A two-year-old child from Meghalaya’s West Garo Hills district reportedly tested positive for polio in 2025, a highly contagious and potentially fatal disease that once crippled millions before being nearly wiped out by vaccines. Officials from the Union Health Ministry confirmed that the infection was vaccine-derived, stressing that India’s polio-free status remains unaffected. But what exactly does “vaccine-derived” mean, and is it dangerous? Can such a case spread from one person to another? Let’s break it down.What Is Vaccine-Derived Polio?A vaccine-derived poliovirus (VDPV) is a mutated form of the weakened live virus used in the oral polio vaccine (OPV). According to the Centers for Disease Control and Prevention (CDC), if this weakened strain continues to circulate among communities with poor vaccination coverage or replicates inside a person with a weak immune system, it can revert to a version capable of causing paralysis and illness.Interestingly, the oral polio vaccine (OPV) has played a crucial role in eliminating wild poliovirus globally. It contains one or more weakened strains of the virus and is administered as oral drops, which help build immunity in the gut, stopping the virus from spreading. However, when too few people are vaccinated, the weakened virus can continue moving from person to person, mutating over time, and eventually regaining its disease-causing ability.However, it is important to remember that polio drops are safe and have helped nearly every country eliminate the disease. Still, in extremely rare cases, especially among children with weak immune systems, the vaccine strain can cause infection.Types Of Polio VaccinesThere are two kinds of vaccines used to protect against polio, one given orally and the other through injection.Oral Polio Vaccine (OPV):This is the most widely used vaccine in India. It contains a weakened version of the poliovirus that helps the body build immunity without causing illness. It is administered orally, usually as drops, and is used during mass campaigns such as National Immunization Days.Inactivated Polio Vaccine (IPV):IPV, on the other hand, contains a killed version of the poliovirus and is given as an injection. It forms part of India’s routine immunization schedule and is often delivered in combination with other vaccines.In India, both vaccines are used, though OPV remains preferred because it’s simple to administer during large-scale drives.Vaccine-Derived Polio Cases Detected In IndiaIndia’s last recorded wild poliovirus case occurred years ago, but in 2024, a two-year-old child in Meghalaya was confirmed to have vaccine-derived polio. Officials clarified that this does not affect the country’s polio-free certification, since the virus involved was vaccine-derived rather than wild.Earlier instances have been reported as well. In 2011, a vaccine-derived virus was detected in West Bengal’s Howrah district. Another case emerged in Beed district, Maharashtra, where an 11-month-old boy with an immune disorder developed brain lesions after contracting the vaccine-derived strain and sadly passed away.In 2021, Kerala also documented a rare transmission case: a seven-month-old baby with Severe Combined Immunodeficiency (SCID) received the oral vaccine but couldn’t clear the weakened virus from his system. The virus was later passed to his father through the fecal-oral route, as reported by The Times of India.Why Are Vaccines Triggering Fresh Polio Cases In India?Vaccine-derived polio tends to appear in communities where immunization coverage is low. The weakened virus from OPV can circulate in such areas, undergo genetic changes, and, over time, transform back into a version capable of causing paralysis, the World Health Organization (WHO) explains. When this mutated strain starts spreading in the community, it’s known as a “circulating vaccine-derived poliovirus” (cVDPV).In India, the few vaccine-derived cases reported so far have primarily been seen in children with weak immune systems, who are unable to fight off even the weakened vaccine virus. Poor sanitation and incomplete vaccination coverage further increase the risk of such mutations.Can Vaccine-Derived Polio Be Prevented?The oral polio vaccine remains highly effective at preventing the spread of the virus from person to person, and it is easy, drop-based delivery has made it the foundation of the global eradication effort. However, one drawback is that, on rare occasions, it can cause infection or transmit the weakened virus to others, as noted by the CDC.To reduce this risk, many experts advocate switching entirely to the inactivated polio vaccine (IPV). Yet IPV has its own challenges: it requires trained medical staff for injection, which could lower immunization rates, and unlike OPV, it does not stop virus transmission through the gut.Countries such as the United States and Canada have already moved entirely to IPV. India, however, continues to use both forms, IPV as part of routine childhood immunization and OPV for children under five during Pulse Polio campaigns.Polio vaccination remains the best protection against both wild and vaccine-derived strains. Maintaining high IPV coverage is essential to keeping India and the rest of the world polio-free, ensuring that even rare mutations never regain a foothold.
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