Polio is transmitted by poor hygiene and largely affects children
under five. In 5-10% of cases, the virus affects the nerves, paralysing
the legs in particular. For most, this is temporary. For others-30 years
ago, this was 350,000 children a year-paralysis is permanent, and if it
is of the lungs, they die.
In the early 20th century epidemics were frequent. When, in 1995, a
vaccine was developed, the British held street parties. Polio was declared
gone in the Americas in 1994; in the western Pacific region in 2000; in
Europe in 2002; India and south-east Asia in 2014. Last week, Africa
joined their number.
The global project has involved 20 million volunteers vaccinating nearly
3 billion children. It is an amazing achievement. But it is still fragile,
for a number of reasons.
First, what is being eradicated is wild polio. It's still possible to
get vaccine-derived polio, where the much-diluted active components spread
through an under-vaccinated community and, in rare cases, revert to the
full-blown disease.
Second is disruption. In Africa, the last 1% proved hardest partly because
of war and anti-vaccination sentiment.
Third, eradication is in its final, most delicate, stage. The vaccine, a
droplet-administered method that contains active virus and confers lifelong
immunity, must eventually be replaced by injections of inactive strains in
order to cancel all risk of vaccine-derived polio virus.
In this year, there is much that feels familiar about the story of polio
-from stealthy onset to hopes for a vaccine, to worries about anti-vaxxers.
But we must take other lessons too: that eradication could take years of
patient vigilance. That we are capable of great things. And that we must
be prepared.