The first inactivated vaccine was against Polio virus, made by Jonas Salk, an American virologist. Since its introduction in 1955, the approach has continued to gain ground (Juskewitch et al., 2010). Inactivated vaccines contain pathogens previously destroyed using heat, chemicals, or radiation treatment (Rappuoli & Aderem, 2011; Seo, 2015). The mode of inactivation may affect the immunogenicity produced by the vaccine: for example, irradiated Listeria monocytogenes bacteria induced a greater protective T cell immune response in experimental mice than heat killed bacteria (Datta et al., 2006). With inactivated microbes, the vaccine is more stable and hence does not necessarily require freeze drying or refrigeration for storage and transportation.

Inactivated vaccines have been used for over a century and are safe compared to LAV (Sanders et al., 2014). However, they produce weaker immune responses and hence there is a need to coadminister adjuvants and/or additional booster doses to achieve the desired protective effect (Petrovsky & Aguilar, 2004). 38 Vaccinology and Methods in Vaccine Research Compared to LAV, they elicit mainly humoral immunity, with little to no cell mediated immunity (Lee & Nguyen, 2015). Inactivated vaccines are noninfectious , and licensed examples include viral and licensed examples target viral and bacterial diseases such as Hepatitis A, influenza, Polio, Rabies, tick-borne encephalitis, typhoid, cholera, plague, and pertussis. Many other experimental vaccines are at different stages of clinical development (Stauffer et al., 2006).

 During the inactivation process of the pathogen, care is taken to preserve important epitopes (e.g., targets for neutralizing antibodies) from denaturation  (Sanders et al., 2014). To produce high quality antigen, the production process of the vaccine must overcome challenges such as aggregate formation , protein cross linking, denaturation, and degradation (Delrue et al., 2012). BBIBP-CorV is an inactivated vaccine produced by Sinopharm against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Empirical data reveal that this vaccine produces strong neutralizing antibodies against SARS-CoV-2 in experimental animal models (Wang et al., 2020). The same report showed that immunized Rhesus macaques dosed intratracheally with BBIBP-CorV were protected against SARS-CoV-2 infection , providing rationale for evaluation of the vaccine in human clinical trials (Wang et al., 2020).

References

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6- Rappuoli, R., Bottomley, M. J., D’Oro, U., Finco, O., & De Gregorio, E. (2016). Reverse vacci nology 2.0: Human immunology instructs vaccine antigen design. The Journal of Experimental Medicine, 213(4), 469 481. Available from https://doi.org/10.1084/ jem.20151960, Epub 2016 Mar 28. Available from 27022144.

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