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Scientists Identify Vaccine-Resistant Polio Strain

vaccine resistang polio

Image credit: Institut Pasteur / C. Dauguet

Before the wide introduction of polio vaccine invented by Jonas Salk in 1955, the average number of Poliomyelitis cases was 35,000 every year just in the United States. Thanks to many efforts dedicated to vaccination, 2013 saw only 416 recorded cases all over the world. Although the global eradication will be soon achieved, unfortunately, in 2010, massive outbreak of polio occurred in the Democratic Republic of Congo (DRC), which resulted in the deaths of 47% of the 445 individuals who had been affected.

At the beginning, the outbreak’s severity was attributed to low vaccination rates in that area. However, after further investigation, it was found that the vaccination rate was quite high; it should prevent polio from being as prevalent as it was, especially for adults. Typically people were infected with poliovirus via contact with feces of patients, therefore lack of clean water access and overpopulation would be the main causes of the epidemic.

At the earlier time of this year, after analysis of virus’s genome, scientists discovered that a mutated strain was what they should consider to resolve. Actually, it was thought to be very closely associated with a mutant strain found in Angola in 2009. Jan Felix Drexler of the University of Bonn, the leader of research team had their result published in the recent edition of Proceedings of the National Academy of Sciences.

Researchers were now very clear of the truth of why the DRC epidemic was so fatal, the reason was because of resistance of the strain of poliovirus to vaccines. Such strain consisted of two mutations in the protective capsid, which would assist the virus to escape antibodies from the immune system.

After taking blood samples from more than 60 vaccinated volunteers from Germany and Gabon, a neighbor country of DRC, the researchers then exposed the blood to various strains of poliovirus, but they got some confusing results. The antibodies failed to work properly when they were faced up with the mutant strain which was blamed for the outbreak in 2010. Actually, when the vaccinated volunteers were exposed to the virus, 15-30% of them would be vulnerable.

As suggested by Drexler’s team, due to obvious existence of other mutated strains, the health officials should always on alert. In addition, although inoculation with previous polio vaccines could be much helpful in offering remarkable protection against the most common strains of the virus, it was still possible for vaccinated individuals to get infected with a new, mutated strain. In Drexler’s opinion, revaccination was very necessary for people to have better protection.

Thanks to great efforts from the dedicated health care workers, polio is now endemic just in the counties of Afghanistan, Nigeria and Pakistan. But the rise in polio cases in Afghanistan is closely linked with the number of attacks on health officials who are trying very hard to eradicate disease in the country.

However, the outbreak of polio in DRC as well as those occurring in China and Tajikistan has showed that infection could happen outside of these countries. So the discovery of a polio strain resisting vaccination could make these efforts definitely complicated. Though global eradication of the virus is expected to be very close, as long as it exists, it should be seen as a coming threat.

Source: UPI, IRD,

Journal reference: Drexler, Jan Felix, et al. “Robustness against serum neutralization of a poliovirus type 1 from a lethal epidemic of poliomyelitis in the Republic of Congo in 2010.” Proceedings of the National Academy of Sciences 111.35 (2014): 12889-12894.