Polio in US, UK and Israel reveals rare risk of oral vaccine
- Genetic analyses show the infections are all ‘vaccine-derived’, meaning they are mutated versions of a virus that originated in the oral vaccine
- The oral vaccine contains a weakened form of the live virus; in very rare cases, it can mutate into something more dangerous and spark outbreaks
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.
“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 UK and the US will be able to stop transmission quite quickly, but we also thought that about monkeypox.”
The latest incidents represent the first time in several years that vaccine-connected polio virus has turned up in rich countries.