Background: The novel coronavirus is quickly spreading and mutating, putting the public health and lifestyle in shambles. The development and approval of mRNA vaccines came up as a breakthrough. The breadth of immune response after a single-dose vaccination in the already infected population is discovered for understanding the hybrid immunity and side effects associated with second dose. Administering a single-dose vaccine to the seropositive population can spare the doses for the population at higher risk.
Methods: PubMed, Web of Science, Google scholar, medRxiv and Cochrane library were explored to extract the original data on the efficacy of single-dose mRNA vaccines in seropositive subjects. The Cochrane risk of bias tool was used to assess the risk of bias in the studies.
Results: 6 studies evaluating the immunogenicity of single-dose mRNA vaccine were incorporated along with some observational studies and literature. These studies present promising evidence for administering only single-dose mRNA vaccine in seropositive subjects, providing biphasic immune response of higher breadth and duration.
Limitations: Most studies had a small sample size, did not correlate the results with higher age groups, with potential risk factors and the percentage of individuals who contracted breakthrough infections.
Conclusions: Single-dose mRNA vaccine can be immunogenic and protective enough for already seropositive population by increasing the number of Spike protein-specific memory B-cells. Vaccination schedules based on existing anti-body titers in such individuals can spare doses for vulnerable groups, especially when there is limited production and supply of vaccines worldwide
