The World Health Organization is sending more than one million polio vaccines to Gaza to be administered over the coming weeks to prevent children being infected after the virus was detected in sewage samples, its chief said on Friday.

“While no cases of polio have been recorded yet, without immediate action, it is just a matter of time before it reaches the thousands of children who have been left unprotected,” Director-General Tedros Adhanom Ghebreyesus said in an opinion piece in Britain’s The Guardian newspaper.

He wrote that children under five were most at risk from the viral disease, and especially infants under two since normal vaccination campaigns have been disrupted by more than nine months of conflict.

Poliomyelitis, which is spread mainly through the fecal-oral route, is a highly infectious virus that can invade the nervous system and cause paralysis. Cases of polio have declined by 99% worldwide since 1988 thanks to mass vaccination campaigns and efforts continue to eradicate it completely.

Israel’s military said on Sunday it would start offering the polio vaccine to soldiers serving in the Gaza Strip after remnants of the virus were found in test samples in the enclave.

Besides polio, the U.N. reported last week a widespread increase in cases of Hepatitis A, dysentery and gastroenteritis as sanitary conditions deteriorate in Gaza, with sewage spilling into the streets near some camps for displaced people.

(Reuters)