A third 'booster' dose of COVID-19 vaccine successfully raises antibody levels that neutralize the Omicron variant, according to laboratory findings from the Francis Crick Institute and the National Institute for Health Research (NIHR) UCLH Biomedical Research Center, published today (Wednesday) as a Research letter in The Lancet.

Researchers found that antibodies generated in people who had received only two doses of either the Oxford/AstraZeneca vaccine or the Pfizer/BioNTech vaccine were less able to neutralize the Omicron variant as compared to the Alpha and Delta variants.

They also found that antibody levels dropped off in the first three months following the second dose but that a third 'booster' dose raised levels of antibodies that effectively neutralize the Omicron variant.

In people who had received the Pfizer/BioNTech vaccine for all three doses, antibody levels against Omicron after a third dose were similar to those previously reached against Delta after only two doses. Overall, antibody levels were nearly 2.5x higher against Omicron after three doses compared to after two.

Higher levels of antibodies against the Omicron variant were also found in people who received two doses of either vaccine and also reported previously having COVID-19 symptoms, compared to those had not previously had COVID-19 symptoms.

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