New Covid Booster Strengthens Immune Response Against Subvariants, Moderna Says

WASHINGTON — A new study by Moderna suggests that its updated coronavirus booster strengthens a key component of the immune system’s defense against the Omicron subvariant that currently accounts for nearly one in three infections in the United States.

The company announced the findings in a news release on Monday. The underlying data has not yet been published or peer-reviewed, but it has been reviewed by federal regulators. The data indicates that Moderna’s new booster generates significantly higher levels of neutralizing antibodies against BA.5. and its sister subvariant of Omicron, BA.4, than the previous booster. BA.5 accounts for about 30 percent of infections in the United States.

In the study, 511 participants received the updated booster and about 300 received the previous booster, Moderna officials said. That makes the study the largest to date of the updated boosters, which the federal government introduced in September.

While federal officials said they were heartened by the findings, they emphasized the problem in chasing a virus that invents new defenses against immunization faster than vaccine manufacturers can design and produce modified shots. The government is confronting a crowded landscape of fast-moving Omicron subvariants that threaten to evade the population’s immunity from vaccinations and previous infections.

When the government first decided on the makeup of the new booster this past summer, it targeted BA.4 and BA.5, which together were by far the most prevalent versions of the coronavirus. But another fast-moving Omicron subvariant, BQ.1.1, could become dominant by Thanksgiving, said Dr. Stephen Hoge, the president of Moderna.

Dr. Hoge said that the company’s lab tests suggested that the new booster also produced robust levels of antibodies against that surging subvariant, although far fewer than against BA.4 and BA.5.

Dr. Hoge also cautioned that the BQ.1.1 tests were preliminary and involved only 40 participants.

Pfizer announced similar findings this month about the antibodies produced by its updated booster against BA.4 and BA.5. But while Pfizer’s study also showed that its shot could increase antibodies that defend against the subvariants, neither Pfizer nor Moderna could say whether its new booster resulted in less disease.

The Centers for Disease Control and Prevention is overseeing studies of the vaccines’ effectiveness, but those take significantly more time than studies of antibodies that form the body’s first line of defense. Results from the C.D.C. studies are not expected for months.

Public acceptance of the new boosters has been dismal: Only 10 percent of Americans ages 5 and older have received updated doses since the government began offering them in September. The lack of interest deeply worries federal and state health officials as winter approaches and people spend more time indoors and gather for the holidays.

Influenza shots are updated every year in much the same way as coronavirus vaccines are. But some outside scientists have questioned whether federal officials gambled correctly in buying billions of dollars’ worth of updated doses, suggesting that the previous booster might have protected equally well against severe disease and death.

The previous booster was called monovalent because it targeted the original version of the coronavirus; the new booster is called bivalent because it targets the original version as well as the BA.4 and BA.5 subvariants.

“We still do not have a single shred of evidence that the bivalent vaccine works better than the monovalent vaccine,” said Dr. Paul A. Offit, the director of the Vaccine Education Center at Children’s Hospital of Philadelphia and a member of the Food and Drug Administration’s panel of outside vaccine experts.

“The only evidence we have today has been neutralizing antibodies, and that hasn’t been particularly supportive,” Dr. Offit said. “You could argue we never needed to include these circulating strains, until a circulating strain arises that is resistant to protection against severe disease.”

While Moderna’s new findings are unlikely to resolve the scientific debate, Dr. Peter Marks, the F.D.A.’s top vaccine regulator, said “it is very encouraging to see the high degree of consistency” between Moderna and Pfizer’s findings. He said the bivalent boosters were the best existing shield against Covid-19 and urged everyone, especially older Americans, to consider getting the shot now.

Moderna said its researchers had studied levels of neutralizing antibodies in more than 800 people ages 19 to 89 who had received three shots: the original vaccination series and a first booster. One group of about 300 people received the original booster again, and the other group of 511 people got the updated booster.

Among those who had a prior infection, the company said, the updated shot produced about five times the level of antibodies as it did in those who received the old booster. Among those with no prior infection, the shot induced more than six times the level of antibodies as it did in those who had the old booster.

Those results seems to dovetail with Pfizer’s study of 76 participants older than 55, the results of which were released this month. The company said that the level of antibodies in people who had received its updated booster was four times as high as in those who had received the original one.

In Moderna’s study, Dr. Hoge said, the group that received the original booster twice and the group that received the new booster were demographically matched. But there was a difference in when they received their second boosters. Some outside scientists have questioned whether that factor could account for the higher antibody levels in people who received the updated booster in both Moderna’s and Pfizer’s studies.

Neither Moderna nor Pfizer “controlled for length of time after the last dose,” Dr. Offit said, adding, “There are a lot of problems with that.”

Dr. Hoge said a detailed analysis of the data showed that the difference in timing of the doses did not explain the difference in antibody levels.