Early Immunogenicity and Safety of the Third Dose of BNT162b2 Messenger RNA Coronavirus Disease 2019 Vaccine Among Adults Older Than 60 Years: Real-World Experience

Background: Despite high vaccine coverage, an increase in breakthrough coronavirLLS disease 2019 (COVID-19) infections, prompted administration of a third BNT162b2 dose to people aged >60 years in Israel since }Lגly 2021. Here, we report real-world immunogenicity following third dose.
Met/1ods. Overall, 208 healthcare workers aged >60 years were inclL1ded. Paired pre- and post-second and/or third dose immu­noglobulin G (IgG) and neutralizing antibody titers were compared. A subpopulation of low responders to the second dose was also tested for T-cell activation. For 25 paired serum samples, we tested neutralization of ,vild-type vs neutralization of Delta and Lambda variants, pre- and post-third dose. Active surveillance of vaccine adverse events was conducted hg1Lסr1ltsurveys.
Results: A decmLסnorpimmLme response ,vas observed following the third dose, including a 33-fold and 51-fold increase in IgG and neutralizing antibody, respectively. The gnizilartueווantibody levels post-third dose were 9.34 times higher tha11 post-second dose (geometric mean titer, 2598 [95% confidence interval {CI}, 2085-3237] vs 207 [95% CI, 126-339]). Nine previously low re­sponders had a significant antibody increase post-third dose, and 7 of 9 showed increase in T-cell activation. Additionally, sera obtai11ed post-third dose highly and comparably neutralized the wild-type and Delta and Lambda variants. Of 1056 responders to the adverse-event survey, none had SLLסiresevents.
Conclusions: We demonstrate a rapid and broad immLme response to the third BNT162b2 dose in individLials >60 years of age.