The recently authorized COVID-19 vaccine developed by Moderna and the National Institute of Allergy and Infectious Diseases (NIAID) was 94.1% effective in preventing symptomatic COVID-19, according to phase 3 trial results published December 30 in The New England Journal of Medicine.

No cases of severe COVID-19 occurred among participants who received the vaccine, known as mRNA-1273, and there were no safety concerns.

The US Food and Drug Administration on December 18 issued an emergency use authorization for the vaccine, a lipid-nanoparticle-encapsulated mRNA vaccine expressing the prefusion-stabilized spike glycoprotein.

The trial began in July and enrolled 30,420 adults in the United States. Volunteers were randomly assigned in a 1:1 ratio to receive either two doses of the vaccine or two shots of saline placebo 28 days apart. The average age of the participants was 51 years.

In all, 196 cases of symptomatic COVID-19 occurred at least 14 days after participants received their second shot — 185 cases in the placebo group, and 11 in the vaccine group.

In a secondary analysis that included cases that occurred at least 14 days after the first shot, vaccine efficacy was 95.2%, study author Lindsey R. Baden, MD, of Brigham and Women’s Hospital, Boston, Massachusetts, and colleagues report.

About half of the participants who received mRNA-1273 experienced moderate to severe side effects, such as fatigue, muscle aches, joint pain, and headache, after the second dose. Most adverse events resolved within 20 days.

*Story in Medscape News

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