To Boost or Not to Boost (A Few More Takes)

As the FDA and CDC continue to assess the utility of COVID-19 booster vaccinations, three more studies expand our understanding of longer-term responses to full immunization with the Pfizer-BioNTech mRNA vaccine (BNT162b2).

Levin and colleagues performed monthly assessments of anti-spike IgG and SARS-CoV-2 neutralizing antibodies in 3808 immunized Israeli healthcare workers. They found that IgG antibodies peaked 4–30 days after the second dose, then consistently declined during the 6-month study period. Neutralizing antibody titers also fell, but the rate of decline was steeper from 1–3 months than 3–6 months. Decreases in both IgG and neutralizing antibodies were greater with older age, male sex, ≥2 comorbidities, and autoimmune disease or immunosuppression.

Chemaitelly and colleagues used a test-negative, case-control study design to evaluate vaccine effectiveness among 947,035 BNT162b2 recipients in Qatar. Effectiveness against SARS-CoV-2 infection peaked at 77% within the first month after complete vaccination, then progressively declined to 20% during months 5–7. In contrast, effectiveness against COVID-19 hospitalization and death attained at least 96% within the first month and did not drop throughout 6 months.

Tartof and colleagues assessed BNT162b2 effectiveness in 3,436,957 individuals in the Kaiser Permanente Southern California healthcare system. Throughout the 6-month study, 184,081 SARS-CoV-2 infections and 12,130 COVID-19 hospitalizations occurred. Effectiveness against infection fell from 88% during the first month to 47% after the fifth month. Effectiveness against hospitalization was 87% at 1 month and 88% at 5 months. Protection against infection with the Delta variant was similar to that against other variants within the first month (93% and 97%, respectively), then declined over time compared with other variants (53% and 67%; comparison not significant).