What are Vaccine-Derived Polioviruses (VDPV)?
Vaccine-Derived Polioviruses (VDPVs) are strains of the poliovirus that have genetically mutated from the strain contained in the oral poliovirus vaccine (OPV). While the OPV is highly effective in immunizing individuals and eradicating polio, under rare circumstances, the attenuated virus used in the vaccine can change over time and behave more like the wild poliovirus. These mutated strains are known as VDPVs and can cause outbreaks in populations with low immunization coverage.
How do VDPVs occur?
VDPVs occur when the weakened virus in the OPV passes through the intestinal tract of vaccinated individuals and is excreted into the environment. If the virus continues to circulate in under-immunized communities, it can undergo genetic changes and regain neurovirulence. This situation is particularly concerning in areas with poor sanitation and low vaccination rates, where the mutated virus can spread more easily.
Types of VDPVs
There are three main types of VDPVs: cVDPV (Circulating Vaccine-Derived Poliovirus): This type occurs when the mutated virus spreads in the community, causing outbreaks. It is the most significant public health concern among the VDPVs.
iVDPV (Immunodeficiency-Related Vaccine-Derived Poliovirus): Occurs in individuals with primary immunodeficiency disorders who are unable to clear the vaccine virus from their bodies, leading to prolonged virus shedding.
aVDPV (Ambiguous Vaccine-Derived Poliovirus): This category includes VDPVs that cannot be classified in the other two categories, often due to insufficient epidemiological information.
Why are VDPVs a concern?
VDPVs are a concern because they can cause outbreaks of poliomyelitis in under-immunized populations, mimicking the behavior of wild poliovirus. This challenges the global polio eradication efforts, particularly in regions with poor healthcare infrastructure. The emergence of VDPVs underscores the importance of maintaining high vaccination coverage to prevent the virus from circulating and mutating.
How are VDPVs detected?
VDPVs are detected through
surveillance systems that monitor for cases of acute flaccid paralysis (AFP) and environmental surveillance that tests sewage samples. Genetic sequencing is used to differentiate between wild poliovirus, Sabin-like virus (vaccine strain), and VDPVs. This allows health authorities to identify and respond to VDPV outbreaks promptly.
Increase Immunization Coverage: Ensuring high vaccination coverage in all communities to prevent the circulation of VDPVs.
Switch to Inactivated Poliovirus Vaccine (IPV): Transitioning from OPV to
IPV, which contains inactivated virus and does not carry the risk of VDPV formation.
Outbreak Response: Rapid response to VDPV outbreaks, including mass vaccination campaigns and enhanced surveillance.
Sanitation Improvements: Improving sanitation and hygiene to reduce the spread of poliovirus in the environment.
Future of Polio Eradication and VDPVs
The global polio eradication initiative aims to eliminate all types of poliovirus, including VDPVs. The ultimate goal is to switch entirely to IPV, which will eliminate the risk of VDPV formation. Continued vigilance through robust surveillance and maintaining high immunization coverage are crucial to achieving and sustaining a polio-free world. In summary, VDPVs represent a rare but significant challenge in the context of polio eradication. Understanding the mechanisms of VDPV emergence, maintaining high vaccination rates, and promptly responding to outbreaks are essential strategies to control and eventually eradicate poliovirus globally.
