Recombinant Poliovirus type 1 Capsid protein (strain Sabin)

Poliovirus, the pathogen of polio, destroys motor neurons in the central nervous system, leading to paralysis and even death. Of these, wild-type poliovirus type 1 remains endemic in Afghanistan, Nigeria and Pakistan, while wild poliovirus type 2 has not been detected worldwide since 1999. Poliovirus, with its small size and simple structure, is a human enterovirus that has been extensively studied. It enters human cells by binding to the immunoglobulin-like receptor CD155 and by endocytosis, and is more readily translated upon entering the cell because of its positive-stranded RNA genome. Poliovirus hijacks cells by producing proteases that disrupt cap-binding proteins, and translation of viral mRNAs is not dependent on the cap structure, so host cell translators are completely dedicated to the production of viral proteins. Inhibition of the host translation system contributes to virus-specific protein synthesis, ultimately leading to the production of a single viral long-chain protein, which in turn is cleaved by internal proteases into 10 viral proteins.

Poliovirus is considered to be one of the most rapidly evolving viruses, with an estimated total nucleotide substitution rate of approximately 0.01 substitutions per site per year in the capsid coding region. The evolution of this virus, like that of normal positive-stranded RNA viruses, is based on polymerase error-induced point mutations and recombination, followed by selection of mutants due to limitations in transmission routes. Simultaneously with the increase in mutations, this in turn produces mutant enrichment.

The final strategic plan for the global polio eradication campaign is currently in its final stages, and vaccination policy reforms are being implemented to ensure that the eradication campaign is completed and sustained. Polio vaccines currently in use include oral polio vaccine (OPV) and inactivated polio vaccine (IPV). Among them, OPV is the preferred vaccine, which is relatively inexpensive, easy to administer, induces gastrointestinal mucosal immunity in the body, and contributes greatly to the control of the incidence and prevalence of poliomyelitis. However, the potential exists for OPV to cause vaccine-derived poliovirus to circulate and regain virulence. IPV induces effective humoral immunity, allowing vaccinated individuals to fight the disease, but does not elicit sufficient mucosal immunity and prevent the proliferation of wild viruses in the intestinal tract, and is less efficient than OPV for protection in a population.

Figure 1. Global clinical trials of poliovirus vaccines in infants, children and adults
(Source: Connor RI, et al. 2022)