Polio follow-up: Polio-free and then not

I talked on Monday about the risks to the worldwide polio eradication campaign of vaccine-derived polio (VDPV), the mutated form of the vaccine virus. New bulletins from the World Health Organization and the Centers for Disease Control and Prevention remind us that original wild polio can bounce back in perilous ways as well.

The WHO said Thursday that Congo, which saw its last case of wild-type polio in 2000, is in the midst of an outbreak that so far has racked up 120 cases of paralysis and 58 deaths, with half the cases occurring just in the last 10 days. (That’s the Republic of Congo, AKA Congo-Brazzaville. As distinguished from the Democratic Republic of the Congo, AKA the former Zaire, with which it shares a border. Clear?) In polio circles, every case of paralysis is taken to represent from 150 to 200 cases in which people experience no symptoms but are still carrying and transmitting the virus — so this outbreak is very large, and still growing.

Unfortunately, it is not the only one. In an article Thursday in its weekly bulletin, the Morbidity and Mortality Weekly Report, the CDC enumerated the countries other than Congo in which polio has reappeared over 21 months, from January 2009 to September 2010. It’s a dispiriting list: Benin, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Cote d’Ivoire, DR Congo, Guinea, Kazakhstan, Kenya, Liberia, Mali, Mauritania, Nepal, Niger, Russia, Senegal, Sierra Leone, Tajikistan, Togo, Turkmenistan and Uganda.

In each case, the countries had been free of sustained polio transmission for 12 months (Chad, DRC) or much longer (everywhere else). And because new polio cases seemingly ceased to be a risk, vaccination was allowed to lapse, or surveillance moved lower down the endless list of public health priorities, or local physicians, when they saw a case of paralysis, assumed that it could not be polio, and so did not send the virus for the appropriate tests.

And thus the countries were vulnerable when the virus walked or drove or flew back across their borders in the guts of someone unknowingly infected.

In some cases, it came a long way. One of the dark marvels of the polio eradication effort is the precision with which it can track the origin of a polio infection. Among the importations over the past two years, Liberia was infected by a strain from Guinea, Senegal was infected by Mauritania, Niger was infected by Nigeria, and Uganda was infected by the Sudan.

Those make sense, in a way; all those countries share borders. But Tajikistan was infected by a strain from India — and Tajikistan’s outbreak, which began in February, spread in turn to Russia, Kazakhstan and Turkmenistan. There have been 476 cases in those four countries so far.

The Tajikistan outbreak in particular — which brought polio back not only to a polio-free country, but to an entire region of the globe that had seen no cases in 8 years — underlines what it takes to beat back polio’s relentless advance. To control spread, the country mounted four separate national immunization days that each aimed to inoculate 98 percent of children — those under 6 for the first two days, and those under 15 for the next two. Then they did regional vaccination campaigns in 34 districts of the country; another national vaccination day last month; and they have yet another national vaccination day scheduled for this month. Hundreds of thousands of children, millions of doses and dollars.

The key point, for those who think of Tajikistan and Senegal as unimportantly far away, is that on a planet in which 80 million people travel to or from the developing world in a year, nowhere is far away. Roughly a half-million people from Tajikistan visited 250 countries last year, according to the CDC. The Canadian Medical Association Journal said back in June, when the Tajik outbreak was only 183 cases:

Too many regions and communities have ceased to worry about polio. As a consequence, rates of vaccine uptake are all too often well below effective prevention levels… Regions of Canada and some European countries have very low rates of vaccine uptake. Infants and toddlers are often not vaccinated on time because of a lack of appreciation of the seriousness of poliomyelitis… In all countries certified as polio-free… the Tajikistan outbreak should be clanging alarm bells.

Image courtesy Flickr user OrangeAcid under CC


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