Vaccine-Resistant Polio
On August  18, a study published in the Proceedings of the National Academy of Sciences discovered the cause of the particularly deadly 2010 polio outbreak in Congo: a mutated strain that is resistant to vaccination.

Of the 445 infected, almost half of them succumbed to the virus. The outbreak’s high death rate of 47 percent was originally attributed to low immunization coverage but is now thought to be caused by a mutated strain originating from Southeast Asia. The vaccine-resistant polio strain featured a combination of two mutations that both affected the proteins of the strain’s coat, effectively making it more difficult for the antibodies to recognize and stick on the virus.

The research team tested blood samples from Gabon and from German medical students that had been vaccinated. They found that their antibodies were less effective against the Congo variant and that approximately 15 to 29 percent of the students would have been unprotected from the Congo version.

The vaccine used in Congo and in most developing countries is a weaker, dead serum and was not sufficient in providing protection. In contrast, individuals that receive the live, oral polio vaccine are provided with the strongest immunity and are protected from this polio variant.

The spread in the Congo was stopped by the administration of oral vaccine to the entire population of the surrounding areas.

While the disease is only widespread in three countries, Nigeria, Afghanistan and Pakistan, the larger concern is that similar outbreaks will appear as the world is on the cusp of completely eradicating polio. Areas where dominant strains have been eradicated but vaccine coverage is low are at risk of mutated strains in particular.

However, there are a number of promising methods for prevention and the eventual eradication of polio.

By simply increasing vaccine coverage and surveillance, outbreaks can be detected earlier or completely prevented with high vaccine implementation.

In addition, double vaccination has also proved effective in boosting immunity. By combining the oral vaccine with an additional injection of the inactivated virus, the provided immunity is much more effective than the typical application of two drops of the oral vaccine.

On the other hand, there are still many barriers impeding efforts to eliminate polio.

Delays with updating the public database with the most recent poliovirus sequences have been impeding research among the wider scientific community.

Moreover, security issues in high-conflict regions where vaccination is used as a political tool prevent successful vaccination coverage. The effectiveness of the double vaccination approach is especially promising due to its efficiency under limited access. With a brief period of time, the double vaccination method achieves much more than with the oral vaccination method.

While much has been done to almost eradicate polio, there must still be efforts to achieve the complete annihilation of the virus.

– William Ying

Sources: Proceedings of the National Academy of Sciences of the United States of America, Nature, Yahoo News, Live Science, BBC
Photo: flickr