LONDON (AP) — The World Health Organization says the ongoing attempt to eradicate polio remains a global emergency amid an increase in cases for the first time in years and a worrying number of outbreaks sparked by the vaccine.

After an expert meeting convened by the U.N. health agency this week, experts said Friday that failing to wipe out polio in the next few years could lead to a resurgence of the crippling disease. An international initiative to eradicate polio began in 1988 but efforts have stalled in war-torn countries and WHO and its partners have missed repeated deadlines to stop the virus.

WHO said the polio epidemics in Afghanistan and Pakistan were particularly worrying. The number of cases in Afghanistan has almost doubled this year and polio is increasingly being found in the environment.