Polio Season, Again

For the first half of the 20th century, every summer was polio season. Poliovirus, which spreads by the infamous “fecal-oral route,” thrives in sewage systems and contaminated waterways all year, but summer offers many more chances for exposure. Anyone swimming at a local beach or public pool routinely contracted it.

Most people who catch poliovirus develop nothing more serious than a mild diarrhea, but about one to two percent of them progress to the neurological disease that made polio one of the most feared infectious agents in the world. One or two percent doesn’t sound like much, but once the virus reaches a watershed, it can infect nearly everyone in the area, so that tiny percentage translates to a huge number of permanently paralyzed children, some of whom even die of the disease.

Polio Pointers for Parents, 1951

The Salk and Sabin polio vaccines brought an end to this era, and references to polio in modern times usually conjure images of iron lungs and FDR. Unfortunately, polio isn’t quite a thing of the past yet, and a misguided, drawn-out campaign by the World Health Organization to eradicate the disease may actually do more harm than good.

Many virologists – including me – have written detailed technical critiques of the WHO’s campaign, none of which have been adequately answered. At this point, the WHO effort seems to be sustained more by egos than sound public health planning. There are numerous flaws in their approach, and while my thesis advisor and I were the first to make a major public statement criticizing it, we were not the first to forsee these difficulties, nor the last to broadcast a warning.

This is one of those cases where it hurts to be right: we’re now seeing the tragic consequences we predicted a decade ago, and once again it’s polio season. Namibia kicked it off this year, with a major outbreak that ended ten polio-free years for that country. The authorities reacted quickly, with a mass immunization drive that sought to catch up with all the people who’d missed being vaccinated before. Since then, we have no more word on outbreaks from Namibia, but the disease also struck Afghanistan this year, and the prospects for organizing a major vaccination campaign in that devastated country are next to nil.

Both the Namibia and Afghanistan outbreaks highlight one of the problems we all saw coming: once the WHO finishes “eradicating” the disease in a country, they essentially turn off the lights and leave. Of course, that’s not the way they describe it, but that’s the net result. Local public health authorities in poor countries, generally overwhelmed by the triple tragedies of AIDS, malaria, and TB, and lacking any coherent backing from their own governments, cannot be expected to keep up with polio vaccination and surveillance. Predictably, vaccination rates decline, the disease gets reintroduced from nearby areas where it’s endemic, and an outbreak starts.

A more insidious problem – also predicted a decade ago – is the rise of vaccine-derived outbreaks. Indeed, several countries, most recently China, have seen sudden outbreaks of polio that actually came from the vaccine. That’s because the Sabin vaccine, which forms the backbone of the WHO eradication effort, produces virulent revertant viruses at a low but nonzero rate. In fact, there’s good evidence that people with compromised immune systems can continue to shed live, virulent poliovirus revertants for years after immunization with the Sabin vaccine. With a sizable portion of the world’s population suffering from immunodeficiency caused by AIDS, that adds up to a lot of chronic virus secreters.

That isn’t a big problem if vaccination rates are high, because the secreted, virulent virus won’t find enough susceptible hosts to spark an outbreak. However, once the WHO declares a country “polio-free,” the political will to continue expensive and unpopular vaccination drives evaporates. Vaccination goes out of fashion, surveillance lapses, and initially there are no consequences. After a few years, though, the number of susceptible hosts builds up high enough, and a vaccine-derived outbreak occurs.

What’s the solution? Stop trying to eradicate diseases and focus on controlling them instead. Even the eradication of smallpox, our only such victory, turned out to be a mixed blessing; if smallpox had faded more gradually, we might have continued developing safer vaccines, and we wouldn’t now be spending quite as many billions of dollars on a mushrooming “biodefense” industry to protect us from bioterrorism. Shifting from polio eradication to polio control would let us integrate this vaccine into a complete package of public health programs, and reinforce the lesson that public health isn’t something you do once and then forget about. We need to help poor countries build comprehensive long-term plans, rather than vast patchworks of Band-Aids.

Unfortunately, that kind of patient planning is done by big groups of people over long periods of time, and it isn’t a great way to advance an individual career. Instead, the folks leading the current WHO effort continue their eradication campaign, and outbreaks continue to strike. We’ll see how it goes next polio season.