Abstract
The oral poliovirus vaccine (OPV), which prevents person-to-person transmission of poliovirus by inducing robust intestinal immunity, has been a crucial tool for global polio eradication. However, polio outbreaks, mainly caused by type 2 circulating vaccine-derived poliovirus (cVDPV2), are increasing worldwide. Meanwhile, immunodeficiency-associated vaccine-derived poliovirus (iVDPV) is considered another risk factor during the final stage of global polio eradication. Patients with primary immunodeficiency diseases are associated with higher risks for long-term iVDPV infections. Although a limited number of chronic iVDPV excretors were reported, the recent identification of a chronic type 2 iVDPV (iVDPV2) excretor in the Philippines highlights the potential risk of inapparent iVDPV infection for expanding cVDPV outbreaks. Further research on the genetic characterizations and molecular evolution of iVDPV2, based on comprehensive iVDPV surveillance, will be critical for elucidating the remaining risk of iVDPV2 during the post-OPV era.
Highlights
Trivalent oral poliovirus vaccine (OPV), which contains three live-attenuated poliovirus serotypes, was a crucial tool for global polio eradication by inducing a high level of intestinal immunity to prevent person-to-person transmission of poliovirus in communities. Due to their intrinsic genetic instability, the OPV strains can evolve into more neurovirulent revertants in the vaccinated individuals and transmit in communities, which are occasionally associated with polio outbreaks known as circulating vaccine-derived polioviruses (VDPV; cVDPVs) [3,5,6,7,8,9]
VDPVs are categorized by the source of samples and epidemiological information, including cVDPVs identified in person-to-person transmission in the community, immunodeficiency-associated vaccine-derived poliovirus (iVDPV) isolated from persons with primary immunodeficiency (PID), and ambiguous VDPVs indicating neither cVDPV nor iVDPV [12,18,19,20]
A codon-by-codon comparison throughout the VP1 region using SNAP [54] showed that the rates of non-synonymous substitutions in the iVDPV strains were higher than those in cVDPV2 (Figure 2). These data suggest that the molecular evolution of the capsid proteins associated with phenotypic determinants, including antigenic sites, is more likely to occur in the iVDPV strains than in the cVDPV strains, especially for long-term iVDPV infections
Summary
The Global Polio Eradication Initiative has completely eliminated 2 of 3 serotypes of wild polioviruses worldwide with extensive immunization with poliovirus vaccines, the Sabin oral poliovirus vaccine (OPV), and Salk inactivated poliovirus vaccine (IPV) [1]. Trivalent OPV (tOPV), which contains three live-attenuated poliovirus serotypes (usually Sabin 1, 2, and 3 strains), was a crucial tool for global polio eradication by inducing a high level of intestinal immunity to prevent person-to-person transmission of poliovirus in communities. Due to their intrinsic genetic instability, the OPV strains can evolve into more neurovirulent revertants in the vaccinated individuals and transmit in communities, which are occasionally associated with polio outbreaks known as circulating vaccine-derived polioviruses (VDPV; cVDPVs) [3,5,6,7,8,9]. We discuss the future challenges in elucidating the molecular evolution and characterization of iVDPV2 and the remaining risk of iVDPV2 in the post-OPV era
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