Booster shots key in fight against Omicron, three US studies show

CHICAGO • Three US studies show that a third dose of an mRNA vaccine is key to fighting the Omicron coronavirus variant, providing 90 per cent protection against hospitalisation due to Covid-19, the US Centres for Disease Control and Prevention (CDC) has said.

The studies, led by the CDC, are among the first in the United States to look at the impact of booster doses against the fast-spreading Omicron variant, which now accounts for 99 per cent of all new Covid-19 cases.

Overall, they suggest that boosters helped protect against both infection and symptomatic disease. Adults aged 50 and older saw the most benefit from an extra dose of the vaccine made by Pfizer-BioNTech or Moderna.

"Protection against infection and hospitalisation with the Omicron variant is highest for those who are up to date with their vaccination, meaning those who are boosted when they are eligible," CDC director Rochelle Walensky said in a White House briefing on Friday.

As has been shown in other countries, vaccine boosters performed better against the Delta variant than Omicron, a highly mutated version of the Sars-CoV-2 virus that has been able to evade immunity from vaccines and prior infections.

One of the studies, published on Friday in the CDC's Morbidity And Mortality Weekly Report, looked at rates of hospitalisation, and emergency department and urgent care visits in 10 states between Aug 26 last year and Jan 5 this year. It found that protection from two doses of vaccine fell to 57 per cent in people who got their second shot at least six months earlier. Among those who received a booster, protection from hospitalisation and urgent care visits was 90 per cent.

Separately, researchers from Brazil and the University of Oxford said people who had two doses of the Covid-19 vaccine made by China's Sinovac Biotech should get boosted with a different shot to amp up their protection against Omicron.

The study, published on Friday in The Lancet, tested booster combinations on 1,240 people from Brazil aged above 18 years who had been immunised with Sinovac's shot, one of the most widely used globally, six months prior.

REUTERS, BLOOMBERG