals wait three weeks between Pfizer shots and four weeks between Moderna doses, particularly the elderly and those with compromised immune systems.

Myocarditis is an inflammation of the heart muscle than can result in serious health problems, according to the National Heart, Lung and Blood Institute. Myocarditis most commonly occurs after viral infections, but the CDC has also found a link with between Moderna's and Pfizer's shots and myocarditis, particularly after the second dose.

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The risk of myocarditis among men ages 18 to 39 is about 1.5 times higher after a second Moderna dose than with Pfizer's vaccine. Men in this age group report about 68 myocarditis cases per 1 million Moderna second doses administered, compared with 47 myocarditis cases per 1 million Pfizer second doses administered.

Most patients who develop myocarditis after Covid vaccination respond well to medicine and recover fully, according the CDC. People face a much higher risk of developing myocarditis after Covid infection than from the vaccines, according to the Department of Health and Human Services.