Vaccine-induced humoral response against SARS-CoV-2 dramatically declined but cellular immunity possibly remained at 6 months post BNT162b2 vaccination

Highlights

• Both IgG against spike protein (SP IgG) and 50% neutralizing antibody markedly decreased at 6-month post-vaccination.

• SP IgG titer had a negative correlation with age and alcohol consumption, but cellular immunity did not correlate with these factors.

• SP IgG titer against the Delta strain was 60% of that against the original strain but increased to 90% in the subjects with breakthrough infection.

• Cellular immunity was observed despite the substantial decrease in antibody titer after vaccination, suggesting their sequential dynamics differed.

Abstract

To evaluate vaccine-induced humoral and cell-mediated immunity at 6 months after completion of two doses of BNT162b2 vaccination, immunoglobulin G against SARS-CoV-2 spike protein (SP IgG), 50% neutralizing antibody (NT₅₀), and spot-forming cell (SFC) counts were evaluated by interferon-γ releasing ELISpot assay of 98 healthy subjects (median age, 43 years). The geometric mean titers of SP IgG and NT₅₀ decreased from 95.2 (95% confidence interval (CI) 79.8–113.4) to 5.7 (95% CI 4.9–6.7) and from 680.4 (588.0–787.2) to 130.4 (95% CI 104.2–163.1), respectively, at 3 weeks and 6 months after the vaccination. SP IgG titer was negatively correlated with age and alcohol consumption. Spot-forming cell counts at 6 months did not correlate with age, gender, and other parameters of the patients. SP IgG, NT_50, and SFC titers were elevated in the breakthrough infected subjects. Although the levels of vaccine-induced antibodies dramatically declined at 6 months after vaccination, a certain degree of cellular immunity was observed irrespective of the age.