What is Vaccine-Derived Poliovirus?
Vaccine-derived poliovirus (VDPV) is a strain of the poliovirus that has genetically mutated from the strain contained in the oral polio vaccine (OPV). While the OPV is highly effective in providing immunity against
polio, in rare instances, the weakened virus used in the vaccine can mutate and regain its ability to cause disease. This occurs under conditions where immunization coverage is low, allowing the virus to circulate in a community and undergo genetic changes.
How Does Vaccine-Derived Poliovirus Occur?
VDPV occurs when the live attenuated virus in the OPV is excreted by vaccinated individuals. If the virus is allowed to circulate in an under-immunized population, it can continue to replicate and mutate over time. If these mutations allow the virus to regain neurovirulence, it can cause outbreaks similar to those caused by the wild poliovirus. This phenomenon underscores the importance of maintaining high levels of
vaccination coverage in communities.
What are the Types of Vaccine-Derived Poliovirus?
There are three main types of VDPVs:
Circulating VDPV (cVDPV): This occurs when there is sustained person-to-person transmission of the vaccine-derived virus in a community.
Immunodeficiency-related VDPV (iVDPV): This type occurs in individuals with immune system disorders who cannot clear the vaccine virus, allowing it to mutate over prolonged periods.
Ambiguous VDPV (aVDPV): These are isolated cases where the origin of the virus is not clearly linked to either of the above categories.
Why is Vaccine-Derived Poliovirus a Concern?
The emergence of VDPVs is a concern because they can lead to outbreaks of paralytic polio in under-immunized areas. While the risk is low compared to the benefits of the OPV, it highlights the complex balance between
public health safety and the goal of eradicating polio. It underscores the need for strong immunization systems and surveillance to detect and respond to any polio outbreak, whether from wild or vaccine-derived strains.
How Can Vaccine-Derived Poliovirus be Prevented?
Preventing VDPVs involves several strategies:
Maintaining High Immunization Coverage: Ensuring that a high percentage of the population is vaccinated can prevent the circulation and mutation of the vaccine virus.
Switching to Inactivated Polio Vaccine (IPV): IPV does not contain live virus, eliminating the risk of vaccine-derived strains. Many countries have transitioned to using IPV as part of their immunization schedules.
Monitoring and Surveillance: Active surveillance systems help detect VDPVs early, allowing for rapid response and containment measures.
What is the Global Response to VDPV?
The global response to VDPV involves coordinated efforts by organizations like the
World Health Organization (WHO) and the
Global Polio Eradication Initiative (GPEI). These organizations work with countries to strengthen immunization programs, transition to IPV, and enhance surveillance. In regions where cVDPV outbreaks occur, targeted vaccination campaigns are conducted to stop transmission and protect at-risk populations.
Conclusion
Vaccine-derived poliovirus presents a unique challenge in the fight against polio. While the occurrence of VDPVs is rare, it highlights the need for continued vigilance in immunization efforts and global health security measures. The transition to IPV and the strengthening of health systems are critical steps in ensuring that the gains made against polio are sustained, ultimately leading to the
eradication of polio worldwide.
