An investigational COVID-19 vaccine made by Novavax was found to be 90% effective at preventing COVID-19 illness, according to results from a Phase 3 clinical trial published today in the New England Journal of Medicine. In the study, researchers recruited nearly 30,000 adult volunteers at 113 clinical sites in the United States and six sites in Mexico. Approximately 20,000 participants received two doses of the vaccine spaced three weeks apart, and 10,000 received placebo. In addition to being highly effective in preventing COVID illness of any severity, the vaccine was 100% effective in preventing moderate and severe disease that required hospitalization. During the first few months of 2021 when the study was conducted, the predominant circulating strain was Alpha. The assessment did not include Delta or Omicron, the newest variant of concern, which had not begun to circulate. Most side effects were mild to moderate and transient. Fever was very rare. The most common side effects in the vaccine recipients included pain and tenderness at the injection site, headache, muscle aches, and fatigue that lasted a day on average. None of the recipients developed serious reactions such as heart inflammation or blood clots. “Our study results indicate that this vaccine is highly efficacious and very safe. In addition, this vaccine has many attractive features. It is made from a small piece of protein, like many currently licensed vaccines in the U.S. and has convenient refrigerator storage requirements, so it will be an important addition to the COVID-19 vaccine portfolio, in the U.S. and in countries where supply is lacking,” said Dr. Karen Kotloff, professor of pediatrics at University of Maryland School of Medicine’s Center for Vaccine Development and Global Health. The Novavax trial was part of Operation Warp Speed, a multi-agency collaboration led by the U.S. Department of Health and Human Services (HHS), which aims to accelerate the development, manufacturing, and distribution of medical countermeasures for COVID-19. Novavax, based in Gaithersburg, MD.