What is Vaccine-derived poliovirus?

Introduction: Why this is in the news?

Recent news has highlighted a worrisome development in the fight against polio. According to The Hindu, a reputable newspaper, a report from the Morbidity and Mortality Weekly Report (MMWR) reveals a significant increase in cases of circulating vaccine-derived polioviruses (VDPVs). This surge, a 23% rise from the previous year, amounts to 859 reported cases in the past year alone. What's even more concerning is that these cases have emerged in countries where poliovirus transmission had long been eradicated, including Canada, Israel, the U.K., and the U.S. Moreover, multiple poliovirus types are co-circulating in various countries globally, such as the Democratic Republic of the Congo (DRC), Israel, Malawi, Mozambique, the Republic of the Congo, and Yemen. This unsettling information casts doubt on the attainment of the 2022-2026 Global Polio Eradication Initiative (GPEI) goal of eliminating the last cases of wild poliovirus type 1 (WPV1) and VDPV by this year.

Understanding Vaccine-Derived Poliovirus (VDPV):

Vaccine-derived poliovirus (VDPV) refers to a strain of the poliovirus that has undergone genetic mutations from the weakened, attenuated virus found in the oral polio vaccine (OPV). OPV, administered orally, contains weakened forms of the three types of poliovirus and has been highly effective in reducing global polio cases.

Occurrence and Characteristics of VDPVs:

While rare, there are instances where the weakened virus in the vaccine regains its virulence and disease-causing ability. This can happen when the vaccine virus replicates in the intestines of a vaccinated individual over an extended period. Gradually, genetic changes occur within the virus, leading to its reacquisition of the capability to cause paralysis and other polio-related symptoms.

When a mutated strain of poliovirus emerges due to such circumstances, it is labelled as a vaccine-derived poliovirus. These strains can circulate within communities, resulting in polio outbreaks. It is important to note that VDPVs are generally less virulent and less transmissible than wild-type polioviruses, which are the naturally occurring strains responsible for polio.

Risk Mitigation and Progress:

The risk of VDPVs primarily stems from the use of the oral polio vaccine, which contains live attenuated viruses. In contrast, the inactivated polio vaccine (IPV), administered via injection, does not carry the risk of VDPVs. Consequently, the Global Polio Eradication Initiative has been transitioning from OPV to IPV in recent years. This strategic shift aims to mitigate the occurrence of VDPVs while continuing progress towards the global eradication of polio.

Conclusion:

The emergence of vaccine-derived polioviruses in regions where poliovirus transmission had been eliminated is a cause for alarm. The reported increase in VDPV cases highlights the need for sustained efforts to monitor and combat polio. By transitioning to the inactivated polio vaccine, the global health community strives to minimize the risk of VDPVs while working towards the eradication of polio worldwide.