The risk of hospitalization for COVID-19 among older Americans is far higher for those who are unvaccinated than for those who are fully vaccinated and have had a booster shot, new government data shows.

The differences were stark: In December, unvaccinated people 50 and older were 17 times more likely to be hospitalized with COVID-19 than those who had completed the initial immunization series, but hadn’t yet received a booster, according to statistics published Thursday on the U.S. Centers for Disease Control and Prevention’s website.

Among those ages 50-64, unvaccinated people were 44 more times to be hospitalized with COVID-19 than those who were fully vaccinated and had a booster shot, the data showed.

The risk difference was even greater among seniors: Among Americans over 65, the chances of hospitalization for COVID-19 was 49 times higher for those who were unvaccinated than for those with full vaccination and a booster.

The findings suggest that booster shots provide older Americans with a significant added level of protection.

This is the first real-world data on the impact of COVID vaccine boosters in the United States, and adds to research from other countries showing that boosters reduce the risk of severe illness and hospitalization, especially among older adults.

When weighing booster shots for all American adults, scientific advisers to the U.S. Food and Drug Administration and the CDC repeatedly bemoaned the lack of booster shot data specific to the United States. At that time, they only had data from Israel to analyze.

But there are differences between the two countries—most notably in the way Israel defines severe illness—that made it hard to assess the relevance of Israeli data for Americans, the advisors said at the time.

The CDC now recommends booster shots for everyone ages 12 and older, to be given five months after getting two doses of the vaccines made by Pfizer and Moderna, or two months after a single dose of the Johnson & Johnson vaccine.

On Friday, the agency is expected to release more recent data on the effectiveness of vaccines and boosters against the Omicron variant.