Early efficacy data on bivalent boosters show that they work against infections

Zoom in / White House Chief Medical Adviser Dr. Anthony Fauci speaks with COVID-19 Response Coordinator Dr. Ashish Jha during a COVID-19 briefing at the White House November 22, 2022, in Washington, DC. Fauci spoke about the updated COVID-19 booster shots and encouraged people to get their vaccines. (Photo by Win McNamee/Getty Images)


The updated bivalent COVID-19 booster vaccine has increased protection against symptomatic disease compared to the original monovalent vaccine given just two months ago.

That’s the finding of a study released Tuesday morning by the Centers for Disease Control and Prevention, which offered the first clinical efficacy data for bivalent injection since its nationwide launch in September.

In adults the relative the protective efficacy of the bivalent vaccine against symptomatic infection ranged from about 30% to 56% of that of the monovalent vaccine, with the estimated relative efficacy being higher the longer it had been since a person’s last monovalent vaccination .

The real-world look at relative effectiveness was based on data from 360,000 people. The CDC researchers conducted the study between Sept. 14 and Oct. 11, when the BA.4/5 omicron subvariants and their subvariants dominated.

The study enrolled already exploited people in a national program aimed at increasing COVID-19 testing in areas of high social vulnerability. The study looked at people with COVID-19-like symptoms who entered partner pharmacies for COVID-19 testing. The researchers collected test results, as well as vaccination and infection history and other medical information. The study excluded people who were immunocompromised.

Of the 360,626 tests provided, 121,687 (34%) tested positive for COVID-19. Of the positive tests alone, 28,874 (24%) were among unvaccinated people, 87,013 (72%) were from people who had received two to four doses of monovalent vaccine but no bivalent booster dose, and 5,800 (5%) had received a bivalent booster dose.

Relative efficacy

For people aged 18 to 49 years, the relative vaccine efficacy (rVE) for a bivalent booster against a symptomatic infection was 30% compared to people who received two or more monovalent doses, with their vaccination most recently two or three months ago. rVE in this age group jumped to 56% compared to people with two extra monovalent doses, if the most recent dose was given eight months or more ago.

For the same comparisons in people aged 50 to 64, rVE ranged from 31% to 48%. And in those 65 years of age and older, rVE ranged from 28% to 43%.

Table showing relative vaccine efficacy by age, number of vaccine doses, and time since last vaccination.
Zoom in / Table showing relative vaccine efficacy by age, number of vaccine doses, and time since last vaccination.

“The results of this study show that bivalent boosters provide protection against symptomatic SARS-CoV-2 infection during circulation of BA.4/BA.5 and their stresses and restore the protection observed to decrease after vaccine reception monovalent, as demonstrated by the increase in rVE with a longer period of time since the last monovalent dose,” concluded the CDC authors. “All people should stay current on recommended COVID-19 vaccines, including bivalent booster doses, if it has been ≥2 months since the last monovalent vaccine dose.”

The study has limitations, including that it’s based on self-reported data, doesn’t account for different exposure risks, combinations of vaccinations and past infections, or different behaviors, such as mask wearing and social distancing. Vaccine estimates could also change with future SARS-CoV-2 variants.

But, overall, it shows that bivalent vaccines provide “additional protection against infection compared to previous vaccination with two, three or four monovalent vaccines alone.”

Fauci’s final message

At a White House press conference on Tuesday, top infectious disease expert Anthony Fauci stressed the need for more Americans to get their fall booster before the holidays and year-end rallies. Fauci’s White House appearance was likely his last in his current role as chief medical adviser to the president and leader of the NIH. He plans to retire later this year, ending an estimated decade-long career in federal research.

During her time at the podium today, she went through a point-by-point list of reasons to get vaccinated, including protection against serious disease, robust safety data, and the risk of future variants. Then he turned to the new data from the CDC.

The clinical efficacy data is “really quite good,” Fauci said.

“We know [the booster] It is safe. We know it’s effective. So, my message—and my last message, perhaps the last message I send you from this podium—is this: please, for your safety, for your family’s safety, get vaccinated for up-to-date COVID-19 not as soon as you are fit to protect yourself, your family and your community.”

Ashish Jha, White House COVID-19 response coordinator, echoed Fauci’s call, noting that the administration also today released plans for a six-week campaign to get more Americans vaccinated against COVID-19 this autumn, especially the elderly and nursing home residents.

We are “doubling down” efforts, Jha said. “The bottom line is: We need more Americans vaccinated.”

Currently, only 11.3% of eligible Americans have received a bivalent booster injection.

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