For years, global health officials have used billions of drops of an oral vaccine in a remarkably effective campaign aimed at wiping out polio in its last remaining strongholds – typically, poor, politically unstable corners of the world.
Now, in a surprising twist in the decades-long effort to eradicate the virus, authorities in Jerusalem, New York and London have discovered evidence that polio is spreading there.
The original source of the virus? The oral vaccine itself.
Scientists have long known about this extremely rare phenomenon. That is why some countries have switched to other polio vaccines. But these incidental infections from the oral formula are becoming more glaring as the world inches closer to eradication of the disease and the number of polio cases caused by the wild, or naturally circulating, virus plummets.
Since 2017, there have been 396 cases of polio caused by the wild virus, versus more than 2,600 linked to the oral vaccine, according to figures from the World Health Organization and its partners.
“We are basically replacing the wild virus with the virus in the vaccine, which is now leading to new outbreaks,” said Scott Barrett, a Columbia University professor who has studied polio eradication. “I would assume that countries like the U.K. and the U.S. will be able to stop transmission quite quickly, but we also thought that about monkeypox.”