With several European nations rethinking their endorsements of giving the Moderna vaccine to young people, the FDA will study a potential side effect longer before deciding on approval. The issue is myocarditis, a rare inflammatory heart condition, the Wall Street Journal reports. Finland, Sweden, Denmark, and Norway have called for not administering the Moderna doses to anyone under 30. Norway recommends that men younger than 30 consider switching to Pfizer—the market leader—if they've had one Moderna shot, per the Journal.
In the US, Moderna is approved for anyone 18 or older, but the company wants that expanded to 12- to 17-year-olds. Regulators don't know whether a Moderna dose increases the chances of developing myocarditis. Moderna's shot was tested in more than 3,700 adolescents, the company reported, and was found to be effective, without any cases of myocarditis. FDA data shown to its vaccine advisory panel Thursday showed that myocarditis and pericarditis, another heart-related condition, showed up most often in men 18 to 25 who'd received a second dose of an mRNA vaccine. But the rates were no different for the Moderna and Pfizer vaccines.
A Canadian province, Ontario, last month recommended Pfizer for men 18-24, saying Moderna's vaccine brought a slightly higher risk, per the CBC. Officially, both vaccines can be given to patients 12 or older in European Union nations, though in practice, Moderna's use has been limited in some places. In the UK, for example, teenagers receive one shot of Pfizer's vaccine. When myocarditis cases do surface, they're usually mild, researchers say. In the worst cases, the condition can cause an abnormal heartbeat and death. A recent CDC study found that Moderna's vaccine did a better job of keeping COVID-19 patients from hospitalization than its Pfizer and Johnson & Johnson competitors. (Read more Moderna stories.)