If the pattern from recent history holds, starting next month, doctors in the U.S. will begin seeing a spike in cases of a polio-like condition in children that leaves them with muscle weakness, paralysis, and, in the most severe cases, trouble breathing.
But 2020, if you haven’t noticed, is not your average year.
Now, experts are waiting to see what will happen this go-around with the condition, called acute flaccid myelitis, or AFM. They’ve witnessed bursts of cases in the late summer and fall of 2014, 2016, and 2018, but they’re wondering if AFM, which is thought to be a rare result of a common viral infection, might be influenced by all the distancing measures put in place to slow the coronavirus pandemic.
That is, efforts to cut down on the spread of the coronavirus might have the same effect on the virus believed to lead to AFM.
“That’s an idea that very well may play out,” said Matthew Vogt, a pediatric infectious disease specialist at University of North Carolina at Chapel Hill. “And all of us who pay attention to AFM are watching that.”
It’s not clear that will happen, and experts are urging clinicians to be on the lookout for children with muscle weakness or slow reflexes. AFM progresses quickly once symptoms start, and getting children to specialists quickly can improve outcomes. And as people have started emerging from shelter-at-home policies in the past few months, it’s possible that the virus that thought to lead to AFM, EV-D68, is rebounding, just as circulation of SARS-CoV-2, which causes Covid-19, has resurged.
“I’m uncertain what kind of impact social distancing practices are going to have on EV-D68,” said Megan Culler Freeman, a pediatric infectious disease specialist at Children’s Hospital of Pittsburgh.
EV-D68 is a respiratory virus and, as recent research has found, the primary suspect behind the bulk of AFM cases. (Other viruses, including EV-A71, are thought to cause AFM as well.) It’s part of the enterovirus family (hence the EV) and, for most people, causes only colds or asthma-like symptoms.
But in 2014, doctors noticed a surge of polio-like illnesses in children, a pattern that has repeated every two years since. Since the Centers for Disease Control and Prevention started tracking AFM in 2014, there have been 630 confirmed cases. (Doctors have since looked at earlier years and retrospectively identified AFM cases, and there are a small number of cases in off years as well. The increasing numbers could be a result of both AFM becoming more common for some reason and of better detection and reporting practices.)
Scientists have traced the potential cause to EV-D68, finding evidence of an immune response to the virus in patients’ spinal fluid. But it’s still not clear whether the damage to nerves in the spinal cord that leads to the movement problems is caused by the virus itself, an aberrant immune response to the viral infection, or some combination of the two.
Freeman said she leaned toward the immune system as the culprit. Kids who develop AFM typically do so about a week after experiencing cold symptoms, which means it’s “probably driven by the person, not a difference in the virus.”
But researchers are not sure why such a small number of children develop AFM — perhaps fewer than 1% of those infected — given how widely EV-D68 circulates during its season. Researchers are looking into patients’ genes and their health histories for clues.
“We don’t have a strong handle on why the kids who get AFM, why are they the unfortunate ones?” Vogt said.
The every-other-year AFM clusters correspond to the levels of circulating EV-D68, which remain low during the off periods and then rise ahead of the spike in AFM cases. It’s possible that people infected by the virus one year develop some protection that lasts long enough to prevent a surge the next year — like a short-term form of herd immunity — but not long enough to stave off another surge in two years.
It’s still too early to know whether EV-D68 levels are going to increase this year as they have in past even-numbered years, and if the physical distancing policies Americans have been embracing to various extents since March will have an effect. Surveillance data indicate that enterovirus levels collapsed in March as shelter-at-home policies went into effect, though not as much as those of other viruses, such as influenza. Enteroviruses also seemed to pick up more quickly than other viruses in June and July as states lifted their lockdown restrictions.
AFM shares some similarities to another condition researchers have started seeing in some children with Covid-19. Called multisystem inflammatory syndrome in children, or MIS-C, it involves severe inflammation affecting multiple organ systems and typically appears two to four weeks after a Covid-19 case. (It’s also a rare consequence of Covid-19; children generally have mild cases compared to adults, particularly the elderly.) Both AFM and MIS-C could be the result of an overactive immune system persisting after an acute viral infection, and both seem largely limited to children. But there are key differences: While AFM, for example, involves the nervous system, MIS-C largely affects the heart and blood vessels.
“The idea that they both could be aberrant immune responses to otherwise common viruses, that’s a possibility,” Vogt said.