JERUSALEM (AP) — The U.N. health agency and partners are launching a campaign starting Sunday to vaccinate 640,000 Palestinian children in Gaza against polio, an ambitious effort amid a devastating war that has destroyed the territory’s healthcare system.

The campaign comes after the first polio case was reported in Gaza in 25 years — a 10-month-old boy, now paralyzed in the leg. The World Health Organization says the presence of a paralysis case indicates there could be hundreds more who have been infected but aren’t showing symptoms.

Most people who have polio do not experience symptoms, and those who do usually recover in a week or so. But there is no cure, and when polio causes paralysis it is usually permanent. If the paralysis affects breathing muscles, the disease can be fatal.