Polio, a deadly disease that used to paralyze tens of thousands of children each year, is spreading in London, New York and Jerusalem for the first time in decades, spurring recovery vaccination campaigns.
Polio terrified parents all over the world during the first half of the 20th century. It mainly affects children under five years of age, is often asymptomatic, but can also cause symptoms such as fever and vomiting. About one in 200 infections leads to irreversible paralysis, and among those patients, up to 10% die.
There is no cure, but since a vaccine was found in the 1950s, polio is completely preventable. Worldwide, the wild form of the disease has almost disappeared.
Afghanistan and Pakistan are now the only countries where the highly infectious disease, which spreads mainly through contact with fecal matter, remains endemic. But this year imported cases were also found in Malawi and Mozambique, the first in those countries since the 1990s.
There are two main forms of poliovirus. Along with the wild type described above, there are also rare cases of what is known as vaccine-derived polio.
It is this second form detected in sewage in the British capital, London, and in New York in the United States, with a case of paralysis reported in the state of New York. A genetically similar virus has also been found in Jerusalem, Israel, and scientists are working to understand the link, the Global Polio Eradication Initiative (GPEI) said.
While vaccine-derived polio is almost unknown in the places mentioned above, it is a known, if rare, threat in other countries, causing outbreaks every year, including 415 cases in Nigeria in 2021.
It is derived from the use of an oral polio vaccine that contains weakened live virus. After children are vaccinated, they shed the virus in their feces for a few weeks. In undervaccinated communities, this can spread and mutate back into a harmful version of the virus.
While countries like Britain and the United States no longer use this live vaccine, others do, particularly to stop outbreaks, allowing global spread, particularly as people began to travel again after COVID-19 experts said.
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But experts agree that the main driver behind vaccine-derived and wild polio outbreaks remains undervaccinated populations, said Derek Ehrhardt, global polio leader at the Centers for Disease Control and Prevention ( CDC) of the United States.
Vaccine hesitancy was a growing problem before the pandemic, then COVID-19 caused the worst disruption to routine immunization in a generation, according to the United Nations.
In 2020, there were 1,081 vaccine-derived polio cases, about three times more than the previous year. So far in 2022, there have been 177 cases, after extensive efforts to restart polio vaccination campaigns.
But the sewage findings remain a wake-up call for parents with a key message, according to scientists around the world, including David Heymann, an epidemiologist at the London School of Hygiene and Tropical Medicine: Protect children by vaccinating them.
Edited by Mark Heinrich