Vaccine-Derived Polio
Description
Vaccine-Derived Polio
Description:
Polio has been nearly eradicated worldwide thanks to vaccination efforts, but vaccine-derived poliovirus (VDPV) poses a unique challenge in the final stages of eradication. This comprehensive article explores what vaccine-derived polio is, how it emerges, its global impact, and the strategies in place to manage and prevent outbreaks. It delves into the types of VDPVs, the role of the oral polio vaccine, and the global transition to the inactivated polio vaccine. By understanding these complexities, we can better appreciate the ongoing efforts to achieve a polio-free world.
Why in News?
A polio case has been confirmed in a two-year-old child in Meghalaya, raising concerns as India was declared polio-free by WHO in 2014. The infection is vaccine-derived.
The cases of polio that have been seen historically have generally been of wild poliovirus. In 1988, the Global Polio Eradication Initiative was launched for equitable vaccine administration. While India was declared polio-free in 2014, only 12 cases of paralysis caused by wild poliovirus were reported from just two countries: Pakistan and Afghanistan.
However, while the number of wild poliovirus cases decreased, there was another type of polio cases that increased: vaccine-derived.
Hereby, discussing Vaccine derived Polio, its causes, implications, and the steps required to prevent its spread.
What is Vaccine-Derived Polio (VDPV)?
Vaccine-derived polio occurs when the weakened poliovirus, present in the oral polio vaccine (OPV), mutates over time and regains its ability to cause paralysis. This typically happens in communities with low immunization rates, where the virus can circulate for extended periods. While the OPV is safe and effective, under-immunized populations allow the virus to survive and eventually mutate, leading to VDPV outbreaks.
Types of Vaccine-Derived Polioviruses
VDPVs are categorized based on how they behave and the context in which they are found:
· Circulating VDPV (cVDPV): This type of VDPV occurs when the mutated virus spreads within communities, causing outbreaks. cVDPVs are of particular concern in areas with low vaccination coverage.
· Immunodeficiency-related VDPV (iVDPV): Individuals with primary immunodeficiencies can sometimes harbor the vaccine virus for extended periods, during which it can mutate into iVDPV. These individuals may excrete the virus for years, posing a risk to others.
· Ambiguous VDPV (aVDPV): These cases are less common and occur when a VDPV strain is detected, but its source is unclear. These instances are often identified through environmental surveillance.
How Does Vaccine-Derived Polio Spread?
VDPV spreads in much the same way as the wild poliovirus, primarily through the fecal-oral route. In areas with poor sanitation, the virus can contaminate water supplies, leading to community spread. The risk of VDPV transmission is particularly high in areas where vaccination rates are low, as the virus can circulate more easily among under-immunized populations.
Causes of Vaccine-Derived Polio
1. Low Immunization Coverage: The primary cause of vaccine-derived polio is inadequate vaccination coverage. In communities where a significant portion of the population is unvaccinated, the weakened virus from the OPV can continue to spread and mutate.
2. Prolonged Circulation: In areas with poor sanitation and hygiene, the poliovirus can circulate for longer periods, increasing the risk of mutation.
3. Genetic Changes in the Virus: Over time, the poliovirus in the OPV can undergo genetic changes, which may restore its virulence, leading to VDPV.
The Difference Between Wild Polio and Vaccine-Derived Polio
It is crucial to understand the distinction between wild polio and vaccine-derived polio. While wild poliovirus occurs naturally, vaccine-derived polio is a byproduct of the immunization process itself. Despite this, the symptoms and consequences of both types of polio are identical, emphasizing the need for robust vaccination programs.
Prevention and Control of Vaccine-Derived Polio
1. Strengthening Immunization Programs: Ensuring that every child receives the full course of polio vaccines is the most effective way to prevent vaccine-derived polio. High vaccination coverage stops the virus from spreading and mutating.
2. Switching to Inactivated Polio Vaccine (IPV): Some countries have transitioned from OPV to Inactivated Polio Vaccine (IPV), which contains a killed virus that cannot cause VDPV. This switch is a critical step in the global polio eradication strategy.
3. Monitoring and Surveillance: Active surveillance for poliovirus, including environmental sampling, helps detect the presence of VDPV early, allowing for rapid response measures.
4. Public Awareness: Educating communities about the importance of vaccination and the risks associated with low immunization rates can help in preventing outbreaks of vaccine-derived polio.
Global Response to Vaccine-Derived Polio
The World Health Organization (WHO) and other international bodies are actively working to combat vaccine-derived polio. Efforts include the development of new vaccines, such as the novel oral polio vaccine (nOPV), designed to reduce the risk of VDPV. Global initiatives aim to strengthen immunization systems and enhance the capacity for rapid outbreak response.
Conclusion
Vaccine-derived polio presents a unique challenge in the fight against polio. While it is a rare phenomenon, its occurrence underscores the importance of maintaining high immunization coverage and strengthening public health infrastructure.
