Efficacy of Heterologous Immunization and Hybrid Immunity as Vaccination Strategies During the COVID-19 Pandemic: A Narrative Review of the Literature

Background: During the COVID-19 pandemic, achieving herd immunity became the main objective to minimize mortality, severe COVID-19 and the emergence of new SARS-CoV-2 variants. New vaccination strategies, heterologous immunity and hybrid immunity, emerged as partial solutions to the health emergency. Aim: To conduct a thematic review on the efficacy of new vaccination strategies against SARS-CoV-2/COVID-19 and their potential use in public health. Methods: A selective and strategic literature search was conducted in PubMed, MEDLINE, Embase, Web of Knowledge, Scopus, CINAHL, LILACS, ScieELO and Cochrane databases. The terms ‘COVID-19, SARS-CoV-2, Vaccines, Heterologous immunity, Hybrid immunity’; and Boolean operators (AND, OR, NOT) were used. In the English language, during the years 2020 - 2024. Results and conclusions: Novel immunisation strategies have been shown to be effective and safe for the control of SARS-CoV-2 infection and its triggering pathology COVID-19. Heterologous immunity can be used to supplement and boost immunisation schemes against SARS-CoV-2. Mixing two platforms exerts a synergism in the immune response that provides protection against SARS-CoV-2 strains. The immunological mechanisms underlying the observed benefits are still under investigation. Hybrid immunity was also shown to be effective and safe. Prior infection and subsequent vaccinations provide a humoral response capable of neutralizing SARS-CoV-2 variants. This new knowledge serves as a basis for responding to future health emergencies associated with immunopreventable pathologies. Recent evidence of developments in the field of vaccinology.