Vaccination remains the only effective protection against the disease. (File Photo)Nearly a week after a vaccine-derived polio virus (VDPV) was detected in a sewage sample in Ghaziabad, authorities on Thursday surveyed 5,421 homes having 2,590 children below the age of five, as part of an extensive door-to-door survey covering around 30,000 households in 12 localities.Two of the 12 such localities – Bulandshahr and Shastri Nagar – have been completely surveyed, officials in the Health department said. Besides Bulandshahr and Shastri Nagar, the other areas being surveyed are Raj Nagar, Daulatpura, Panchvati Kot village, Ghukna, Hindon Vihar, Kaila Bhatta, Mirzapur, Vijay Nagar 1, Vijay Nagar 2 and Kharati Nagar, home to around 1.5 lakh people.The virus was detected in a sample collected from the Vijay Nagar sewage pumping station on June 5. Following this, the District Surveillance Unit mapped the sewage drainage network and identified 12 localities falling within the affected area.The survey began on Tuesday and is being closely monitored by the Uttar Pradesh government, the National Centre for Disease Control (NCDC) and the World Health Organization (WHO).Officials said that the detected strain is largely non-virulent and has so far remained contained. “Similar instances have been reported earlier in Varanasi and Meghalaya. Routine sample collection and tests are conducted every fortnight,” an official said.Polio is a highly infectious disease that primarily affects children and can lead to paralysis and, in severe cases, death. Vaccination remains the only effective protection against the disease.India was declared polio-free by the WHO in 2014, making it one of the 11 countries in South East Asia, which have been certified free of wild polio virus.Story continues below this adAccording to the WHO website, apart from routine immunisation, India conducts acute flaccid paralysis surveillance, along with environmental surveillance, which involves regular collection and testing of sewage samples from selected sites from across the country to detect polio virus in faecal matter.According to WHO, VDPVs are extremely rare. In addition to being reported among immunocompromised individuals, VDPVs may also develop in areas with low population immunity, as per WHO.Vaccine derived polio virus originates from oral polio vaccine, which contains a weakened live polio virus. After vaccination, it can briefly replicate in the gut and be excreted in stool.