Existing polio vaccines may not always prevent infection

A new study has shown that the standard polio vaccine may not always be able to prevent people from getting infected with the virus.

To prove this, the study that was published in PLOS ONE took the case of the disease outbreak in The Republic of Congo in 2010. The reason the vaccine didn't work there was that the virus had mutated, the researchers said. The outbreak had a fatality rate of 47 per cent. Though previous studies have suggested that this unusually high rate of deaths occurred because people were not vaccinated, Drexler said. But the new study suggests that the lack of immune-system response in people who were vaccinated also played a role.

In the study, the researchers looked at blood samples taken from 75 people who were vaccinated against polio. Twenty four of them died from polio in the outbreak, and 51 others, from Bonn, Germany, were polio free.

The researchers isolated the virus from the blood of one patient who died from polio. They found that the virus that killed the person was a mutant strain, meaning it was genetically different from other polioviruses seen before. They also concluded that the antibodies normally produced in response to infection were unable to block the mutant virus.

The findings show that researchers need to identify mutant virus strains and generate more potent polio vaccinations, said study leader Dr Jan Felix Drexler, a virologist at the University of Bonn Medical Centre in Germany. "On one side, we have mutant viruses that are out there, and on the vaccine side, we need to continue generating vaccines and thinking about new ones," Drexler said in a report published on website Live Science. "We proved the mutant viruses are out there, but if we provide robust population immunity, we can still stop the viruses from causing disease," the researcher added.

Explaining the limitations of the study, Drexler said the research team had no access to the clinical histories of the patients who died of polio in the Congo outbreak, making it hard to tell how they had reacted to the vaccine. Therefore, a further research needs to be conducted on the same. 

International spread of virus continues

In a related development, a new case was detected in Pakistan on Tuesday, taking the total number of confirmed polio cases in the country this year to 117.
According to the World Health Organization (WHO), poliovirus from Pakistan has recently spread to Israel, West Bank and Gaza, and Iraq. Apart from these countries, Nigeria and Afghanistan are not yet free from the disease.

Meanwhile, in India, nearly five months after declaring the country free of polio, the WHO is now focussing on implementing a risk-free withdrawal of the oral polio vaccine and introducing inactivated polio vaccine.
 

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