Third Dose of Pfizer-BioNTech COVID-19 Vaccine Confers Increased Protection in Elderly Adults

Following a booster shot, immunoglobulin G titers increased significantly in a study population aged 60 years and older.

Convincing evidence may help pharmacists persuade patients 60 and older to receive a third booster dose of the COVID-19 vaccine, according to a research letter published in JAMA.1

While the durability of the antibody response to the Pfizer-BioNTech vaccine in this patient population has yet to be determined, “the immune response to 2 doses of [the Pfizer-BioNTech vaccine] is lower in individuals aged 65 to 85 years,” compared with those between 18 and 55, according to Salomon M. Stemmer, MD, Davidoff Cancer Center, Rabin Medical Center, Belinson Hospital, at Tel Aviv University, and colleagues.

In a small study (n=97), researchers recruited study participants aged 60 and older from a pool of employees at the Rabin Medical Center and their families to receive a third booster dose of the Pfizer-BioNTech vaccine. Antispike (Anti-S immunoglobulin G (IgG) titer levels were recorded both before and 10 to 19 days after vaccination (August 4-12 and August 16-24, respectively). Seropositivity was defined as 50 arbitrary units (AU)/mL or higher.

Median participant age was 70 years (interquartile range, 67-74); 61% were women. Prior to the third dose, 97% of participants were seropositive, and the median titer level increased “significantly” after a third dose was administered, from 440 AU/mL to 24,468 AU/mL. Per investigators, all participants became seropositive.

No one variable was significantly associated with higher IgG titers, and no significant correlation between age and IgG titers was observed

Study limitations include the small sample size, the short follow-up period, and the lack of testing of cellular immunity and neutralizing antibody testing.

“This study found that a third dose…in adults aged 60 and older was associated with significantly increased IgG titers after 10 to 19 days, with no major adverse events,” Stemmer and colleagues concluded, noting that the research also adds serologic data “to clinical data on response to a third dose” in this patient population.

Reference

  1. Eliakim-Raz N, Leibovici-Weisman T, Stemmer A, et al. Antibody titers before and after a third dose of the SARS-CoV-2 BNT162b2 vaccine in adults aged ≥60 years. JAMA. Published online November 5, 2021. doi:10.1001/jama.2021.19885