A woman is vaccinated at a health center in Conakry, Guinea, during the clinical trials of a vaccine against the Ebola virus.

When Ebola struck West Africa a few years ago, the world was defenseless. There was no cure. No vaccine. And the result was catastrophic: More than 11,000 people died. Nearly 30,000 were infected.
Now it looks like such a large outbreak is unlikely to ever happen again. Ever.
The world now has a potent weapon against Ebola: a vaccine that brings outbreaks to a screeching halt, scientists report Thursday in The Lancet.
“We were able to estimate the efficacy of the vaccine as being 100 percent in a trial with more than 5,000 people,” says Ira Longini, a biostatistician at the University of Florida, who helped test the vaccine. “It’s very unusual to have a vaccine that protects people perfectly.”
Now, no vaccine — or drug for that matter — is perfect. And efficacy of the vaccine is clearly high but not “100 percent.” That value reflects the fact that they just haven’t tested …
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