A third dose of vaccine has been shown to effectively neutralise the Omicron variant of covid-19, according to researchers.
Research led by UCLH, UCL and the Francis Crick Institute found that the booster dose successfully stimulates antibody levels that neutralise Omicron. Details of the study were published in The Lancet this week.
UCLH researchers stated 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 neutralise the Omicron variant 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 neutralise 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 2.5 times higher against Omicron after three doses compared to after two.”
The findings have been submitted to the Genotype-to-Phenotype National Virology Consortium (G2P-UK), the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) and the Joint Committee on Vaccination and Immunisation (JCVI).
Researchers used robust high throughput viral neutralisation assays, developed at the Francis Crick Institute, to test the ability of so-called ‘neutralising antibodies’ to block entry of the virus into cells, against different variants of SARS-CoV-2, including Omicron.
Healthcare workers and staff from the institutions mentioned contributed to the Legacy study by donating regular blood and swab samples so that researchers can track changing risk of infection and response to vaccination.
Dr Emma Wall, UCLH infectious diseases consultant and senior clinical research fellow for the SARS-CoV-2 Legacy study, said: “People who have queued outside vaccinations centres should be reassured that a vaccine booster is the best way of protecting them from Omicron.
“And for people who haven’t yet had a booster or even a first dose, it’s not too late. This new variant can overcome the immune blockade put in place by two vaccine doses, but thankfully following the third dose, neutralising activity is robust in the vast majority of people. A third dose builds our defences higher, making it harder for the virus to cause severe COVID-19.”
UCLH notes that although antibody levels alone do not predict vaccine effectiveness, they are “a very good indicator of protection against severe COVID-19.” It adds that the study confirms that three doses of COVID-19 vaccine are essential to boost antibodies to quantifiable levels and maximise protection against severe disease and hospitalisation.
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