Antibody titers of individuals vaccinated for COVID-19: A systematic review

An important preventive measure to mitigate the COVID-19 pandemic is vaccine implementation. In creating vaccines, evoking neutralizing antibody (NAb) production is the main objective. This review determines and compares the NAb titers produced by COVID-19 vaccine recipients based on the vaccine type and the manner of administration. This review includes published articles on studies with healthy participants with a minimum age of 18 years, without previous infections, and those who were given Emergency Use License (EUL) vaccines from WHO. Bias assessment was performed using the Cochrane Risk of Bias and the Newcastle- Ottawa Scale. In all the studies, 40.82% of the primary doses were viral vector platforms. For booster doses, 50% were mRNA platforms. Messenger RNA (mRNA) vaccines have higher titers as homologous than as heterologous vaccines. However, inactivated vaccines and viral vector vaccines have lower titers as homologous than as heterologous vaccines. Meanwhile, subunit vaccines lack data for their titers. Based on the antibody titers, homologous mRNA vaccines are more viral-protective than their heterologous counterparts. Heterologous inactivated and viral vector vaccines are more protective than homologous combinations, mainly when mRNA is the other type in those heterologous combinations. This is because mRNA vaccines elicit higher immunogenicity compared to other types.