Moderna formulates its vaccine against Omicron. Instead of containing the historic SARS-CoV-2 protein S mRNA, it contains that of the Omicron variant. A small pre-published study tests its effects on immunity in an animal model. According to initial results, the Omicron booster is no more effective than its predecessor.
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Pfizer and Moderna are currently working on a version “ Omicron ” of their vaccine at mRNA respective. The idea is to strengthen theimmunity by injection of a vaccine developed according to the majority SARS-CoV-2 variant. From clinical tests are underway to verify the relevance of this approach. While waiting for these results, a pre-published study on BioRxivoffers a first insight into the effect of an Omicron-specific booster on the immunity of primates not human.
An Omicron booster as effective as the classic formula
The researchers of National Institute of Health vaccinated eight rhesus macaques according to the protocol applied to humans: two doses of Moderna, spaced four weeks apart. Nine months later, four monkeys received a third dose of Moderna and four others a special Omicron dose. Both recalls reactivated the antibody specific to SARS-CoV-2 which had become almost undetectable, nine months after the primary vaccination. But the Omicron booster did not confer greater immunity or protection against Omicron than the historical vaccine formulation. On the other hand, 70 to 80% of B lymphocytes are cross-reactive, that is to say specific for both the historical SARS-CoV-2 and Omicron. Again, the Omicron booster did not stimulate cell-specific B cell proliferation. this variant.
These results are consistent with what is called antigenic original sin. The immune system has a memory of all past infections. When he meets the same pathogenic or a close variant, it reactivates this memory to protect itself. It is through this mechanism that people infected with a coronavirus (OC43) also have pre-existing protein S-specific antibodies. Although different, OC43 and SARS-CoV-2 belong to the same family of virus and are close enough to stimulate the same set of memory B cells. Conversely, SARS-CoV-2 infection appears to reactivate OC43-specific antibodies. This is also what scientists have observed in monkeys. The immune response induced by the special Omicron booster is based on immune memory built up over infections with other coronaviruses.
” Therefore, an Omicron boost may not provide greater immunity or protection compared to a boost with the current mRNA-1273 vaccine. “, write the researchers in their publication. The Omicron booster is as effective as a classic Moderna booster, which gate so 90% hospitalization protection, according to recent figures from the CDC. The results observed here, not yet submitted for peer review and obtained on a handful of monkeys, are not robust enough to extrapolate them to humans.
If the results of ongoing clinical trials agree, then design a vaccine specific to Omicron may not be useful at this time. On the other hand, the researchers believe that if Omicron establishes itself as the majority variant over the long term, it may be interesting to vaccinate the immunologically naive population with a variant-specific formula. But this strategy needs to be further refined: Importantly, it would need to be established that a change in vaccine design Covid-19 to match the current dominant variant would not compromise responses against variants that may be antigenically distant from Omicron “, he concludes.
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