New research suggests that the protection offered by the Moderna vaccine against COVID-19 lasts at least six months.
The report, published Tuesday in the New England Journal of Medicine, reflects what Pfizer said last week about the vaccine, which works in a similar way.
Both reports are based on follow-up tests in dozens of people who received the shots during studies that led to the use of the vaccines. These studies were done before new variants, or versions of the coronavirus, emerged and began to spread.
A separate report in the medical journal contributes to concerns about the variants. Scientists have measured antibodies that could block the virus in 50 people who received the vaccines Sinopharm or Sinovac developed in China. Many have shown complete or partial loss of efficacy against a virus variant first detected in South Africa.
The vaccines appear to be still protected against a variant first found in the UK and now rapidly spreading in the United States and elsewhere.
Pfizer and Moderna said they are updating their vaccines, or possibly designing a booster shot, if needed at variants.