Washington, D.C.—Now that the FDA has authorized a second COVID-19 vaccine booster shot for adults aged 50 years and older, the question for many is whether they actually should get one. Here is some background information that might help pharmacists guide them.

The FDA said it based its decision partially on a new Israeli study. In a preprint publication, researchers from Clalit Health Services and the Ben Gurion University of the Negev recount how, in response to the Omicron variant outbreak, Israeli authorities approved a fourth COVID-19 vaccine dose (second booster) for individuals aged 60 years and older who received a first booster dose 4 or more months earlier.

The retrospective, cohort study included all members of Clalit Health Services—aged 60 to 100 years—who were eligible for the second booster. The study team compared mortality due to COVID-19 among participants who received the second booster with those who received one booster dose.

With 563,465 participants meeting the eligibility criteria, 328,597 (58%) received a second-booster dose during the 40-day study period. While 92 second-booster recipients died due to COVID-19, that was the outcome in 232 participants who received one booster dose (adjusted hazard ratio 0.22; 95% CI 0.17-0.28), according to the researchers.

"This study demonstrates a substantial reduction in COVID-19 mortality by the second-booster in eligible subjects," the authors concluded.

Another Israeli study looking at a younger cohort was less conclusive. Correspondence in The New England Journal of Medicine discussed the open-label, nonrandomized clinical study in Israel where researchers assessed the immunogenicity and safety of a fourth dose of either BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna). Vaccines were administered 4 months after the third dose in a series of three BNT162b2 doses, and participants were 1,050 healthcare workers.

"After the fourth dose, both messenger RNA (mRNA) vaccines induced IgG antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor-binding domain and increased neutralizing antibody titers; each measure was increased by a factor of 9 to 10, to titers that were slightly higher than those achieved after the third dose, with no significant difference between the two vaccines," researchers reported, adding that the fourth dose did not lead to "substantial" adverse events—just the mild systemic and local symptoms seen with other COVID-19 vaccines.

The study pointed out, "A comparison of the initial response to the fourth dose with the peak response to a third dose did not show substantial differences in humoral response or levels of Omicron-specific neutralizing antibodies. Along with previous data showing the superiority of a third dose to a second dose, our results suggest that maximal immunogenicity of mRNA vaccines is achieved after three doses and that antibody levels can be restored by a fourth dose."

The Israeli researchers also observed low vaccine efficacy against infections in healthcare workers, as well as relatively high viral loads, which suggested that those who were infected were infectious. "Thus, a fourth vaccination of healthy young health care workers may have only marginal benefits," they explained. "Older and vulnerable populations were not assessed."

Other data, however, shows that adults aged 65 years and older remain the likeliest to get severely ill and die from SARS-CoV-2 infection. There also have been reports of older recipients being able to mount sufficient antibodies to provide protection after vaccination, similar to the problems with those who are immunocompromised.

At the same time, a Mayo Clinic study found that the chance of ending up hospitalized with COVID-19 is exceptionally low for people who have immunity, either through vaccination or prior infection, according to a new study.

In fact, the report in Clinical Infectious Diseases pointed out that fewer than 1 in 1,000 people who have been vaccinated or previously infected with COVID-19 were hospitalized with a new breakthrough infection.

"In the general primary care patient population, those who have been vaccinated have very low risk of subsequent hospitalization for breakthrough COVID-19," explained lead author Benjamin Pollock, PhD, a researcher in the Mayo Clinic Robert D. and Patricia E. Kern Center for the Science of Health Care Delivery. "Our study shows that while it can and does happen that these occurrences are extremely uncommon."

Researchers used a longitudinal study of 106,349 adult primary care patients at Mayo Clinic in Rochester, Minnesota, who tested positive for COVID-19, and/or were vaccinated for COVID-19. They determined that only 69 of those patients were hospitalized with a breakthrough COVID-19 infection.

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.