A strain of polio virus from Pakistan has been isolated in neighboring China and there is a high risk of further international spread due to upcoming Muslim pilgrimage to Mecca, the World Health Organization said Tuesday.

The WHO says nine cases have been confirmed in China so far, according Reuters.

Pakistan is currently being affected by nationwide transmission of Wild poliovirus type 1. The country had reported 384 cases so far in 2011 compared to 48 cases in the same period last year.

The report of the spreading virus comes as the WHO noted in a released statement that efforts to vaccinate children in Pakistan have been inadequate due to security problems.

More than 200,000 children have been regularly missed during supplemental immunization activities over the past two years in the Western part of Pakistan known as the Federally Administered Tribal Areas. The area also includes the region known as the Khyber agency.

The WHO rates as “high” the risk of further international spread from Pakistan, given that large-scale movements associated with pilgrimages to Mecca, Saudi Arabia in the coming months.