Vaccine side effects rare and outweighed by benefits, CDC reported

For adults, the benefits of the three coronavirus vaccines authorized in the United States outweigh the risks of serious side effects, which remain rare, according to a new report from the Centers for Disease Control and Prevention.

The Pfizer-BioNTech and Moderna vaccines have been linked to inflammation of the heart muscle, known as myocarditis, and the Johnson & Johnson vaccine may increase the risk of a rare blood-clotting disorder and a neurological condition known as Guillain-Barré syndrome. All of the conditions can be serious but remain uncommon.

These small risks are exceeded by the benefits of the vaccines, which provide powerful protection against disease and death, experts concluded. For instance, every 1 million doses of the Johnson & Johnson vaccine that are administered are likely to prevent roughly 1,800 hospitalizations and 140 deaths, while causing 14 to 17 cases of Guillain-Barré and 1 to 2 cases of the blood-clotting disorder, according to the paper, which was published Tuesday.

The paper is based on data reported to the federal Vaccine Adverse Events Reporting System. The database contains unverified reports, but researchers confirmed many of the cases used in their calculations, which were initially presented at a July meeting of the CDC’s vaccine advisory group.

As of June 30, roughly 12.6 million doses of the Johnson & Johnson vaccine had been given to U.S. adults. As of that date, there had been 100 reports of Guillain-Barré, which can cause muscle weakness and paralysis, a rate of 7.8 cases per 1 million doses. The risk was highest for men between 50 and 64, who developed the side effect at a rate of 15.6 per 1 million doses.

By the end of June, there had also been 497 reports of myocarditis after the second dose of either the Pfizer or the Moderna vaccines, a rate of 3.5 cases per 1 million doses. That increased to 24.3 cases per 1 million for men between 18 and 29, among whom myocarditis was most common.

The CDC and the Food and Drug Administration will continue to monitor reports of adverse events, the report noted.

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