The recent polio outbreak in Syria has originated from Pakistan, according to the World Health Organisation (WHO). The WHO’s Disease Outbreak News on Monday said 13 cases of wild poliovirus type 1 (WPV1) have been confirmed in the Syrian Arab Republic.

Genetic sequencing indicates that the isolated viruses are most closely linked to virus detected in environmental samples in Egypt in December 2012, which in turn had been linked to wild poliovirus circulating in Pakistan. Closely related wild poliovirus strains have also been detected in environmental samples in Israel, West Bank and Gaza Strip since February 2013. Wild poliovirus had not been detected in the Syrian Arab Republic since 1999, the WHO said.

Before this, the polio virus from Pakistan was already found in Egypt, Palestine and Israel. While children were infected by the virus, since there was some system of immunisation there, they were not paralysed unlike in Syria, which did enjoy 14 years of polio-free status. Pakistan was responsible for the international spread in 2011 and the virus from Pakistan caused an outbreak in western China, according to the WHO.

A comprehensive outbreak response continues to be implemented across the region. On October 24, an already-planned large-scale supplementary immunisation activity was launched in the Syrian Arab Republic to vaccinate 1.6 million children against polio, measles, mumps and rubella, in both government-controlled and contested areas, the Disease Outbreak News said.

Given the current situation in Syria, frequent population movements across the region and the immunisation level in key areas, the risk of further international spread of wild poliovirus type 1 across the region is considered to be high. A surveillance alert has been issued for the region to actively search for additional potential cases.