Polio is a devastating disease that has been eradicated in most parts of the world through extensive immunization efforts. However, recent findings by the World Health Organization (WHO) have raised concerns about the potential resurgence of this debilitating virus in India.
Investigation into Polio Contamination in India
The Ministry of Health and Family Welfare in India has launched an investigation following the detection of type-2 polio virus contamination in vaccination vials used in Uttar Pradesh, Maharashtra, and Telangana. The WHO found the virus in sewage and stool samples during routine surveillance; however, these cases have not developed into poliomyelitis, also known as polio.
The Indian government has ordered additional immunisation in these three states, even though the detected virus traces are attenuated, meaning they’ve been weakened and do not cause paralysis. Individuals who receive the contaminated vaccine usually excrete the virus through feces for 4-6 weeks before it eventually dies off.
The History and Eradication of Type-2 Polio in India
India was declared polio-free in 2014, with the last reported case being in January 2011. The use of trivalent vaccine (tOPV) that contained type-2 poliovirus was phased out globally and in India in April 2016 under the Polio End Game strategy. This recent detection indicates the usage of a vaccine containing type-2 poliovirus, even after its discontinuation. The last known case of wild type-2 polio globally was reported in 1999 from Aligarh, India.
To further minimize the risk of type-2 vaccine-derived poliovirus outbreaks, India switched to a bivalent vaccine (bOPV) from tOPV, which certified the global eradication of wild type-2 polio.
Risks Associated with Oral Polio Vaccines
Oral polio vaccines (OPV) contain a weakened but live poliovirus, which can cause paralytic polio. The vaccine virus can be expelled by immunized children and potentially spread to others. This allows the virus to mutate into a more potent form, leading to the emergence of Vaccine-Derived Poliovirus (VDPV). Outbreaks of VDPV can occur in populations with low immunization levels, much like imported wild polio.
The WHO’s Polio Eradication and Endgame Strategic Plan has called for the phased removal of OPVs by 2019. Therefore, replacing OPV with Inactivated Polio Vaccine (IPV) is critical for eradicating polio.
Challenges of Using IPV Over OPV
While IPV does not carry the risk of causing polio, it has its own set of challenges. IPV induces very low levels of immunity in the intestines, meaning that if a person immunized with IPV is infected with wild poliovirus, the virus can proliferate in the intestines and be shed in the feces, risking further circulation.
Furthermore, IPV is over five times more expensive than OPV and requires trained health workers for administration along with sterile injection equipment and procedures.
India’s Efforts to Prevent Polio Outbreak
To combat potential outbreaks, India launched the Pulse Polio program in 2018 to administer OPVs to over 17 crore children under the age of five on National Immunisation Day on January 28.
About Polio
Polio is a highly contagious disease caused by a virus that invades the nervous system and can cause paralysis. The virus is transmitted person-to-person, predominantly through the fecal-oral route or through contaminated food or water. Initial symptoms include fever, fatigue, headache, vomiting, neck stiffness, and limb pain. In severe cases, polio can cause permanent paralysis. There is no cure for polio, and prevention through immunization is the only protection.
