Researchers at the Centers for Disease Control and Prevention released data Friday indicating that the newer two-strain Covid booster shots provide substantial protection against illness and hospitalization, even in the previously vaccinated.

The Food and Drug Administration said Friday that it will convene an advisory hearing next month to discuss what vaccines should look like going forward, including whether people who have never received any Covid vaccines should receive the bivalent as their first.

Earlier this year, the FDA and the CDC authorized and recommended new versions of the booster shots with far less evidence from clinical studies that they prevented severe disease, in a bet that matching the vaccines to currently circulating variant strains of the SARS-CoV-2 virus that causes Covid would provide better protection. The new results bolster the case that these new shots, called bivalent boosters because they include both the original strain of the virus and a newer Omicron strain, are effective at preventing disease.

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The most compelling data were from a study of 798 patients who were 65 years old or older, putting them at highest risk of Covid. Those patients who received one dose of the booster in addition to at least two shots of the original, monovalent vaccines were 84% less likely to be hospitalized due to Covid than the unvaccinated. They were also 73% less likely to be hospitalized than those who had received two or more doses of the monovalent vaccines. The study included patients older than 65 admitted to a network of 22 hospitals in 18 states that are part of the Investigating Respiratory Viruses in the Acutely Ill Network, or IVY from Sept. 8 through Nov. 30.

Data from a separate study in adults aged 18 or older found that the new booster shot resulted in fewer patients turning up at emergency departments or urgent care centers. Patients who received the bivalent booster were 57% less likely to seek this type of care than those who were unvaccinated, 38% less likely than those who received their monovalent shot five to seven months before infection, and 45% less likely than those who received their last monovalent dose 11 months earlier or more.

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That study included 9,000 case patients and 69,294 controls presenting at a network of urgent care centers and hospitals known as VISION.

One of the bivalent shots is produced by Pfizer and BioNTech, and the other by Moderna. Those companies also make the original monovalent vaccines.

The studies have limitations. They are not randomized controlled trials, the gold standard of medical evidence, but comparisons of databases that the CDC uses to track vaccine effectiveness in the real world. Still, they appear to show substantial benefits to getting a bivalent booster over the original vaccine course.

The studies do not seem, however, to answer the question of whether it was the right call to move to the newer boosters, simply because there are no people who received a booster of the original vaccine in the same time frame.

Few Americans — less than 15% — have elected to receive the new boosters, a fact some experts say has contributed to the virus’ toll, particularly among older adults. There are also debates about whether booster efforts should focus on the whole populace, or on people, like older adults, who are at the highest risk.

In authorizing the bivalent boosters, FDA chose a path similar to flu shots, but unlike previous Covid boosters. The agency did not require human studies before making the new vaccine, instead relying on mouse models showing they significantly increased neutralizing antibodies against circulating strains of the virus.

Afterwards, data slowly trickled out on how well the shots actually boosted antibodies — first from academics, and then from clinical trials run by Pfizer and Moderna.

Two academic studies from prominent infectious disease researchers, Daniel Barouch, of Beth Israel Deaconess Medical Center, and David Ho, of Columbia University, cast doubt on whether the new shots induced more antibodies against circulating strains than old ones. But studies from the University of Texas and at Emory University, and ultimately the trials from Pfizer and Moderna, suggested the opposite. The debate was not whether the new boosters would grant protection, but whether they would be better than the original shots.

An observational study put out by the CDC last month suggested that the boosters reduced the odds that an adult would get a symptomatic infection, compared to receiving no booster at all.

The new data, on study’s authors say, suggest “important incremental benefit for persons eligible to receive a bivalent vaccine booster.” The challenge for government officials may be getting that message to the public — and convincing Americans to roll up their sleeves one more time.

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