A virus that can rarely cause a polio-like paralysis in children has resurfaced in the US after mostly disappearing during the covid-19 pandemic. The Centers for Disease Control and Prevention reports that it has spotted a surge of cases linked to enterovirus D-68. Based on recent past outbreaks, officials expect that a small percentage of these cases will develop a serious neurological condition known as acute flaccid myelitis.
Over the weekend, the CDC issued a health advisory concerning EV-D68. Since August 2022, doctors and hospitals in several parts of the country have notified the agency of an increase in severe respiratory illness cases and hospitalizations among children caused by two groups of viruses: rhinoviruses and enteroviruses. Further testing has shown that some of these cases were caused by EV-D68, and the CDC’s own surveillance data has shown a higher proportion of respiratory illnesses tied to the virus this summer compared to the past three years.
EV-D68 is one of many viruses that usually cause a mild common cold, mostly in children. However, it’s become apparent in recent years that the infection can sometimes trigger AFM. The virus is a cousin of the poliovirus, which has long been known to cause a similar paralytic condition in about 0.1% of victims. And it’s suspected that EV-D68 has recently mutated in some way that makes it more similar to polio and thus more likely to cause AFM, although it is still a rare complication.
The primary symptoms of AFM are sudden limb weakness, and some will also experience facial weakness, slurred speech, and pain along their limbs and back. In the most severe cases, people can develop a life-threatening paralysis that causes respiratory failure, while others may develop permanent paralysis.
There are probably several causes of AFM, including other enteroviruses, but the spike in cases seen since at least 2014 is closely connected to outbreaks of EV-D68 in particular. These outbreaks of EV-D68 and AFM had occurred every two years on schedule during the past decade, likely as a result of population immunity falling low enough for large groups of children to catch it all at once. But this pattern, which would have predicted another AFM outbreak in 2020, changed once the covid-19 pandemic arrived.
While mostly everyone has contracted covid-19 by now, much of the world took precautions during the first years of the pandemic to avoid unnecessary social and physical contact. These efforts may have only slowed down the spread of the highly contagious coronavirus, but they were more effective at curbing the transmission of many other, less-contagious infections, EV-D68 included. It’s only recently that many garden variety germs have started to storm back in frequency, and experts have warned that EV-D68 would eventually follow suit as well. The virus tends to be seasonal, arriving in the summer, just as it has now.
There have been nearly 700 confirmed cases of AFM documented by the CDC since 2014, when the agency began formally tracking it. During past outbreak years, there were around 150 to 200 cases of AFM. So far, only 13 cases have been reported in 2022. But the condition typically appears weeks after the initial symptoms of a common cold, and past outbreaks of AFM have similarly followed outbreaks of EV-D68. In its advisory, the CDC calls for doctors to be on the lookout for the condition and notes that “increased vigilance for AFM in the coming weeks will be essential.”
The actual poliovirus has made something of an unwelcome return in the US this summer. In July, a young New York resident developed paralytic polio, and the virus has since been found in the state’s wastewater, indicating the potential for further spread. The virus may not spread very far, thanks to a highly effective vaccine and a high vaccination rate (over 92% nationwide), but it remains a danger to the unvaccinated, and its return could imperil the global effort to eradicate polio as a human disease.