New Delhi, March 10: The World Health Organisation has advised the Centre to test all batches of an oral polio vaccine made by an Indian company after inspections revealed problems with one of its batches, polio control programme officials said.

The officials said that during routine quality tests, a single batch of a monovalent oral polio vaccine (m-OPV1) produced by the company Panacea Biotec was found to have “borderline potency”, raising concerns about its capacity to immunise children against polio.

The m-OPV1 is designed to protect children against wild poliovirus type-1. Panacea has been a major supplier of this vaccine to India’s polio eradication efforts.

The quality problem came to light “recently” during random testing of doses from this specific batch more than six month after the batch was used in Agra in July 2008.

An official said the concern was not about safety, but about its potency — the capacity of the vaccine to elicit the required immune response in children. But sustained immunisation with prior and subsequent doses have protected children in Agra, the official said.

Under quality evaluation protocols, the manufacturer tests every batch produced, the Indian government tests dose samples from 25 per cent to 50 per cent of batches, and the World Health Organisation conducts random sampling of batches, the official said.

A typical batch contains about a million doses of OPV. The official said investigations were now under way to determine how a single batch came to have less than desired potency.

India is among the last four countries in the world still struggling to eradicate polio -- nine years after the first eradication deadline of 2000. Already this year, the government has recorded 17 cases of polio -- 11 in Uttar Pradesh, five in Bihar and one in Delhi.

The other polio-stricken nations are Pakistan, Afghanistan and Nigeria.