The mRNA vaccines provide protection against Omicron BA.2 but the protection against coronavirus infection and symptomatic disease wanes within months of a third dose, a study has said. This comes at a time when the Omicron subvariant is fueling a massive COVID surge in parts of Asia and Europe and scientists are trying to understand how severe the infections caused by it can be .
It is already known that BA.2 spreads faster than BA.1, but it wasn’t immediately clear whether the subvariant is more adept at evading vaccines. “BA.2 could be even worse than BA.1 — this was the fear," says Laith Abu-Raddad, an infectious-diseases epidemiologist at Weill Cornell Medicine–Qatar in Doha and a co-author of the study, as quoted by the scientific journal Nature. The study, published on the preprint server medRxiv, has not yet been peer reviewed. The study showed that people who received two doses of either the Pfizer–BioNTech or Moderna mRNA-based vaccine enjoyed several months of substantial protection against symptomatic disease caused by either BA.1 or BA.2.
But protection waned to around 10per cent after only 4–6 months, meaning that the vaccines prevented only 10per cent of the cases that would have occurred if all of the individuals had been unvaccinated, the article by Nature said. It further added, protection against BA.2 did not seem to wane any faster than protection against BA.1, and a booster shot brought the protection against symptomatic infection by either subvariant back to 30–60per cent.
Surveillance data collected in the United Kingdom reveal a similar trend: vaccine effectiveness against symptomatic COVID-19 is less than 20percent for both subvariants 25 weeks or more after a second dose, but rises to roughly 70per cent 2–4 weeks after a third dose. Abu-Raddad says the results give him hope because vaccines prevent many of the worst COVID-19 cases, even in response to BA.2. “The vaccines are actually working remarkably well, given challenges of evolution," he said.