Two genetic mutations in the polio virus have raised the spectre of the virus gaining advantage over vaccines. Institut Pasteur / C. Dauguet

Just as the global campaign to eradicate poliomyelitis is entering its final phase, researchers have traced recent outbreaks of polio in the Republic of Congo to two genetic mutations in the virus.

This further complicates attempts to eradicate the debilitating disease.

Antibodies produced by the immune system of the vaccinated patient will not be able to recognise the new viral strains, says the study done by IRD (Institut de recherche pour le développement).

The researchers tested the variant of poliovirus on blood samples from more than 60 vaccinated people.

The antibodies were shown to be less effective against the Congo strain than against the other strains of poliovirus. The researchers estimate that 15%–30% of these people would not have been protected during the 2010 Congo epidemic.

The researchers are calling for better clinical and environmental monitoring to completely wipe out the scourge of polio.

The global initiative to eradicate poliomyelitis through routine vaccination has helped reduce the number of cases by more than 99% in 30 years, from an estimated 350,000 cases in 1988 to 650 reported cases in 2011.

However, major epidemics are still occurring today.

The epidemic outbreak in 2010 in the Republic of the Congo differed from the cases found in Tajikistan in 2010 and China in 2011 in its exceptionally high mortality rate of 47%: out of the 445 confirmed cases, nearly 210 died.

Low vaccine coverage was first suspected till the IRD team sequenced the Congo virus DNA and discovered the mutations.

Sudden paralysis in children is a hallmark of the polio virus but this can also be caused by other infectious organisms, congenital problems, exposure to toxic chemicals and more, says NPR.

In polio surveillance, health officials look for a sudden paralysis rate in children under 15. Low reports often mean there is not much surveillance.

Missing a single case could send polio numbers ballooning. "If we take our eye off the ball we're up to 200,000 cases a year in the next ten years," says Carol Pandak, global director of Rotary International's Polio Plus Program.