The US Centers for Disease Control and Prevention says new research shows a booster dose of a coronavirus vaccine is 90 percent effective in preventing hospitalization due to infection with the Omicron variant.

The CDC on Friday released its study on the effectiveness of booster shots of the Pfizer and Moderna vaccines, based on data from medical institutions across the country.

It says that two doses of the vaccine were 81 percent effective against hospitalization after six months when the Delta variant was surging, and 57 percent when the Omicron variant became dominant.

However, a booster shot raised the effectiveness to 94 percent during the Delta wave, and to 90 percent during the Omicron surge.

Unvaccinated people aged between 50 and 64 are 44 times more likely to be hospitalized for COVID-19, compared to fully vaccinated and boosted individuals. The figure rose to 49 times among those aged 65 or older.

CDC Director Rochelle Walensky said the research demonstrates that protection against hospitalization is higher for those who have had booster shots. She urged people who are eligible to get their booster shot to get it as soon as possible.