The new bivalent COVID-19 booster shots are up to 56 percent more effective at preventing symptomatic COVID-19 infection than the two original COVID-19 vaccines in adults ages 18 and up, according to new data from the Centers for Disease Control and Prevention.

The data, released Tuesday, is the first batch of effectiveness data from an official, large-scale study on the updated shots, which have been on the market since early October. The updated boosters target the BA.4 and BA.5 strain of the omicron variant, as well as the original strain. The original shots and first booster that Americans received targeted only the ancestral strain of COVID-19.

The data comes as the White House launches a six-week public education initiative to get Americans boosted ahead of the holidays. The push includes $350 million for community health centers and $125 million for organizations serving the elderly and disabled, as well as targeted ad campaigns.

Just 11 percent of Americans 5 and older have received an updated booster, although officials are not expecting a wave of hospitalizations and deaths similar to those in previous years.

Outgoing and longtime director of the National Institute of Allergy and Infectious Diseases Anthony Fauci encouraged all eligible Americans to get booster shots in the coming weeks to provide protection before the holidays. Tuesday likely marked Fauci’s last time at the White House podium before he retires at the end of the year after 38 years working at the National Institutes of Health.

“It is clear now, despite an initial bit of confusion, that the BA.4/5 bivalent booster, what we refer to as the updated vaccine, clearly induces a better response against BA.4/5 and the sub lineages of BA.4/5 than does the ancestral strain,” Fauci said. “So from a pure immunological standpoint, it looks quite good.”

Among people who received their last COVID-19 shot more than eight months ago, the updated boosters provided more protection against symptomatic disease compared to two monovalent shots.

Adults ages 18 to 49 received as much as 56 percent more protection, people ages 50 to 64 received as much as 48 percent more protection, and adults 64 and older received 43 percent more protection, the data found. More than 360,000 people participated in the study.

Just 13.1 percent of adults ages 18 and up have received the updated booster shot, according to agency data.

Fauci noted that the booster offers less protection against the XBB variant — which is currently circulating abroad — because that variant evades antibodies. But he also noted that antibodies are only one component of the body’s defense system, which includes memory B cells and T cells.

“It doesn’t fall off the map,” he said of the booster’s protection against XBB. “But it goes down. So you can expect some protection but not the optimal protection.”

Tempers flared during the briefing as several reporters attempted to shout questions about whether Fauci has done anything to personally investigate COVID-19’s origins, which has evolved into a serious question and a political flashpoint. Those questions were ignored, but Fauci reiterated his willingness to testify before House Republicans after they recaptured the majority in the midterm elections.

“If there are oversight hearings, I absolutely will cooperate fully and testify before the Congress when asked,” he said. “You may not know, but I have testified before the Congress a few hundred times over the last 40 years or so. So I have no trouble testifying. We can defend and explain and stand by everything we’ve said. So I have nothing to hide.”