But with the variant circulating in South Africa, there was a sixfold reduction in the antibodies’ effectiveness. Even so, the company said, those antibodies “remain above levels that are expected to be protective.”
The results have not been published or peer-reviewed yet, but have been submitted to BioRxiv, which posts preliminary studies online. Moderna collaborated on the study with the Vaccine Research Center at the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.
Dr. Zaks said that the new version of the Moderna vaccine, aimed at the South African variant, could be used if needed as a booster one year after people received the original vaccine.
The need for such a booster may be determined by blood tests to measure antibody levels or by watching the population of vaccinated people to see if they begin falling ill from the new variant.
“We don’t yet have data on the Brazilian variant,” Dr. Zaks said. “Our expectation is that if anything it should be close to the South African one. That’s the one with the most overlap.” New forms of the virus will continue to emerge, he said, “and we’ll continue to evaluate them.”
Noting that Moderna took 42 days to produce the original vaccine, he said the company could make a new one “hopefully a little faster this time, but not much.”
One reason the current vaccine remains effective is a “cushion effect,” meaning it provokes such a powerful immune response that it will remain highly protective even with some drop in antibody strength, Dr. Anthony S. Fauci, the government’s leading expert on infectious diseases, and President Biden’s adviser on the coronavirus, said at a news briefing on Friday.