As the Omicron variant continues to spread, vaccine manufacturers are investing in clinical trials of vaccines tailored to the highly transmissible variant. However, a series of early animal studies, published in the journal Nature, suggest that Omicron-specific boosters offer no advantage over a third dose of the original vaccines.
Most studies involved only a small number of animals and none were peer-reviewed. But they offer early hints that a single dose of a personalized vaccine will make no difference in the fight against Omicron.
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“What we’re seeing in these preclinical studies in animal models is that a booster with a specific vaccine is not really better than a booster with the current vaccine,” explains David Montefiori, a specialist at Duke University Medical Center in North Carolina. , United States.
Since it was first identified in November, Ômicron has become the dominant variant globally. Its biology differs significantly from the original strain of SARS-CoV-2, on which currently approved vaccines are based. The differences may explain why three doses of existing vaccines are less effective against Omicron than against other variants.
Changes in the virus have forced manufacturers of widely used mRNA-based vaccines to develop Omicron-compatible formulations. Both Pfizer and Moderna announced in late January that they had begun clinical trials of specific vaccines against the variant.
However, while scientists await the results, these animal studies give no hope that the use of the updated vaccines will begin anytime soon.
Study 1 analyzed the immune responses of eight monkeys, which received three doses of the vaccine: two doses of the original Moderna and a booster of the same dose or a specific version against Omicron.
The authors found that monkeys vaccinated with any booster vaccine generated a broad antibody response against all variants of concern, including Omicron.
Study 2, done in mice, found that giving an Omicron-compatible booster after two doses of mRNA-based vaccine offered no more benefit than a standard booster.
The same study also looked at the Ômicron-specific vaccine in mice and found that they produced high levels of antibodies against this variant. But these antibodies had a limited ability to inhibit other important variants of Covid-19.
A third study, also performed on mice immunized with an Δmicron-compatible mRNA vaccine, reported similar results.
Finally, a fourth study investigated a ‘replicating RNA’ vaccine. In contrast to widely used mRNA vaccines, this one encodes a fragment of the virus and an enzyme to amplify the expression of that fragment. The scientists gave mice three doses of this vaccine: two doses based on the original strain, followed by a single Omicron-specific booster.
The third dose did not produce a heightened immune response against Omicron. But such a response was observed in mice that received one dose of vaccine based on the original strain and two doses of the specific vaccine against Omicron.
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