What is Vaccine-Derived Poliovirus (VDPV)?
Vaccine-derived poliovirus (VDPV) refers to strains of the poliovirus that have genetically mutated from the strain contained in the oral polio vaccine (OPV). While OPV is highly effective in immunizing populations against
poliovirus and has been crucial in reducing global polio cases, in rare instances, the weakened virus used in the vaccine can mutate and revert to a form capable of causing disease, particularly in areas with low vaccination coverage.
How Does VDPV Occur?
VDPV occurs when the attenuated (weakened) virus in the
oral polio vaccine circulates in under-immunized populations. Over time, genetic changes can occur, leading the virus to regain its ability to cause paralysis. This phenomenon is more likely to occur in communities where immunization rates are low, allowing the mutated virus to spread from person to person.
What are the Types of VDPV?
There are three main types of VDPV: Circulating VDPV (cVDPV): These occur when the vaccine-derived virus is transmitted among individuals in communities over a prolonged period, especially in areas with poor sanitation and low vaccination rates.
Immunodeficiency-related VDPV (iVDPV): These occur in people with primary immunodeficiency disorders who are unable to clear the virus from their bodies, allowing it to mutate.
Ambiguous VDPV (aVDPV): These are isolated cases where the origin of the VDPV is unclear, and they do not fit into the categories of circulating or immunodeficiency-related VDPVs.
How is VDPV Detected?
VDPV is detected through
surveillance systems that involve monitoring for cases of acute flaccid paralysis (AFP) and environmental sampling, such as testing sewage for the presence of poliovirus. Genetic sequencing is used to determine whether the virus is a wild strain or a vaccine-derived strain and to track its evolution.
What are the Public Health Implications of VDPV?
The emergence of VDPVs poses a significant challenge to polio eradication efforts. While wild poliovirus cases have drastically declined, cVDPV outbreaks can occur in areas with low immunization rates, threatening to reverse progress. Therefore, maintaining high vaccination coverage and robust surveillance systems is crucial to preventing outbreaks.How Can VDPV Outbreaks be Prevented?
Prevention of VDPV outbreaks involves several key strategies: Maintaining high immunization coverage to ensure community immunity and prevent the spread of both wild and vaccine-derived poliovirus.
Switching from OPV to inactivated polio vaccine (
IPV), which contains no live virus and therefore cannot mutate.
Implementing strong surveillance systems to quickly identify and respond to any cases of polio, whether caused by wild virus or VDPV.
Ensuring access to clean water and improved sanitation to reduce the spread of all types of poliovirus.
What is the Role of the Global Polio Eradication Initiative (GPEI) in Addressing VDPVs?
The
Global Polio Eradication Initiative (GPEI) plays a critical role in combating VDPVs by supporting vaccination campaigns, enhancing surveillance, and coordinating international responses to outbreaks. GPEI also supports the transition to IPV, which is a key step in eliminating the risk of VDPVs entirely.
What Challenges Remain in Eliminating VDPV?
Challenges in eliminating VDPV include maintaining high vaccination rates in conflict zones and remote areas, addressing public misconceptions about vaccines, and ensuring sufficient funding and political will to sustain eradication efforts. Additionally, transitioning entirely to IPV requires overcoming logistical and financial barriers in low-resource settings.Conclusion
Vaccine-derived poliovirus poses a unique challenge in the quest to eradicate polio. While the risk of VDPV is low compared to the benefits of vaccination, it underscores the importance of maintaining high immunization coverage and strong surveillance systems. Continued global efforts and collaboration are essential to addressing the challenges posed by VDPVs and achieving a polio-free world.
