NEW DELHI: At least three batches of polio vaccines containing 1.5 lakh vials have been found contaminated with type 2 polio virus, putting at risk India’s “polio free” status as children born after April 2016 — when the type 2 virus was withdrawn worldwide including in India — do not have immunity to this particular virus, sources said.

The health ministry and the World Health Organisation (WHO) have stepped up surveillance, particularly in

, Maharashtra and

where the contaminated vaccines were administered to children.

were manufactured by Ghaziabad-based firm Biomed, as reported by TOI in its September 29 edition.

“The contamination can have very serious ramifications on public health because it is tantamount to reintroducing into the community a virus that had been eradicated. The WHO and health authorities are keeping a close watch for any active strain of the virus in stool samples or in sewage,” a senior official said.

The ministry has set up a three-member committee to probe how the eradicated virus got introduced again even after orders for its destruction from the manufacturing and supply chain. The panel has been asked to submit its report within a week.

While the Biomed managing director was arrested on Thursday, four of its directors are absconding, the official said. The Drugs Controller General of India has filed an FIR and issued a showcause notice to the company asking it to stop manufacturing till further orders.

According to experts, all oral polio vaccines (OPV) contain live polio viruses that are shed by vaccinated children in their stool. Now, the government, regulatory authorities and medical practitioners are worried that if type 2 virus passes into the sewage or water system, it may regain neuro-virulence and spread polio.

“Another major risk is of virus mutation, which is a common phenomenon in 3 to 6 months,” the official said.

Earlier, trivalent polio vaccines containing type 1, 2 and 3 were in use but after the type 2 polio virus was eradicated worldwide, governments switched to bivalent vaccines, containing only type 1 and type 3 viruses. In 2016, India, in line with WHO guidance, had ordered withdrawal and destruction of all trivalent OPV stocks by April 2016.

Biomed supplied polio vaccines for the government’s universal immunisation programme. The contamination was first suspected when surveillance reports from UP showed signs of the virus in stool samples of some children. Following these reports, samples of OPV vaccines were lifted by drug inspectors and sent for testing to the Central Drug Laboratory in Kasauli, which confirmed the contamination.

Though the government has ordered immunisation of children with additional doses in the three states, it is difficult to identify those children quickly, the official said.

In March 2014, India was officially declared “polio free” by the WHO. The last case of wild polio virus type 2 in the country was in 1999. However, India continues to maintain a highly sensitive surveillance system for polio. All cases of paralysis with sudden onset in children up to 15 years (which is called Acute Flaccid Paralysis or AFP) are picked up by the polio surveillance network. Each of these cases is followed up and stool samples tested for polio virus in WHO accredited laboratories. In addition, sewage samples are collected from over 30 sites across the country for polio virus detection at regular intervals.