COVID-19 booster shots effective against severe illness from omicron: US studies

A booster dose of the Covid-19 vaccine significantly reduces a person's odds of hospitalization from the omicron variant, new research released Friday by the Centers for Disease Control and Prevention finds.

The three new studies from the agency are among the first to look at the vaccines' impact against omicron in the United States, which now accounts for more than 99 percent of new cases in the country.

The premise of the studies is that mRNA vaccine effectiveness (VE) in preventing Covid-19 decline because of waning of vaccine-induced immunity.

The first study looked at nearly 88,000 hospitalisations across 10 US states from August 2021 till now. The study found that while getting two vaccine shots was 57 per cent effective at preventing hospitalisations against Omicron, the booster dose provided better immunity at 90 per cent when it had been at least six months after the second shot.

The second study looked at the Covid-19 case count and the death rates in 25 US states from April 4 to December 25, 2021. The study showed that individuals who had taken the booster dose were less likely to get infected with Omicron.

The third study, involving CDC scientists, was published in medical journal Journal of the American Medical Association (JAMA). The study found that people who took the booster dose were 67 per cent less likely to develop symptomatic infection. However, two doses offered no significant protection against omicron when measured several months after completion of the original series, the study said.

Less than half of the U.S. population eligible for a booster dose has received one, according to CDC data.