Comparison of immune response parameters between homologous and heterologous COVID-19 vaccines: A scoping review

Abstract

It has been over 4 years since the emergence of the coronavirus disease 2019 (COVID-19) pandemic. This highly contagious respiratory infection has endangered the health of millions and significantly impacted healthcare systems and economies. Vaccines are believed to confer immunity against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19, reducing both the severity of infection and the spread of the virus. Within a short period, various COVID-19 vaccines were developed and extensively tested before being approved by the WHO for distribution and administration. Now, due to concerns about emerging new strains of the virus and limited vaccine availability, a heterologous vaccine strategy is being deployed. Therefore, this paper aims to conduct a scoping review of existing evidence to compare the immunogenicity of heterologous vaccines with homologous vaccines and determine which confers better immunity against COVID-19. A literature search was conducted across three electronic databases (Ovid MEDLINE, PubMed, and Scopus). The retrieved studies were screened for relevance and eligibility using the online platform Covidence. A total of 31 articles were shortlisted for data extraction and analysis. Among these, 21 were observational studies, and 10 were clinical trials. The analysis demonstrated that participants who received heterologous vaccination regimens generated higher levels of IgG antibodies against the spike protein of SARS-CoV-2, antibodies targeting the receptor-binding domain, and T-cell responses compared to those who received homologous vaccination regimens. Furthermore, heterologous vaccination produced higher titers of neutralizing antibodies against several variants of concern (VOC), including Alpha, Beta, Gamma, Delta, and Omicron. No severe vaccine-related adverse events were reported in these studies, and common local and systemic side effects were manageable. Overall, heterologous vaccination regimes induced strong humoral and cellular immunity, comparable to homologous vaccination regimes, with stronger neutralizing antibody activity against VOCs.