New research suggests that the protection provided by the Modern COVID-19 vaccine lasts 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 tests on 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 appeared and began to spread.
A separate report in the medical journal raises concerns about variants. The scientists measured antibodies that can block the virus in 50 people who had received Sinopharm or Sinovac vaccines developed in China. Many showed a total or partial loss of efficacy against a virus variant first detected in South Africa.
Vaccines still seemed to protect against a variant that was first found in the UK and is rapidly spreading to the United States and elsewhere.
Pfizer and Moderna have said they are working to upgrade their vaccines or possibly design a booster shot, should variants be needed.