Determinants of neutralizing antibody responses after SARS-CoV-2 infection in vaccinated and non-vaccinated individuals

SARS-CoV-2 infection induces neutralizing antibodies (nAbs) which are essential for clearing the virus and protecting against severe disease. We aimed to compare nAb titers between vaccinated and non-vaccinated subjects and evaluate factors associated with nAb responses. A total of 194 individuals recovered from SARS-CoV-2 infection (97 vaccinated and 97 non-vaccinated against SARS-CoV-2) in Lahore were enrolled in our study. The type of vaccine as well as pertinent clinical and demographic variables of study participants were recorded. nAb titers were measured using Electrochemiluminescence Immunoassay. Among 194 participants, 61% were male, with a median age of 31 years (IQR: 25–43). Half of the participants were vaccinated, with Sinovac being the most administered vaccine. The median nAb titer was 71 (IQR: 15–250). No significant differences in nAb titers were observed between vaccinated and non-vaccinated individuals ( p = 0.15). In multivariable analysis using log-transformed titers, age was positively associated with antibody levels (β = 0.02, p = 0.012), whereas male gender (β = −0.98, p < 0.001) and presence of comorbidities (β = −0.85, p = 0.003) were associated with significantly lower titers. Other factors, including disease severity, body weight and clinical course, were not significantly associated with antibody levels. In this cohort of COVID-19 recovered individuals, nAb responses were not significantly associated with vaccination status or vaccine type. Older age was associated with higher antibody levels, whereas male sex and the presence of comorbidities were associated with lower titers. Given the cross-sectional design and heterogeneous vaccination histories, these findings should be interpreted as associations rather than evidence of causal effects. Prospective longitudinal studies are needed to better characterize post-infection antibody dynamics.