The presence of neutralizing antibodies against omicron subvariants among a vaccinated cohort at one year after the first dose of vaccination in Malaysia.

This study assesses the neutralizing antibodies response to Omicron subvariants and examines factors associated with seropositivity in a vaccinated Malaysian cohort. It is a prospective cohort study, conducted between June 2021 and October 2022. Descriptive and binary logistic regression analyses were performed on 1,117 adults aged 18 and above. Among the subvariants, seropositivity rates were: BA.2 (81.9%), BA.1 (68.4%), and BA.4/5 (64.2%). Non-Malaysians had significantly higher odds of testing positive for BA.2 compared to Malaysians (OR: 8.009; 95% CI: 1.273-50.402). Recipients of AstraZeneca (OR: 3.955; 95% CI: 2.414-6.482) and CanSino (OR: 1.980; 95% CI: 1.047-3.743) vaccines had higher odds of BA.2 seropositivity compared to Pfizer recipients. For BA.4/5, individuals aged 60 and above had greater odds of seropositivity (OR: 1.751; 95% CI: 1.029-2.979) compared to those aged 18-39. Chinese ethnicity was associated with lower odds of seropositivity than Malay ethnicity across BA.1 (OR: 0.508; 95% CI: 0.350-0.736), BA.2 (OR: 0.570; 95% CI: 0.377-0.861), and BA.4/5 (OR: 0.671; 95% CI: 0.467-0.963). This study highlights that completing primary vaccination and booster doses remains critical to reducing severe COVID-19 outcomes, underscoring the need for ongoing surveillance and targeted strategies for vulnerable demographic and socio-environmental groups.