The polio virus fights back

[bemildred]

Sabin's oral vaccine is actually causing new outbreaks of the disease.


We've been waiting a long time for the eradication of polio. Since the World Health Organization's 1988 decision to eliminate polio from nature, as it once did smallpox, billions of dollars have been funneled into this long war. The Bill & Melinda Gates Foundation alone has contributed more than $1 billion since 1999 to the effort, and it recently pledged an additional $119 million. The massive campaign has included armies of eradicators, mountains of research and the dedication of numerous governments and NGOs.

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Last year was a good one for polio eradication. Nigeria, long a pool of infection, has vigorous new leadership dedicated to the campaign, and this has led to a sharp reduction in polio there. Transmission of the disease has nearly ceased in two other holdout areas: the states of Uttar Pradesh and Bihar in India.

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How can the oral vaccine, which has saved so many lives, also be a villain? Very rarely, it causes something called vaccine-acquired paralytic polio. The risk of getting this form of polio from the vaccine is minuscule — perhaps one case per million. But it is real. The threat of it caused the U.S. to switch to inactivated vaccine more than a decade ago.

And there is an even bigger risk with the oral vaccine: what happens to it after it leaves the human who was vaccinated. According to Columbia University virologist Vincent Racaniello, as soon as the vaccine is shed in stool, it's no longer simply a vaccine virus. It begins to evolve back to virulence, and this can be a big problem in countries where sanitation is poor.

http://www.latimes.com/news/opinion/commentary/la-oe-orent-polio-20110209,0,1392481.story

[pnwmom]

1. Ironically, the shed virus used to be considered an advantage

of the oral vaccine -- it was considered to advance "herd immunity."

But we had unvaccinated elderly relatives living in a rural area, so we made sure our child got the killed virus-- when the live virus was still standard-- even though we couldn't get it through our doctor. We had to wait for hours at the public health department to get it. By the time our third child was born, the recommendation had changed to the killed virus vaccine, at least for the first dose. After that, it could be switched to the oral.

[bemildred]

2. Well, I think the message here is that one in a million can be enough.

When it comes to evolution, one in a million translates into rapid change.

[pnwmom]

3. And the number is actually higher than one in a million.

The one in a million referred to the chance that a vaccinated infant would get the disease. The number is higher for those who catch the disease as a result of the shed virus -- as is shown by the scattered outbreaks.