Revival of the heterologous prime‐boost technique in COVID ‐19: An outlook from the history of outbreaks

Abstract Background The heterologous prime‐boost vaccination technique is not novel as it has a history of deployment in previous outbreaks. Aim Hence, this narrative review aims to provide critical insight for reviving the heterologous prime‐boost immunization strategy for SARS‐CoV‐2 vaccination relative to a brief positive outlook on the mix‐dose approach deployed in previous and existing outbreaks (ie, Ebola virus disease (EVD), malaria, tuberculosis, hepatitis B, HIV and influenza virus). Methodology and Materials A Boolean search was carried out to find the literature in MEDLINE‐PubMed, Clinicaltrials, and Cochrane Central Register of Controlled Trials databases up till December 22, 2021, using the specific keywords that include “SARS‐CoV2”, “COVID‐19”, “Ebola,” “Malaria,” “Tuberculosis,” “Human Immunodeficiency Virus,” “Hepatitis B,” “Influenza,” “Mix and match,” “Heterologous prime‐boost,” with interposition of “OR” and “AND.” Full text of all the related articles in English language with supplementary appendix was retrieved. In addition, the full text of relevant cross‐references was also retrieved. Results Therefore, as generally evident by the primary outcomes, that is, safety, reactogenicity, and immunogenicity reported and updated by preclinical and clinical studies for addressing previous and existing outbreaks so far, including COVID‐19, it is understood that heterologous prime‐boost immunization has been proven successful for eliciting a more efficacious immune response as of yet in comparison to the traditional homologous prime‐boost immunization regimen. Discussion Accordingly, with increasing cases of COVID‐19, many countries such as Germany, Pakistan, Canada, Thailand, and the United Kingdom have started administering the heterologous vaccination as the technique aids to rationalize the usage of the available vaccines to aid in the global race to vaccinate majority to curb the spread of COVID‐19 efficiently. However, the article emphasizes the need for more large controlled trials considering demographic details of vaccine recipients, which would play an essential role in clearing the mistrust about safety concerns to pace up the acceptance of the technique across the globe. Conclusion Consequently, by combatting the back‐to‐back waves of COVID‐19 and other challenging variants of concerns, including Omicron, the discussed approach can also help in addressing the expected evolution of priority outbreaks as coined by WHO, that is, “Disease X” in 2018 with competency, which according to WHO can turn into the “next pandemic” or the “next public health emergency,” thus would eventually lead to eradicating the risk of “population crisis.”