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A new study conducted in primates suggests there may not be a benefit from updating Covid-19 vaccines to target the Omicron variant at this time.

The work, by scientists at the National Institutes of Allergy and Infectious Diseases’s Vaccine Research Center, shows that animals boosted with the original vaccine had similar levels of protection against disease in the lungs as did primates that received an updated booster based on the Omicron strain. The work was done with Moderna’s licensed vaccine and a booster shot based on the Omicron variant.


Study of blood from the animals showed that many of the measurable immune responses — rises in neutralizing antibody levels, for instance — were not substantially different, regardless of which booster shot they were given.

“Therefore, an Omicron boost may not provide greater immunity or protection compared to a boost with the current [Moderna] vaccine,” the researchers concluded.

The study was posted to a preprint server on Friday. It has not yet gone through peer review.


Senior author Robert Seder said the findings are similar to those of a study the group conducted last year, when researchers compared a booster shot based on the Beta variant to the existing vaccine. In that case as well, data generated in primates suggested boosting with the original vaccine was as effective at protecting the lungs as was a booster based on the Beta variant. (That variant of concern, first spotted in South Africa, did not spread globally.)

“These data would suggest that the initial imprinting of the initial vaccine generated B cells that … when you give them a boost six or nine months later, they’re cross-reactive to Omicron or Beta or Delta,” said Seder, chief of the cellular immunity section at the Vaccine Research Center.

Seder said studies will need to be done in people to ensure the findings hold, but at this point it doesn’t appear that the vaccine strain needs to be updated. “From the company’s standpoint, I don’t know how they view this,” he said. “But I think these data are fairly clear.”

In an emailed comment, Moderna said it will continue to work to keep pace with the virus.

“We believe protection against variants of concern will be important, especially as we look ahead to the fall of 2022,” the company said. “We will continue to follow the science and epidemiology of SARS-CoV-2 and potential new variants of concern. We are committed to remaining ahead of the virus as it evolves.”

Moderna CEO Stéphane Bancel has announced plans to develop a three-in-one annual shot that would target SARS-2, influenza, and respiratory syncytial virus or RSV, a virus that causes cold-like illness in many adults but which can be dangerous in babies and older adults.

John Moore, a virologist at Weill Cornell Medical College in New York City, said these findings, combined with the earlier work on the Beta-based booster, suggest the current vaccine is generating cross-protective responses.

“Accordingly, changing to an Omicron boost may well be unnecessary — literally more trouble than it’s worth,” Moore said in an email. He added that he expects human trials being conducted by Pfizer and Moderna to test an Omicron-based booster will show the same thing. “What we have is likely to be important for formulating future policies.”

Angela Rasmussen, a coronavirus virologist at the University of Saskatchewan’s Vaccine and Infectious Disease Organization, concurred, though she cautioned that these findings are based on a small number of animals. “I think we’ll have to wait for human trial results to see if there’s a difference in the real world at population scale,” she said.

Still, Rasmussen said she wasn’t surprised by the results, saying they are consistent with what has been seen during the Omicron wave.

“The existing boosters provide improved (but imperfect) protection against infection,” she said in an email. “Based on these data, it doesn’t look like an Omicron-specific booster would improve that all that much. Certainly both booster formulations provide significant protection compared to the controls, but it may not be necessary to have Omicron-specific boosters.”

The paper notes that data have begun to emerge that suggest that an Omicron-based vaccine would not be ideal if given on its own, because Omicron may not generate the same level of cross-protection as the original vaccine strain does. If the virus continues to evolve from Omicron, at some point using it in the vaccine may make sense, Seder said. But if Delta or other earlier versions of the virus made a comeback, people might not be as well-protected by an Omicron-based vaccine as they are by the current version.

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