Until about a year ago, a world free
of poliomyelitis seemed to be
imminent. In 1988, about 350,000
people in 125 countries became paralysed
by the virus. Last year, only 406 cases were
reported, with 160 of them in just a few areas
of the three countries where polio remains
endemic: Afghanistan, Nigeria and Pakistan.
In April 2013, charities and governments
pledged US$4 billion to a six-year plan
developed by the World Health Organization
(WHO) to eradicate polio. In March,
after India had gone three years with no new cases, the WHO certified its southeast Asia
region (which does not include Afghanistan
and Pakistan) as polio-free.
But in May, the WHO declared polio an
international public-health emergency, particularly
because of the high risk of international
spread from Pakistan, Cameroon and
Syria (see go.nature.com/ 7z3efj). Disrupted
vaccination programmes in war-torn places
are partly to blame.
Confronted by this, the WHO took an
unprecedented step: it called for mandatory
polio vaccination for everyone travelling toor from Pakistan, Syria and Cameroon, and
encouraged travel vaccinations for Afghanistan,
Nigeria and others1
. Formal international
travel restrictions for Pakistan began
on 1 June. Analyses in the past few years
show2
that symptom-free adults transmit
polio at surprisingly high rates. However,
computer modelling described3
earlier this
month suggests that immunizing adults to
control an outbreak is less effective than previously
believed