Pakistani officials said at least 15 people were killed and 20 others injured Wednesday after an explosion outside a polio vaccination center in the city of Quetta, the capital of Balochistan province. Many of the casualties were confirmed to be security forces guarding the clinic. Militant groups oppose polio vaccination, calling it a Western conspiracy to sterilize Pakistani children. The disease is still endemic in Pakistan, but on the decline. In 2015, 49 new cases of polio were reported, compared with 282 in 2014.