Moderna Inc's experimental vaccine was 94.5% effective in preventing COVID-19 based on interim data from a late-stage trial, the company said on Monday.
That followed last week's news that Pfizer Inc's vaccine was also more than 90% effective based on initial data.
Pending more safety data and regulatory review, the United States could have two vaccines authorized for emergency use in December. Both vaccines employ synthetic messenger RNA (mRNA), which coaxes cells to make certain virus proteins that the immune system sees as a threat and mounts a response against.
Moderna's trial involved 30,000 racially diverse U.S. adults, including people at high risk for severe COVID-19. Only five of the 95 COVID-19 cases in the initial analysis occurred in participants who received the vaccine, while the rest had received a placebo.
The vaccine, administered in two shots 28 days apart, also appeared to prevent cases of severe COVID-19. Side effects, largely occurring after the second shot, included muscle aches, fever, headache and redness at the injection site.
Moderna's vaccine does not need ultra-cold storage like Pfizer's, making it easier to distribute. Moderna expects it to be stable at normal refrigerator temperatures of 2 to 8 degrees Celsius (36 to 48°F) for 30 days and can be stored for up to 6 months at -20C.
Explainer: Why it takes time to create a vaccine