Polio was a major health problem in the late 1990s, infecting about 350,000 people in more than 125 countries by 1998. After international efforts were introduced that combined routine immunisation with high-level surveillance, the number of cases fell to 784 in 2003. But Nigeria's decision that year to suspend all polio vaccinations for 12 months threatened to reverse this progress.
The eradication of the disease is now back on track. But as Bruce Aylward, Roland Sutter and David Heymann say in this article, several challenges will remain even after the disease has been wiped out.
The most widely used polio vaccine contains a live virus. While this is used, say the authors, there is a risk that it could cause outbreaks as happened recently in China, Indonesia and Egypt. Stopping vaccination could also be risky, because the virus — which can cause paralysis — might still be circulating in some individuals.
The authors make a number of recommendations about how to safely halt vaccination with the live virus.
The first is the need for confirmation that the poliovirus is not being transmitted anywhere in the world. Existing stocks of poliovirus — including a stockpile to respond to a re-emergence of the virus — must also be kept well contained. They also stress the importance of collaborative international agreements on how to stop vaccination, and the need for surveillance efforts.
The decision about whether to vaccinate with an inactivated — but much more costly — vaccine will be a difficult one, especially for poor countries, they add.