3 Doses of COVID-19 Vaccine Neutralize the Omicron Variant

A third dose of the Pfizer-BioNTech or AstraZeneca mRNA COVID-19 vaccines produced sufficient neutralizing antibody titers against the Omicron variant.

A variant of concern now responsible for most new COVID-19 infections across the world, Omicron is known to be highly infectious. Laboratory findings from the Francis Crick Institute and the National Institute for Health Research UCLH Biomedical Research Center suggest that a booster shot is the best defense.

A study published yesterday in The Lancet found that 3 doses of the Pfizer-BioNTech (BNT162b2) or AstraZeneca (AZD1222) COVID-19 vaccines effectively neutralize the Omicron variant.

Dr. Emma Wall, a UCLH Infectious Diseases consultant and senior clinical research fellow for the study, said, “This new variant can overcome the immune blockade put in place by two vaccine doses, but thankfully following the third dose, neutralizing activity is robust in the vast majority of people. A third dose builds our defenses higher, making it harder for the virus to cause severe COVID-19.”

Investigators analyzed 620 blood samples from 364 study participants. Using robust high throughput viral neutralization assays, they tested the antibodies’ ability to stop COVID-19 variants from entering cells. They compared neutralizing antibody titers against Omicron with those against the Alpha and Delta variants.

Higher antibody titers signify vaccine efficacy and COVID-19 protection, and antibody levels after against Omicron were almost 2.5 times higher after a third vaccine than after the second.

People who received 2 doses of AstraZeneca or Pfizer-BioNTech and reported previously experiencing COVID-19 symptoms had higher antibodies than those who had no history of COVID-19 symptoms. This suggests that participants who experienced COVID-19 infection before or after 2-dose vaccination generated greater neutralizing antibody titers than those who did not.

The investigators concluded that a 2-dose vaccine series, especially of AstraZeneca, is insufficient to induce a strong neutralizing antibody response against Omicron. Participants who received a third dose of either vaccine, but of Pfizer-BioNTech in particular, produced consistently high neutralizing antibody titers against the Omicron, Alpha, and Delta variants.

It is important to note, however, that other studies have not found 3 doses of mRNA vaccination to effectively neutralize Omicron.

“Whilst levels of antibodies alone do not predict vaccine effectiveness, they are a very good indicator of protection against severe COVID-19,” the researchers said in a statement. “This study confirms that three doses of COVID-19 vaccine are essential to boost antibodies to quantifiable levels and maximize the amount of protection against severe disease and hospitalization.”