Studies look at COVID-19 vaccine boosters; ACP, Annals forum tackles challenging clinical questions

Two Israeli studies showed that vaccine boosters reduced rates of infection and severe disease. Experts gathered for the seventh ACP and Annals of Internal Medicine virtual forum on COVID-19. The FDA authorized a monoclonal antibody for pre-exposure prophylaxis in certain patients.

The effects of a booster dose of the Pfizer-BioNTech vaccine were analyzed by two new studies, both conducted in Israel and published by the New England Journal of Medicine on Dec. 8.

The first study included 843,208 patients from one health system; all were 50 years of age or older and had received two doses of the Pfizer-BioNTech vaccine at least five months earlier. Ninety percent of the patients received a booster dose, and their rate of death due to COVID-19 was substantially lower than the 10% who had only received two doses (0.16 vs. 2.98 per 100,000 persons per day; adjusted hazard ratio, 0.10 [95% CI, 0.07 to 0.14]; P<0.001). The study was limited by its short duration (54 days), the study authors noted. However, at the time in Israel, “exposure to SARS-CoV-2 was substantial, and accordingly, the number of deaths due to Covid-19 was sufficient to show a significant association between the use of the booster and lower mortality,” they added. They concluded that the results should assist in decision making about the value of booster doses, especially in people ages 50 years and older, but said that “studies with longer-term follow-up periods to assess the effectiveness and safety of the booster are still warranted.”

The second study used government data on more than 4 million people 16 years of age or older who had received two doses of the Pfizer-BioNTech vaccine at least five months earlier. It compared rates of infection, severe illness, and death among those who had received a booster dose at least 12 days earlier to those who had not received a booster and to those who had received a booster three to seven days earlier. The rate of confirmed infection was lower in the booster group compared to the nonbooster group by a factor of 9.0 to 17.2, depending on the age of the patients, and compared to the early postbooster group by a factor of 4.9 to 10.8. Respective rate reductions in severe illness among the boosted patients were 17.9 (95% CI, 15.1 to 21.2) and 6.5 (95% CI, 5.1 to 8.2) in those 60 years of age or older and 21.7 (95% CI, 10.6 to 44.2) and 3.7 (95% CI, 1.3 to 10.2) among those 40 to 59 years of age. There weren't enough cases of severe illness in younger patients to provide a reliable ratio, the authors noted. “Understanding the protective effect of the booster dose in younger age groups is key for forming public health policy. Booster vaccination programs may provide a way to control transmission without costly social-distancing measures and quarantines,” they wrote.

An accompanying editorial praised the studies for providing “much-needed evidence of the effectiveness of the booster dose” but noted that in most settings “more is still to be gained by focusing on vaccinating the unvaccinated” as it “will ultimately lead to a greater reduction in severe disease and death.” An analysis of boosters in the U.S., published by MMWR on Dec. 10, found that 44.1% of people ages 65 years or older who were eligible for a booster received one in the period from Aug. 13 to Nov. 19.

In other COVID-19 news, ACP and Annals of Internal Medicine presented “COVID-19 Forum VII: Challenging Clinical Questions” on Wednesday, Dec. 8. The seventh edition of the forum series featured expert panelists addressing questions about COVID-19 that commonly face internists. The forum was moderated by Deborah Cotton, MD, MPH, FACP, deputy editor of Annals of Internal Medicine, with panelists Sabrina A. Assoumou, MD, MPH, assistant professor of medicine at Boston University School of Medicine; Judith S. Currier, MD, MSc, professor of medicine and division chief of infectious diseases for the University of California, Los Angeles (UCLA) department of medicine and director of the UCLA Clinical AIDS Research and Education Center; and Jeanne Marrazzo, MD, MPH, FACP, director of the division of infectious diseases and professor of medicine at University of Alabama at Birmingham School of Medicine. The full recording of the forum is available for replay and was published in Annals of Internal Medicine along with commentary by Christine Laine, MD, MPH, FACP, ACP Senior Vice President and Editor-in-Chief of Annals of Internal Medicine.

Finally, there were two COVID-19-related actions by the FDA last week. The agency issued an emergency use authorization (EUA) for AstraZeneca's Evusheld (tixagevimab co-packaged with cilgavimab) for pre-exposure prophylaxis of COVID-19 in certain patients, including those with moderate to severely compromised immune systems or a history of a severe adverse reaction to a COVID-19 vaccine and/or a component of those vaccines. Also, a modification to the EUA for the Pfizer-BioNTech vaccine authorized a booster dose in 16- and 17-year-olds at least six months after completion of primary vaccination.