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Rare case of vaccine-derived polio in Meghalaya
Context
A case of vaccine-derived polio (VDPV) has been confirmed in a two-year-old child from West Garo district, Meghalaya. Although polio was declared eradicated in India in 2011, the emergence of vaccine-derived polio in an immuno-deficient child (iVDPV) has raised concerns about the continued use of the oral polio vaccine (OPV).
What is Vaccine-Derived Polio?
- Poliomyelitis, or polio, is a highly infectious viral disease that can lead to paralysis and even death.
- It is caused by the poliovirus, which exists in three types: wild poliovirus type 1 (WPV1), type 2 (WPV2), and type 3 (WPV3).
- India’s success in eradicating WPV1 and WPV3 is notable, but the presence of vaccine-derived poliovirus (VDPV) indicates ongoing risks.
- VDPV arises from the oral polio vaccine (OPV), which contains a weakened form of the poliovirus.
- While OPV has been crucial in reducing global polio cases, it carries a rare risk of causing vaccine-associated paralytic poliomyelitis (VAPP) in approximately 1 in 2.7 million doses.
- In immuno-deficient individuals, the weakened virus can persist and mutate into a form that may cause polio, known as
- The recent case in Meghalaya is classified as iVDPV, a form of polio that occurs in individuals with primary immunodeficiency (PID), who cannot effectively clear the virus from their systems.
OPV vs IPV:
- Oral Polio Vaccine (OPV): Administered orally, OPV induces immune responses in both the blood and the intestines. This dual immunity helps prevent the virus from spreading in communities with high vaccination coverage. However, in areas with low vaccination rates, the vaccine-derived virus can continue to circulate, mutate, and potentially cause polio.
- Inactivated Polio Vaccine (IPV): IPV, given via injection, contains inactivated poliovirus that cannot replicate. It generates a strong immune response in the blood, preventing paralysis. However, it is less effective at inducing immunity in the intestines, meaning individuals can still carry and potentially transmit the wild poliovirus.
- The switch to IPV, which has been introduced in India since 2017, aims to mitigate the risks associated with OPV. IPV’s inability to cause VAPP or iVDPV makes it a safer alternative, though it may require higher coverage to achieve similar community immunity.
Fact Box: About Poliomyelitis (Polio)
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