Last week’s killings are believed to be the first time polio workers have been attacked in Nigeria, but opposition to vaccination campaigns is nothing new. In 2003, Muslim leaders in northern Nigeria said polio inoculations could cause infertility and AIDS.
Their opposition was blamed for a resurgence of polio in parts of Nigeria. But diseases do not respect geographical boundaries and polio promptly spread to other African countries which had already eliminated the virus and were forced to wage war on polio for a second time.
In Pakistan, Taliban militants have denied responsibility for the polio killings there, but they have repeatedly said the vaccination drive is a plot to sterilise Muslims or spy on them.
It is now incumbent on religious leaders and local authorities in all three countries where polio persists to debunk the sterilisation myth once and for all, as well as all other rumours that stop parents getting their children vaccinated.
The attacks in Pakistan and Nigeria should spur everyone to redouble efforts to stamp out the disease.
Oyewale Tomori, a campaigner in Nigeria, told Reuters the killing of the health workers would set back polio eradication, but would not stop it.
"The best we can do is to work harder and see the end of polio ... so their loss will not end as a useless sacrifice," he added.
Commenting on the killing of vaccinators in Pakistan, Gates made a similar point.
“They are heroes, and there are two ways to memorialise them,” he said. “The first is to do our best to ensure the safety of those who continue the campaigns. And the second is that we have to finish the task they gave their lives for.”