What is Vaccine-Derived Poliovirus (VDPV)?
Vaccine-Derived Poliovirus (VDPV) refers to a strain of the poliovirus that has genetically mutated from the original strain contained in the Oral Polio Vaccine (OPV). While the OPV is highly effective in preventing polio, in rare instances, the weakened virus in the vaccine can mutate and regain its ability to cause disease, especially in under-immunized communities.
How Does VDPV Occur?
When a child is vaccinated with OPV, the weakened virus replicates in the intestine and is excreted in the feces. In areas with poor sanitation, this virus can spread to others through contaminated water or food. If the vaccine-derived virus circulates long enough, it can mutate and revert to a form capable of causing paralysis, leading to Vaccine-Derived Poliovirus.
Types of VDPV
There are three types of VDPVs:1. Circulating Vaccine-Derived Poliovirus (cVDPV): This occurs when the weakened virus from the OPV circulates in the community and undergoes genetic changes.
2. Immunodeficiency-Related Vaccine-Derived Poliovirus (iVDPV): This occurs in individuals with primary immunodeficiency disorders who cannot clear the virus, allowing it to mutate.
3. Ambiguous Vaccine-Derived Poliovirus (aVDPV): This is a VDPV detected in individuals with no clear source.
Risk Factors for VDPV
The primary risk factor for VDPV is low immunization coverage. When a large proportion of a population is not immunized, the weakened virus in the OPV can circulate and mutate. Poor sanitation and hygiene practices also contribute to the spread of the virus.Prevention of VDPV
The key to preventing VDPV is maintaining high immunization coverage with polio vaccines. Both the OPV and the Inactivated Polio Vaccine (IPV) are crucial in the fight against polio. IPV, which contains a killed virus, does not carry the risk of VDPV and is recommended for use in combination with OPV in many immunization programs.Global Efforts and Strategies
The Global Polio Eradication Initiative (GPEI) has been working tirelessly to combat both wild poliovirus and VDPV. Strategies include:- Switching from trivalent OPV to bivalent OPV: This reduces the risk of VDPV by removing the type 2 component, which is more likely to revert to a virulent form.
- Introducing IPV: IPV is being introduced worldwide to provide immunity without the risk of VDPV.
- Improving Sanitation and Hygiene: Enhancing sanitation and hygiene practices helps reduce the spread of all polioviruses.
Detection and Response
Surveillance for poliovirus, including VDPV, is critical. This involves monitoring cases of acute flaccid paralysis (AFP) and testing environmental samples. Rapid response teams are deployed to areas with detected cases of VDPV to conduct immunization campaigns and prevent further spread.Conclusion
While Vaccine-Derived Poliovirus represents a challenge in the fight against polio, it is a manageable one. Continued efforts to maintain high immunization coverage, improve sanitation, and use both OPV and IPV strategically are essential to mitigating the risks and ultimately achieving a polio-free world. Active surveillance and rapid response are also key components in controlling outbreaks of VDPV.
