Vaccine-Derived Polio Detected

Context

Vaccine-derived polio (VDPV) is an infrequent, though potentially alarming medical issue, which stems from the administration of oral polio vaccines (OPV). This is a circumstance that may happen when the reduced virulence, in OPV, changes its genetic makeup and it once again becomes pathogenic for paralysis.

What is Vaccine-Derived Polio?

Vaccine-derived polio is a condition by which the OPV strain of poliovirus adapted for the vaccine gets mutated, reverts to pathogenicity and causes paralysis. The OPV has a live and weakened virus which once ingested will stimulate the immune system of an individual in case of exposure to actual polio causing virus. But in certain circumstances, this weakened virus may undergo a process of virulent reversion during its replication in the intestines and result in VDPV.

Polio Vaccines and Their Role in VDPV

• Oral Polio Vaccine (OPV): OPV is a trivalent live attenuated vaccine and the mainstay of global poliomyelitis eradination program. But with that capability it offers VDPV Although everything comes in twos, the twosome is not desirable. So, it multiplies in the intestinal tract and thereby provides immunity but if it gets circulated amongst a partly immunized population or in a locality having poor sanitation, it may turn virulent.
• Inactivated Poliovirus Vaccine (IPV): The other poliomyelitis vaccine is the inactivated poliovirus vaccine and does not contain live virus hence does not pose the risk of VDPV. Salk created IPV in the 1950s and it involved injections whereas there is no possibility of becoming something worse. Although it is more effective in producing immunity than OPV, it is slightly costly and technically complex to administer compared with OPV; it is incapable of being administered in mass immunization campaigns in developing countries.

Prevention Strategies

Immunization Campaigns: 

1. Universal Immunization: Since VDPV is a strain of poliovirus, the immunisation coverage plays a vital role in controlling VDPV. This includes the annual vaccination sessions and also sustained excellent EPI service delivery in the country.
2. Switch to Bivalent OPV: Replacement of trivalent with bivalent OPV in 2016 was to supplement efforts aimed at eradicating type 2 WPV and reducing type 2 cVDPV. This has led to more type 2 VDPV outbreaks requiring adjustments of the previous strategies outlined hence more changes.

Novel Oral Polio Vaccines: As a result of the problems presented by traditional OPV, the WHO has granted an Emergency Use Listing for a genetically altered type 2 nOPV2. This vaccine was deployed to the field in March 2021 and WHO prequalified in December 2023; it is much less likely to revert to neurovirulence, which minimizes the risk of VDPV.

Public Health Measures

• Surveillance: Increase in surveillance of AFP is important in the early detection of VDPV.
• Sanitation and Hygiene: Hence, there is a need to review sanitation and hygiene practices since infection with VDPV can occur in the regions where the virus may be circulating.
• Community Awareness: The other important aspect within consideration in managing VDPV is to ensure that members of the affected communities or potentially at risk are educated on the risks and preventions to the virus.

Addressing Challenges

• Low Immunization Coverage: It is important to note that low levels of immunization coverage increase the vulnerability of VDPV of occurrence. Education and enhancing participation of people is important in relation to these gaps, enforcing targeted vaccination, and increasing the ability to obtain healthcare services.
• Immunocompromised Individuals: Patients with other related immunodeficiency diseases or diseases that affect their immune system are more susceptible to VDPV. It is therefore a requisite that these individuals receive IPV which is non – infective.
• Economic and Logistical Challenges: The switch from OPV to IPV or novel vaccines including nOPV2 is associated with some costs and difficulties relating to the process. Some of the barriers include higher costs that are even prohibitive in resource-poor environments and the cold chain that is challenging to maintain in a limited-resource environment.

Conclusion

Vaccine-derived polio is a complex issue that requires a multifaceted approach for prevention. While OPV has been instrumental in reducing polio cases globally, the risk of VDPV necessitates the development and use of safer vaccines like nOPV2. Enhancing immunization coverage, improving sanitation and hygiene, and maintaining robust surveillance are critical components of a comprehensive strategy to prevent VDPV. As public health efforts continue to evolve, addressing the challenges associated with VDPV will be essential for achieving and sustaining polio eradication.

Source: The Hindu