Polio is finding its way back to countries where it had been eradicated, and this time the disease is affecting mainly adults.
With 19 confirmed cases in Namibia, and another 150 unconfirmed ones, doctors are warning that the disease is targeting adults who had probably missed childhood vaccination, and have thus not developed a natural immunity by encountering wild forms of the virus.
The World Health Organisation warns that since many adults do not have immunity to the disease in countries where it had been eradicated, there may be more susceptible people now than at any other time in history.
Bruce Aylward, head of the WHO's polio eradication drive, said that the new findings showed the need to eradicate the disease in the whole world, for individual countries free of polio were now at risk.
"This just shows that we have to eradicate polio everywhere, because while endemic areas persist, the virus will find susceptible people," the New Scientist quoted him, as saying.
People can become immune to polio in three ways: by being infected naturally, by vaccination or by catching the live but weakened virus in oral polio vaccine (OPV) from newly vaccinated children.
However, while natural infection is disappearing, vaccination rates are also dropping in many countries as the disease continues to be eradicated. Along with this, the third method has also been abandoned from around 35 industrialised countries that have switched from OPV to a safer killed-virus vaccine that doesn't spread, leaving a growing number of people at risk.
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