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Omicron-specific boosters may not be necessary

Both Pfizer/BioNTech and Moderna have recently reported that they are starting clinical trials to test their newly developed Omicron-specific boosters, which may provide better protection against this immune-evasive, highly contagious variant. However, a new study conducted on primates (which is yet to be peer-reviewed) argues that there may not be significant benefits from updating the current vaccines to target specifically the Omicron variant.

A research team led by the National Institutes of Allergy and Infectious Diseases’ Vaccine Research Center has found that macaque monkeys boosted with the original Moderna vaccine had similar protection against Omicron-caused disease in the lungs as animals that received an updated, variant-specific booster. In fact, blood studies have shown that measurable immune responses, such as rises in neutralizing antibody levels, were mostly similar, regardless of the booster used.

According to senior author Robert Seder, the chief of the Cellular Immunity section at the Vaccine Research Center, these findings corroborate those of a previous study published in the journal Science last year, which showed that a booster shot based on the Beta variant of SARS-CoV-2 was not more effective against this particular variant than the original vaccines designed to target the wild-type virus that emerged in Wuhan in 2019.

“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. 

“The existing boosters provide improved (but imperfect) protection against infection,” added Angela Rasmussen, a virologist at the University of Saskatchewan’s Vaccine and Infectious Disease Organization. “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.” 

Moreover, according to Professor Seder and his colleagues, preliminary data suggests that an Omicron-specific vaccine may not be ideal if given on its own, since it might not generate the same level of cross-immunity as the original vaccines. Thus, if Delta or other variants make a comeback, or if new variants emerge, people may turn out be less protected by the Omicron-based vaccine than by the original ones.

Further research is needed to clarify whether these findings hold in the case of human subjects too, and whether other Omicron-specific vaccines, such as that developed by Pfizer/BioNTech have similar effects.

A pre-print of the study can be found on bioRxiv.

By Andrei Ionescu, Staff Writer

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