In the 1970s, public health workers around the world organized a successful effort to eradicate smallpox. But a more recent effort to wipe out polio has so far failed.
Why hasn't the program to end polio succeeded? And what can be done to improve the chances of success?
Columbia University professor Scott Barrett writes about the challenges facing polio eradication in the current issue of the journal Health Affairs. Barrett says the effort to wipe out smallpox could easily have failed.
"First of all, it barely succeeded. You know, these things, when they happen, we sort of take them for granted, which is why you need to read history. And the history of smallpox shows that it was a very close call and may not have succeeded and to some extent we're fortunate that it did."
Like smallpox, polio is a highly contagious disease. The battle against it began in earnest around 50 years ago, when two different vaccines were developed — first, an injectable vaccine that used a dead polio virus, and then one that used a weakened but live virus. The live-virus vaccine, which is given by mouth, is a lot cheaper, but can actually cause polio in a very small number of cases.
Efforts since the 1950s to eradicate polio have achieved remarkable success, but the disease stubbornly persists in a handful of places, and Barrett says that eliminating polio from those remaining pockets is challenging and may not succeed.
"This time around, there's no date given for when eradication will actually be achieved," says Barrett. "Dates have been given twice before and missed twice before. So this time around, dates have not been given. So it's a gamble. We may win; we may not win."
That said, he identified a number of challenges to the complete eradication of polio in the regions where the disease remains endemic.
In the Afghan-Pakistan border region, eradication programs face factional fighting and sometimes-violent opposition to vaccination.
In two northern states in India (Uttar Pradesh and Bihar), vaccination can fail to protect children who have other virus infections or diarrhea.
And in Northern Nigeria, vaccination was suspended in 2003 after political and religious leaders claimed the vaccine was contaminated with HIV among other things.
Barrett says another issue is the risk of polio escaping from the hundreds of labs that maintain samples of the virus.
"There is polio in laboratories all over the world. And the eradication initiative is again taking steps to identify these samples and either have them destroyed or have them stored under strict biosafety standards. So there will be a risk of reintroduction from laboratories. And again, there are examples where this has happened in the past with other diseases, including smallpox."
Funding an expensive eradication program is another challenge. The Nigerian boycott prompted the European Union to temporary stop donations. Officials estimate more than $2 billion will be needed over the next few years to fund the vaccination effort. But Barrett describes disease eradication as an investment.
"You undertake eradication not only to prevent from getting disease in the future, and of course there's a return we get on that, but also to avoid the need to vaccinate in the future," Barrett says.
That's known as "the eradication dividend." Barrett stresses that eliminating polio will have benefits beyond those gained in the areas where it currently remains a threat.
"Our fates, in many ways, are so interlocked. This is a good way to understand the concept of globalization. What goes on in small villages in a remote part of Nigeria will determine a return that we're going to get here in the United States as well as elsewhere."
But Columbia University's Scott Barrett says that even if polio is wiped out, the world will have to maintain vigilance against a potential reemergence of the disease.
"After eradication has been achieved — let's hope it will be achieved — and has been certified, there's always the risk that it will break out again, and then the post-eradication risk will depend on our ability to jump on it and suppress it before it has had a chance to spread."
Scott Barrett spoke in Washington at an event sponsored by the journal Health Affairs, where his paper appears in the current issue.