Active strain of the polio virus was found in sewage samples in southern India collected last month, officials announced Wednesday.
Around 300,000 children ages three to six in Hyderabad, a city of nearly 7 million, will be vaccinated in the coming week.
India's last case of polio was in 2011, and the country was officially declared polio-free in 2014.
National health officials are calling on residents of Hyderabad to remain calm, maintaining that India is still polio free.
"This is not the first time that a strain has been found but it is a vaccine-derived polio strain that is found com,monly in children with low levels of immunity," CK Mishra, a Health Ministry secretary told reporters.
"They excrete it, which is why it is found in the sewage samples."
State health officials also told residents not to panic, saying that tests to find traces of the polio virus in the environment have been carried out regularly since the country was declared polio free five years ago.
India worked with the World Health Organization, UNICEF, and several volunteer organizations to fight a decades-long battle eradicating the crippling disease.
