Vaccine-derived poliovirus, which is found particularly in Africa and Asia, comes from a widely used oral vaccine that contains a live, weakened virus that sometimes mutates into a dangerous form capable of infecting the nervous system. However, the United States and the United Kingdom use an injectable vaccine containing the inactivated virus, which can prevent the virus from infecting the nervous system. But it is not as effective as the oral vaccine.
The dreaded polio virus
Polio has no cure and causes irreversible paralysis in fewer than one in 200 of the susceptible people it infects. But since a vaccine was found in the 1950s, polio is completely preventable. Globally, the wild form of the disease has almost disappeared. Afghanistan and Pakistan are now the only countries where the highly contagious disease, which is spread mainly through contact with faeces, remains endemic. But this year, imported cases were detected in Malawi and Mozambique, the first in those countries since the 1990s. (Also read: Polio fears rise in New York amid possible community spread) There are two main forms of the polio virus. In addition to the wild type, there are also rare cases of vaccine-derived polio. It is this second form that is detected in sewage in London and New York. A similar virus has also been found in Jerusalem and Israel. Now, in an interview, the British weekly science magazine Nature has spoken to researchers about the scale of the epidemic and what can be done to stop it. Walter Orenstein, who studies infectious diseases at Emory University in Atlanta, told the journal that “the virus is very, very good at finding unvaccinated people.” While vaccinated children are spared the worst effects of the virus, unvaccinated people are vulnerable to the disease. Orenstein added, “In New York, the virus has been detected in two counties as well as in New York, a geographic spread that is very concerning. It suggests we’ve had significant transmission.” However, in London, the virus appears to have remained concentrated in the north and east of the city, said infectious disease epidemiologist Nicholas Grass at Imperial College London. In addition, the strengthening of vaccination efforts should fill the gaps caused by the Covid-19 pandemic and contain the outbreak in the United States, Israel and the United Kingdom. But drivers in London and New York will use the injectable vaccine, so they won’t stop transmission of the virus, Grassly told Nature. “If in six months or so, the sewage tests suggest that the polio virus has continued to spread, we may have to look at other options,” he added. For example, the WHO has registered a new oral polio vaccine for emergency use. However, the vaccine has yet to undergo large-scale human trials and has not been approved by UK or US regulators. But more than 100 million people have received it, says Andino-Pavlovsky, who helped design the vaccine.
