The effects of heterologous immunization with prime‐boost covid‐19 vaccination against sars‐cov‐2

Coronavirus Disease 2019 (COVID‐19) pandemic, which is caused by the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), has become the global challenge. Reaching global herd immunity will help end the COVID‐19 pandemic. However, vaccine shortage and vaccine hesitancy are the obstacles to achieve global herd immunity against SARS‐CoV‐2. The current homologous vaccine regimen is experimentally switching to heterologous vaccination at several study sites. However, the reactogenicity of heterologous ChAdOx1‐S and mRNA vaccination against SARS‐CoV‐2 is still unclear. We have conducted a systematic review to summarize the current findings on the safety and immunogenicity of this heterologous vaccination and elucidate their implications against SARS‐CoV‐2. This systematic review was conducted by the guidelines of PRISMA. Articles were searched from PubMed and other sources (MedRixv and Google scholar) starting from 1 January to 5 September 2021. The search term was heterologous ChAdOx1‐S and BNT162b2 or mRNA‐1273 vaccination. Our review found that participants with ChA-dOx1/BNT162b2, ChAdOx1‐S/mRNA‐1273 or BNT162b2/ChAdOx1‐S did not have the serious ad-verse events seen with homologous vaccination. Participants with the heterologous regimen (ChA-dOx1/BNT162b2, ChAdOx1‐S/mRNA‐1273 or BNT162b2/ChAdOx1‐S), compared with those with two doses of ChAdOx1‐S, have shown a more robust immune responses against SARS‐CoV‐2, such as higher levels of responsive antibodies or increased numbers of spike‐specific T‐cells. Neverthe-less, these immune responses were slightly diminished in the recipients of BNT162b2/ChAdOx1‐S. Also, the safety study of heterologous ChAdOx1‐S/mRNA vaccination was based on small popula-tions. Further studies to enclose diverse categories, such as race/ethnicity or geography, may be necessary. Overall, the heterologous immunization with ChAdOX1‐S and the mRNA vaccine may improve the vaccine shortage related slow pace of reaching herd immunity, especially using the heterologous immunization with ChAdOx1‐S/BNT162b2.