UNDERSTANDING VACCINE-DERIVED POLIO AND ITS IMPLICATIONS

Why in the News?

A recent case of vaccine-derived polio (VDPV) has been reported in a two-year-old child from Tikrikilla, Meghalaya, marking the first known case of its kind in the region. While India has successfully eradicated wild polio, the emergence of VDPV raises concerns about vaccine strategies and public health measures.

Source : Hindu
What is Vaccine-Derived Polio?

Definition:

  • Vaccine-derived polio is a rare condition that occurs when the weakened (attenuated) strain of poliovirus used in the Oral Polio Vaccine (OPV) mutates and regains the ability to cause paralysis. This can happen in areas with low vaccination coverage, poor sanitation, or among immunocompromised individuals.

Mechanism:

  • The OPV contains a live, attenuated virus designed to trigger an immune response without causing the disease. After administration, the attenuated virus replicates in the intestines for a limited period and is excreted in the stool. In rare cases, the virus can mutate and regain neurovirulence, potentially causing disease and spreading to others. This mutated virus is referred to as circulating vaccine-derived poliovirus (cVDPV) when it is detected in multiple sources over time, indicating community transmission.

Types of Poliovirus and Vaccines:

  • Wild Poliovirus (WPV): There are three types of wild poliovirus: WPV1, WPV2, and WPV3. WPV2 was declared eradicated in 2015, and WPV3 in 2019. WPV1 remains endemic in some countries.
  • Inactivated Polio Vaccine (IPV): Developed by Jonas Salk, IPV contains an inactivated virus and provides systemic immunity. It does not pose a risk of causing vaccine-associated paralytic poliomyelitis (VAPP) but is less potent compared to OPV.
  • Oral Polio Vaccine (OPV): Developed by Albert Sabin, OPV contains a live, attenuated virus and is administered orally. It is more effective in providing intestinal immunity and interrupting virus transmission but carries a small risk of reverting to a virulent form.

Implications of Vaccine-Derived Polio

Public Health Challenges:

  • The occurrence of VDPV highlights challenges in immunization coverage and public health infrastructure. Regions with low vaccination rates are more susceptible to VDPV outbreaks. Ensuring high immunization coverage and maintaining robust surveillance systems are crucial to prevent the spread of both wild and vaccine-derived polio.

Vaccine Strategy Adjustments:

  • The rise in VDPV cases, especially those related to type 2 poliovirus, led to a global switch from trivalent OPV (containing all three types) to bivalent OPV (types 1 and 3) in 2016. Despite this switch, VDPV cases have increased, indicating the need for further strategic adjustments. The introduction of genetically modified novel OPV type 2, which is less likely to revert to neurovirulence, represents a critical step in addressing VDPV outbreaks.

Balancing Risks and Benefits:

  • OPV has been instrumental in reducing polio cases globally due to its effectiveness in preventing virus transmission. However, the risk of VDPV requires careful consideration. Balancing the use of OPV and IPV, based on local epidemiological data and risk assessments, is essential for effective polio eradication strategies.

Measures to Prevent and Control Vaccine-Derived Polio

Enhanced Immunization Coverage:

  • Achieving and maintaining high immunization coverage is critical to preventing VDPV. Public health initiatives must focus on reaching every child, especially in hard-to-reach and underserved areas, to ensure complete immunization. Regular immunization campaigns and community engagement are vital for this purpose.

Improved Surveillance Systems:

  • Robust surveillance systems are needed to detect VDPV cases early and respond swiftly. Monitoring acute flaccid paralysis (AFP) cases and conducting environmental surveillance for poliovirus are essential components of a comprehensive surveillance strategy. Rapid response teams should be ready to investigate and contain outbreaks.

Sanitation and Hygiene Improvements:

  • Poor sanitation and hygiene are significant factors contributing to the spread of poliovirus, including VDPV. Efforts to improve water quality, sanitation facilities, and hygiene practices can reduce transmission risks. Public health education on sanitation and hygiene is crucial for preventing not only polio but other infectious diseases as well.

Research and Development:

  • Continued research into safer and more effective polio vaccines is necessary. The development of the novel OPV type 2 under the WHO’s Emergency Use Listing is an example of innovation in response to VDPV challenges. Ongoing research and adaptation of vaccine strategies will be key to achieving and sustaining polio eradication.

Conclusion

The case of vaccine-derived polio in Meghalaya underscores the need for vigilance and adaptability in public health strategies. understanding vaccine-derived polio provides insights into the complexities of immunization programs, the importance of public health infrastructure, and the challenges of disease eradication. As India moves forward in its fight against polio, the lessons learned from managing VDPV will be crucial in shaping future public health policies and ensuring the health and safety of all citizens.