A success story. The struggle against polio, which has triumphed to the point where it will soon, like smallpox, be declared extinct, is another remarkable story. Yet the disease, which spreads when traces of infected faeces are ingested, acquired an epidemic nature in the 20th century only in developed countries when strict hygiene had become the norm. Previously, polio had been endemic, and most children had caught mild, symptomless forms of the disease before they were five, gaining immunity. It could be argued that a victory had been gained over an epidemic humankind unwittingly brought on itself.
Polio carries with it another lesson.
It was still not clear by the end of the Royal Society conference whether there is a link between the African polio vaccinations and the success of the different strains of HIV in jumping species from monkeys and chimpanzees into humans and then spreading. The vaccine was grown in rhesus monkey cells at a time when the risk of animal viruses spreading to humans was poorly understood. So far there is little evidence that SV40 has done any harm, but it was a lucky escape. The dangers seem as great as ever. But our recently acquired knowledge of how viruses and cells work on a molecular level, particularly the breaking of the genetic code of different organisms, has greatly advanced the field of virology.