First COVID-19 vaccine tested in U.S. shows promising results

No volunteers experienced a serious side effect, but more than half reported mild or moderate reactions.

Biotech firm Moderna Inc's experimental vaccine for COVID-19 showed it was safe and provoked immune responses in all 45 healthy volunteers in an ongoing early-stage study, U.S. researchers reported on Tuesday.

Volunteers who got two doses of the vaccine had high levels of virus-killing antibodies that exceeded the average levels seen in people who had recovered from COVID-19, the team reported in the New England Journal of Medicine.

No study volunteers experienced a serious side effect, but more than half reported mild or moderate reactions such as fatigue, headache, chills, muscle aches or pain at the injection site. These were more likely to occur after the second dose and in people who got the highest dose.

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