New research suggests that the protection provided by the Modern COVID-19 vaccine lasts for at least six months.
The report published Tuesday in the New England Journal of Medicine echoes what Pfizer said last week about its vaccine, which works in a similar way.
Both reports were based on follow-up testing of dozens of people who received the injections during the studies that led to the use of the vaccines. Those studies were conducted before worrisome new variants, or versions of the coronavirus emerged and began to spread.
A separate report in the medical journal raises concern about the variants. The scientists measured the antibodies that can block the virus in 50 people who had received the Sinopharm or Sinovac vaccines that were developed in China. Many showed a total or partial loss of efficacy against a variant of the virus first detected in South Africa.
The vaccines still appeared to protect against a variant that was first found in the UK and is now spreading rapidly in the US and elsewhere.
Pfizer and Moderna have said they are working to update their vaccines, or possibly design a booster vaccine, in case they are needed against variants.