Booster Dose of COVID-19 Vaccine Reduces Infection in Health Care Workers in Israel

Health care workers in Israel who received a booster dose of the Pfizer-BioNTech COVID-19 vaccine were significantly less likely to contract SARS-CoV-2 than those who received two doses, a recent study found.

The study, published in JAMA, included 1928 health care workers at Tel-Aviv Sourasky Medical Center Israel, between Aug. 8 and Sept. 20.

The median age was 44, and 71.6% of participants were women. All were immunocompetent and had received a two-dose series of the Pfizer-BioNTech COVID-19 vaccine at least one month before study enrollment, and 1,650 (85.6%) received a booster dose.

Overall, 44 participants contracted COVID-19 during the study period, including 39 who hadn’t received the booster dose and 5 who had, for an incident rate of 116 per 100,000 person-days compared with 12.8. Compared with those who only received two doses of the vaccine, the adjusted hazard ratio for SARS-CoV-2 infection after booster was 0.07 (95% CI, 0.02-0.20). Of the infections, 31 (70.5%) were symptomatic and 13 (29.5%) were asymptomatic. Infections among participants who weren’t boosted were more likely to be symptomatic than those among boosted participants (71.7% compared with 60% respectively).

“These findings are in line with the reduction in SARS-CoV-2-related hospitalizations across multiple age groups after booster administration reported in a large observational study in Israel, as well as with the reduction in SARS-CoV-2 infections observed after booster administration in persons older than 60 years reported in another Israeli nationwide study,” the authors, led by Avishay Spitzer, MD, wrote.

Booster recipients saw an increase in anti-S1-RBD IgG antibody levels starting five days after booster vaccination.

Investigators plan to continue surveillance of participants for a year after enrollment.

“These findings clearly indicate that providing another vaccine dose following a 2-dose initial series is associated with both improvement in the immunological response to the vaccine antigen and reduction in the risk of symptomatic and asymptomatic infection,” Anna Wald, MD, MPH, wrote in an associated editorial comment.

The US Centers for Disease Control and Prevention has approved emergency use authorization of the Pfizer-BioNTech booster for everyone aged 12 and older at least five months after the primary series.

“An important consideration is whether this vaccination is a booster dose or a third dose,” Wald wrote, noting that the longer interval between doses could result in a more durable immune response.

The study is among a growing body of research examining the efficacy of booster shots. A recent study from London showed that those who received three shots of Pfizer-BioNTech or AstraZeneca vaccines produced high neutralizing antibody titers against Omicron, Delta and Alpha variants.

In another study, investigators from the Ragon Institute of MGH, MIT and Harvard created a pseudovirus version of Omicron and determined that a third dose of an mRNA vaccine was required to protect against the variant.