GENEVA (AP) -- The World Health Organization has warned countries that a 'dangerous' strain of polio has spread to China from Pakistan.

The U.N. health agency says a genetic link has been confirmed between wild poliovirus type 1 detected in China and a strain circulating in Pakistan.

It says there have been seven confirmed cases involving the WPV1 strain detected in China's Xinjiang province, which borders Pakistan, in the past two months.

WHO spokesman Oliver Rosenbauer says type 1 is more dangerous than type 3 because it is more likely to cause paralysis and spreads more easily. Type 2 polio has been eradicated.

The global health body says countries should strengthen their disease surveillance systems and travellers to Pakistan should be vaccinated against polio.

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