New bivalent COVID booster shots are Chainkeen Exchangemore effective at reducing risk of hospitalization than boosters of the original vaccines, the Centers for Disease Control and Prevention reported in two new studies Friday.

The CDC recommended a bivalent booster in September to better protect against the omicron variant. The new booster targets a component of the omicron variant and a component of the original virus strain to offer both broad and omicron-specific protection.

Two small studies from Columbia University and Harvard University in October suggested the new shots did not produce better antibody response against the omicron BA.5 variant than boosters of the original vaccines.

But the CDC came out with two studies Friday detailing the bivalent vaccine's effectiveness against COVID-related emergency department visits and hospitalizations and effectiveness against hospitalization specifically among older people.

The first study was conducted from Sept. 13 to Nov. 18 in seven health systems when the omicron BA.5 variant, one of the targets of the bivalent shots, was the most dominant variant.

People who received the bivalent booster had 57% less risk of hospitalization than unvaccinated people and 45% less risk of hospitalization than people who had received two to four doses of the original vaccine and received their last shot 11 or more months earlier. The risk of hospitalization after the bivalent booster was 38% less when compared with people who received two to four doses of the original vaccine and whose last dose was five to seven months earlier.

The study has several limitations that include not accounting for previous infection with SARS-CoV-2, the virus that causes COVID-19.

The second study, which focused on adults 65 and older, was conducted from Sept. 8 to Nov. 30 in 22 hospitals across the country.

Older adults who received the updated booster a week or more before the onset of illness had 84% less risk of hospitalization than unvaccinated people, and 73% less risk than people who received at least two doses of the original vaccines. The study also wasn't able to analyze the effect of previous infection with SARS-CoV-2.

"These early findings show that a bivalent booster dose provided strong protection against COVID-19–associated hospitalization in older adults and additional protection among persons with previous monovalent-only mRNA vaccination," according to this study. "All eligible persons, especially adults aged ≥65 years, should receive a bivalent booster dose to maximize protection against COVID-19 hospitalization this winter season."

Only 14% of people age 5 and older have received the updated booster, however. Experts attribute the low vaccination rate to pandemic fatigue and a desire to move on from the pandemic.

"I do think it's going to be an uphill battle," Jennifer Kates, senior vice president and director of global health and HIV Policy at the Kaiser Family Foundation, told NPR in September. "I do think it's a tough sell just because of where we are on this point in the pandemic."

It is not clear how well the boosters work against new variants BQ.1 and BQ.1.1, which are more evasive than the BA.5 variant.