This study assesses antispike (anti-S) IgG antibody titers before and after a third BNT162b2 dose (booster) in individuals aged 60 years and older in Israel.

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ObjectiveTo evaluate the durability of response 3 months after the third BNT162b2 vaccine in adults aged 60 years and older.DesignProspective cohort study.SettingSingle tertiary centre.ParticipantsHealthcare workers/family members aged ≥60 years old who received the third BNT162b2 dose.InterventionsBlood samples were drawn immediately before (T0), 10–19 days (T1) and 74–103 days (T2) after the third dose.Primary and secondary outcome measuresAnti-spike IgG titres were determined using a commercial assay and seropositivity was defined as ≥50 arbitrary units (AU)/mL. Neutralising antibody titres were determined at T2. Adverse events, COVID-19 infections and Clinical Frailty Scale (CFS) levels were documented.ResultsThe analysis included 97 participants (median age, 70 years (IQR, 66–74), 58% CFS level 2). IgG titres, which increased significantly from T0 to T1 (median, 440 AU/mL (IQR, 294–923) and median, 25 429 AU/mL (IQR, 14 203–36 114), respectively; p<0.001), decreased significantly by T2, but all remained seropositive (median, 8306 AU/mL (IQR, 4595–14 701), p<0.001 vs T1). In a multivariable analysis, only time from the second vaccine was significantly associated with lower IgG levels at T2 (p=0.017). At T2, 60 patients were evaluated for neutralising antibodies; all were seropositive (median, 1294 antibody titres; IQR, 848–2072). Neutralising antibody and anti-spike IgG levels were correlated (r=0.6, p<0.001). No major adverse events or COVID-19 infections were reported.ConclusionsAnti-spike IgG and neutralising antibody levels remain adequate 3 months after the third BNT162b2 vaccine in healthy adults aged ≥60 years, although the decline in IgG is concerning. A third dose of vaccine in this population should be top priority.