Inactivated Vaccines

Several inactivated vaccines are in current use in humans (Table ). The approach is chemical inactivation of the pathogen using formaldehyde or b-propiolactone. This approach usually ensures that the immunogenic features of the pathogen are retained. Production of inactivated vaccines requires large quantities of pathogenic material, with associated risks for the workers involved. Furthermore, it is essential tha  the inactivation process is complete, otherwise the pathogen will be introduced into the population. This occurred with early batches of the Salk polio vaccine, resulting in paralytic polio in a number of recipients.
The advantage over live, attenuated vaccines is that there is no risk of reversion to virulence. It is for this reason that the Salk vaccine is preferred over the Sabin polio vaccine in Scandinavian countries.
Inactivated vaccines generally produce significant antibody response but weaker cellular immunity, in particular cytotoxic T cell responses, than live vaccines. This is due mainly to the absence of microbial protein synthesis inside host cells. In turn, this leads to reduced or absent
cytosolic processing required for MHC class I presentation of peptides and poor activation of cytotoxic CD8+ T cells. Furthermore, the inability to replicate inside the host reduces immunostimulation and a need for more booster immunisations.

Table . The main types of bacterial and viral vaccines for use in humans