At the same time, regulators have been concerned about data from Nordic countries and elsewhere that indicate that young male Moderna recipients may face an increased risk of myocarditis or inflammation of the heart muscle – a side effect that has also been linked to the Pfizer vaccine. Researchers have said that the absolute risk is still very small, most cases are mild and resolve quickly and that Covid-19 can also trigger myocarditis.
Concerns about myocarditis are behind the FDA’s decision to wait to approve the vaccine for adolescents.
The FDA said Friday that in reviewing broader booster eligibility for Modernas and Pfizer vaccines, it had examined recent virus cases and actual data on the risk of myocarditis and concluded that the benefits of a booster shot outweigh the risks. The FDA also noted that both companies conducted further studies on myocarditis risk.
At the heart of the booster debate is the question of what vaccines should do. Critics of the administration’s policy argue that despite a degree of diminishing protection, vaccines continue to fulfill their mission of protecting against serious illness and hospitalization.
Booster advocates such as Dr. Fauci oppose that the vaccines should also protect against symptomatic disease, especially since some patients avoid hospitalization but have long-term consequences.
“I do not know of any other vaccine that we only care about keeping people out of hospitals,” Dr. Fauci said at a White House briefing Wednesday. “I think one important thing is to prevent people from getting symptomatic disease,” including younger people.
In recent weeks, state after state has moved to allow booster shots for all adults, including Massachusetts, Rhode Island, Kansas, Kentucky, Maine, Vermont, Arkansas, California, Colorado and New Mexico.
A number of other countries have taken the same approach, including Australia, Brazil, Canada, Germany, Hungary, Israel, Japan, Norway and Saudi Arabia. EU regulators have approved booster doses of both Moderna and Pfizer-BioNTech for all adults.
Kitty Bennett contributed research.