Two shootings in northern Nigeria have left nine female polio vaccinators dead, in what is thought to be the latest violence by militant Islamic group Boko Haram, reports the BBC. Both attacks were carried out by gunmen riding on a motor tricycle, though it is not clear yet if the same individuals were involved. Islamic leaders in northern Nigeria have opposed polio vaccinations since 2003, claiming they could lead to infertility and AIDS, reports Reuters. Polio is still endemic in just three countries: Pakistan, Afghanistan, and Nigeria. The shootings happened in and around Kano, the area where 200 children were killed and others maimed by Pfizer's trials of its antibiotic Trovan in 1996.