Moderna COVID-19 vaccine induced adverse reactions in 'more than half' of trial participants

One-fifth of participants in one test group reported 'one or more severe adverse events.'

Updated: July 15, 2020 - 12:24pm

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A highly anticipated clinical trial for a potential COVID-19 vaccine managed in part by the American drug company Moderna has resulted is some adverse effects in more than half of the trial's participants, with one test group reporting "severe" symptoms. 

The trial, which is also being sponsored by the National Institute of Allergy and Infectious Diseases, administered the vaccine "as a 0.5-ml injection in the deltoid muscle" in two shots spaced about one month apart. Two separate groups received 25-microgram and 100-microgram doses, respectively. A third group with a 250-microgram dose was subsequently added. 

The vaccine "induced anti–SARS-CoV-2 immune responses in all participants," the research team reported Tuesday in the New England Journal of Medicine. Researchers said that "no trial-limiting safety concerns were identified." Yet a majority of participants still reported at least one side effect. 

"Solicited adverse events that occurred in more than half the participants included fatigue, chills, headache, myalgia, and pain at the injection site," the report states. Fever, joint pain and nausea were also reported. 

Side effects grew more common with more (and larger) injections, the scientists write: "Systemic adverse events were more common after the second vaccination, particularly with the highest dose, and three participants (21%) in the 250-μg dose group reported one or more severe adverse events."

Notably, every participant in the two larger-dose groups reported adverse reactions after their second injections. One study participant in the smallest-dose group, meanwhile, was removed due to having developed hives after the first round of injections. 

The scientists said that due to the ongoing status of the project, they are not yet "able to assess the durability of the immune responses" generated by the vaccine, but that they intend to follow participants "for 1 year after the second vaccination" and examine regular blood samples to monitor the vaccine's effects. 

A large trial "expected to evaluate a 100-μg dose" is "anticipated to begin during the summer of 2020," the report states.

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