Humoral anti-SARS-CoV-2 immune response for different strains after Sinovac-CoronaVac and Oxford/AstraZeneca (ChAdOx1-S) full vaccination on a healthcare population in Brazil

COVID-19, caused by the SARS-CoV-2 virus, is a global respiratory syndrome with high mortality rates. Vaccination is currently the only proven method to prevent the disease, although the role of lab data in assessing efficacy remains uncertain. This study aimed to assess spike-binding and neutralizing antibody levels following full vaccination with Oxford/AstraZeneca (ChAdOx1 nCoV-19) or CoronaVac in healthcare workers in southeastern Brazil. ChAdOx1 nCoV-19 and CoronaVac induced IgG antibodies against trimeric spike glycoproteins in 99.5% and 80.9% of individuals, respectively. Neutralizing antibodies were produced against two viral strains groups: variants group 1 (Wuhan-Hu-1, Alpha) and variants group 2 (Beta, Gamma) with neutralization rates of 88.3% and 78.2% for ChAdOx1 nCoV-19, and 68.1% and 48.9% for CoronaVac. No associations were found between neutralizing levels and comorbidities, age, or side effects. A positive correlation was observed between IgG antibody concentrations against trimeric spike glycoproteins and neutralizing levels for both vaccines and variants. These findings indicate that both vaccines induced reasonable levels of neutralizing antibodies against variants group 1, but only ChAdOx1 nCoV-19 maintained acceptable levels against a variant strain. The study suggests that evaluating vaccine responses to different pathogen strains can aid in managing healthcare workforce concerns and improve vaccine selection, thereby enhancing overall vaccination strategies.