Polio Eradication: Harder Than it Looks

Why it might require a new vaccine

The global campaign to eradicate polio crushed 90% of the disease in the space of a dozen years, by 2000. In the decade since, complete elimination has swung tantalizingly close—and then away again when case counts spiked and outbreaks reappeared in countries recently cleared of the virus. Once again, cases are ebbing and hopes rising. The New York Times recently reported that for four straight months, India has seen no new cases in its two most polio-burdened states. But the real news is the unnoticed opening of a new scientific front in vaccine research, portent of a longer battle.

The polio-free streak in the state of Uttar Pradesh, while encouraging, is actually only two months old and in the state of Bihar just over three. India as a whole did have zero cases in March. But in four of the last ten years, the country has started off with even fewer total polio cases only to see the tide turn. Nationwide, the total cases so far this year, 19, equals the number at this time in 2009. Polio incidence usually rises in May; given reporting delays, by July, the direction of the trend should be clearer.

The Times article cites extraordinary vaccination efforts to explain the new swing toward eradication. Polio vaccination campaigns in India are monumental undertakings, war-sized in scale involving an army of over two million vaccinators going house-to-house and overseen by a supervisor corps numbering greater than 100,000. However, the most enduring reason polio continues in India has not been a failure to vaccinate, but a failure of the vaccine.

If the population covered by campaigns is increasing, so too is the frequency of the campaigns. Vaccinations became monthly in Uttar Pradesh, for example, in 2007 in order to cover more quickly the 500,000 children born there each month.

Although the remarkable vaccination efforts have greatly pushed down polio cases, eradication has remained elusive because eight vaccine doses or even more don’t necessarily confer immunity. In India, the number of polio cases where the individual hasn’t been vaccinated has plummeted toward zero. Instead, increasingly the victims have been vaccinated over and over—to no effect.

In most places in the world—and many places in India—the Sabin oral polio vaccine works after two doses. No one knows what makes it go awry in Uttar Pradesh and Bihar. Those states are highly populous but low in income. Overcrowding and hygiene conditions help infection spread. But the vaccine's inability to elicit immunity is thought to be a product of malnutrition, immune suppression caused by other diseases and possibly genetic factors.

The World Health Organization just closed a call for research proposals to find out why, part of an ongoing large investment in improved vaccines. Critics of the eradication program have vociferated about the oral vaccine for some years. But developing new vaccines or drugs is time consuming, costly and not guaranteed to work, perhaps explaining the reluctance to open a scientific front in the war on polio. Previously, global eradication, while hugely daunting and complicated, came down to logistical execution, will power and funding.

Bruce Aylward, who heads the eradication effort at the World Health Organization, has ample willpower, but worries constantly about finances. He has steadily forecasted the imminent demise of polio for years. To fund the pursuit of eradication, he has learned that when there’s good news, like a favorable turn in case numbers, you cash it in. Aylward told the New York Times: “We’ve never had so many things looking so positive across so many areas.” Concerning a funding shortfall, he hastened to add: “I spend as much time in donor capitals as I do in infected countries.”

Hopefully his efforts will pay off. But if eradication remains unachieved, we will almost certainly be on the verge of it—still.


Photo credit: Jean-Marc Giboux via quilty2010, Sub-National Immunization Day. Lucknow, Uttar Pradesh

Source, 2nd graphic: AFP Surveillance Bulletin—India Report for the week ending February 6, 2010

Source, 3rd graphic: Paul, Y., Polio eradication in India: Have we reached the dead end?, Vaccine.  2010 Feb 17;28(7):1661-2.



Polio Turns Stealthy in India (August 19, 2010)

Heavy Lifting: Raising Health Beyond Polio's Reach (May 13, 2010)

Wall Street Journal: Pulling the plug on polio eradication? (April 26, 2010)

3 responses
The graph would certainly suggest there is no eradication imminent. ANy worries about polio developing resistance?
There is a huge volume of oral polio vaccine being poured into the world but, perhaps because there is relatively little polio, the only new variants of the virus have actually come from the vaccine.

The oral vaccine uses an "attenuated" virus which can mutate back into a disease-causing strain. It has several times over in a number of places around the world.

Vaccine-derived polio is another reason eradication is tricky. The vaccine is being used to bring about eradication but itself is the source of some outbreaks of the disease. The Salk vaccine doesn't have this problem but it is more expensive, uses a needle (so is much harder to use in mass vaccination) and also provides a different kind of immunity--it goes into your bloodstream and not down your gastro-intestinal tract, which is where the virus travels.

Thanks so much for your article, very helpful info.