Two-Year Follow-Up of Humoral and Cellular Immune Responses to SARS-CoV-2 in Healthcare Professionals

Following the global spread of SARS-CoV-2, there was an urgent need for vaccine development to support immune protection. This study aimed to evaluate the impact of active and hybrid immunity on the durability of immunoglobulin G (IgG), neutralizing antibodies, and cellular immune responses over a two-year period.

This longitudinal study was conducted from February 2021 to December 2023 at the Public Health Institute in Ostrava, Czech Republic. Anti-S IgG was measured using ELISA (Euroimmun), neutralizing antibodies via an in-house virus neustralization test (VNT), and cellular immune response using the IGRA test (ELISA, Euroimmun). Participants also completed a questionnaire on demographics, COVID-19 history, symptoms, and vaccination. Statistical analysis included descriptive and non-parametric tests (Mann-Whitney U, Kruskal-Wallis) at a 5% significance level.

The cohort included 149 individuals, 97.3% of whom were vaccinated with Comirnaty (Pfizer/BioNTech). A total of 17% had confirmed infection prior to vaccination and showed up to two-fold higher neutralizing antibody levels (p < 0.001) within 2-6 weeks postvaccination. Postvaccination infection was reported in 35% of participants. Although antibody levels declined over the 2-100 week period, participants remained seropositive across all three parameters. Cellular immune response (interferon-γ) remained consistently high throughout follow-up.

The study demonstrates long-term durability of IgG and neutralizing antibodies and confirms durable cellular immunity up to two years postvaccination. Hybrid immunity significantly enhanced neutralizing antibody levels, supporting its added value in protective immunity against SARS-CoV-2.