Pakistan's government and the World Health Organisation (WHO) denied a cover- up and said they had waited until the strain was formally identified. (stock photo)

Pakistan faced a fresh blow to its polio eradication efforts and accusations of a cover-up after officials confirmed an outbreak of a strain thought to have been stamped out.

Seven children have been paralysed in recent months after being infected by a strain of virus thought to have been wiped out, but formerly used in vaccination campaigns.

Officials were accused of trying to hush up the outbreak amid the country's faltering eradication efforts, with a nearly seven-fold jump in cases since 2018.

A source told 'The Guardian' that rather than announce the outbreak, senior officials decided on a secret vaccination campaign to target the strain. Pakistan's government and the World Health Organisation (WHO) denied a cover- up and said they had waited until the strain was formally identified. Britain's Department for International Development, which helps fund polio eradication in Pakistan, said it knew about the cases.

"Absolutely no cover-up," said Zafar Mirza, the Pakistani health minister. "Before we proceeded there was a need for a full genomic sequencing to determine the cause of the virus. The situation is under control."

Global health workers have come close to eradicating the three different types of polio viruses with vaccines containing weakened versions of each strain. Type 2 of the wild virus was declared eradicated worldwide in 2015, and type 3 last month. Yet in rare cases the virus used to create polio drops remains in sewage and mutates to become harmful.

Vaccine-derived outbreaks have been recently seen in Congo, Angola and Nigeria among others.

A WHO spokesman said polio virus type 2 was first detected in August.

Irish Independent