A two-year-old child from West Garo Hills district in Meghalaya was confirmed to have polio. This is concerning because India was declared polio-free by the World Health Organisation (WHO) in 2014, after the last case was reported in 2011. However, this recent case is not wild polio but vaccine-derived polio, which can occur in people with low immunity. The WHO has been notified, and an investigation is ongoing. WHO doctors have collected samples from the area.
What is Vaccine-Derived Polio?
Polio is a highly infectious disease caused by the poliovirus, which spreads through contaminated water or food, mainly via the faecal-oral route. The virus can be very contagious and may lead to paralysis. Symptoms of polio include fever, headache, fatigue, vomiting, sore throat, neck stiffness, and sensitivity to light, among others.
There are three types of poliovirus: wild poliovirus type 1 (WPV1), wild poliovirus type 2 (WPV2), and wild poliovirus type 3 (WPV3). All three cause similar symptoms. Historically, most polio cases were caused by wild poliovirus.
In 1988, the Global Polio Eradication Initiative was launched to vaccinate people worldwide. While India was declared polio-free in 2014, only two countries, Pakistan and Afghanistan, continue to report cases of wild poliovirus.
Though wild polio cases have decreased significantly, vaccine-derived cases have emerged as a concern.
Types of Polio Vaccines
Two types of polio vaccines are used: Oral Polio Vaccine (OPV) and Inactivated Polio Vaccine (IPV).
OPV: This is the most common polio vaccine in India. It contains a weakened form of the virus and is given as drops. It helps build immunity without causing the disease and is used in mass immunization campaigns.
IPV: This vaccine contains a killed version of the virus and is given by injection. It is part of the routine immunization schedule.
Both vaccines are used in India, though OPV is preferred for ease of administration. However, the weakened virus in OPV can replicate and, in rare cases, cause vaccine-derived polio if it mutates and spreads in areas with low immunity.
According to the US CDC, 524 polio cases in 32 countries in 2023 were linked to vaccine-derived poliovirus.
