Why has polio returned to London and New York?

Poleomyelitis (or polio.), in short) terrorized America and Europe until the 1960s. It paralyzed more than 15,000 people each year in the US and 8,000 in the UK, mostly children. There is no cure for polio and 5-10% of paralytic cases are fatal. The invention of the vaccine put the world on the path of elimination. In 1994 the territory of the US was declared free of wild poliovirus. Europe followed in 2002 and Africa in 2020. But in June a 20-year-old man was paralyzed by polio in a New York City suburb. This was the first confirmed case of local transmission in the US since 1979. In recent months, poliovirus has been found in samples of wastewater in London and New York to indicate that the virus is spreading there. Why has polio returned?

Today, wild poliovirus is endemic only in pockets of Afghanistan and Pakistan. The type found in London and New York is a vaccine-derived strain, a rare mutation resulting from the oral polio vaccine. Unlike the jab used in Western countries, which is based on an inactivated virus, the oral vaccine contains a weakened strain of the live virus. It is still used in poor countries for several reasons. First, it is cheap and easy to administer. Second, a person who takes an oral vaccine can transmit immunity through “passive vaccination”: They shed the weakened virus in their feces for a few weeks after vaccination. If an uninfected person swallows particles of the virus (which is common in places with poor sanitation) that person is also vaccinated.

But this secondary benefit comes with a big risk. If the vaccine-derived virus continues to spread among unvaccinated people, it slowly turns into a harmful form that can cause paralysis in about one in a thousand infected people. This process of mutation usually takes a year or so. Due to inadequate vaccination rates, outbreaks of vaccine-acquired polio are most common in Africa. Occasionally, outbreaks have occurred in parts of Asia and the eastern Mediterranean. It is one of three regions where the poliovirus spreading in London and New York was probably imported.

Polio is now spreading in both cities when people swallow particles from the feces of an infected person. If an infected person does not wash their hands after using the toilet, or a caregiver fails to do so after changing an infected child’s nappy, they may eat food or other objects (such as toys that other children have touched) Touching can spread the virus. put in their mouth) and through a handshake. Both oral and inactivated vaccines prevent paralysis. But they are not particularly good at preventing this kind of transmission. The idle jab is particularly bad at this. The protection of oral vaccines against transmission is strong at first (very good for outbreaks) but is relatively short-lived. About twenty years ago America and Europe stopped using it.

This means that some vaccinated people in London and New York may be part of the polio transmission chain, although non-vaccinated people are more likely to spread the disease because they shed the virus longer. The cities in London that contain the most polio virus in wastewater samples have some of the lowest polio vaccination rates.

The worry now is that if polio continues to spread at a high rate, polio will paralyze some illiterate children. The paralyzed youth was not vaccinated in America. A lot of infections go unnoticed because paralysis is so rare. About 70% of unvaccinated people will have no symptoms and the rest will have only mild flu-like symptoms. Vaccination campaigns, including boosters, were recently launched in London and some New York counties. New York City doctors have been told to contact parents of children who have not been fully vaccinated.

In 2020 the World Health Organization approved a new form of oral polio vaccine. It contains a polio virus that has been genetically engineered to prevent it from becoming harmful but still has the secondary benefit of passive vaccination. The new vaccine is now being used for large-scale vaccination campaigns in African and Asian countries with polio outbreaks. As its supply increases, it will completely replace the older oral vaccine. This will prevent the further emergence of vaccine-derived strains. But those already moving to New York and London, two of the world’s busiest travel hubs, could spread far and wide.I

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