This may be a horrible year for a polio-like disease caused by a common virus

 Students listen to their teacher during their first day of transitional kindergarten at Tustin Ranch Elementary School in Tustin, Calif., on Wednesday, August 11, 2021.
Enlarge / Students listen to their teacher during their first day of transitional kindergarten at Tustin Ranch Elementary School in Tustin, Calif., on Wednesday, August 11, 2021.

The Centers for Disease Control and Prevention is warning that a common respiratory virus in children is surging in several regions of the US, raising concern that an unusually large and alarming spike in a polio-like condition could soon follow.

The virus—a non-polio enterovirus called EV-D68—typically causes mild respiratory illness, much like a cold, and is often an indistinguishable drip in the constant stream of snotty childhood illnesses. But in recent years, experts have pinned EV-D68 to a rare but serious polio-like neurological condition called acute flaccid myelitis (AFM). In a small number of children (median age of 5 years), the condition trails an EV-D68 illness by around a week, causing muscle and limb weakness that can lead to long-term or even permanent paralysis.

In 2014, a surge in EV-D68 cases raised the virus’ profile despite being identified in 1962. Since then, the CDC has recorded closely linked spikes of EV-D68 and AFM cases that follow a two-year pattern, landing in late summer and fall. Why every other year? While EV-D68 circulates continuously at low levels, epidemiological modeling suggests that two years is how long it takes for a large enough pool of susceptible children to build up and EV-D68 transmission to take off. (Adults are generally unfazed by the virus, following wave after wave of exposure to non-polio enteroviruses during childhood.)

After paired peaks in 2014 and 2016, the largest rise came in 2018, when annual AFM reached a record 238 documented cases nationwide following a surge in EV-D68 activity. Experts had braced themselves for yet another bad year in 2020. But then the COVID-19 pandemic hit.

Offbeat outbreaks

In March 2020, well before EV-D68’s expected heyday, daycares closed, schools went virtual, and social gatherings were canceled. People donned masks, improved ventilation, and impulsively sanitized their hands. The deadly pandemic upended people’s lives worldwide—and knocked a slew of other infectious diseases out of rhythm.

Most notably, seasonal influenza was nearly non-existent in the fall of 2020. It meekly returned in fall 2021 but had an unusual, offbeat upswing in spring 2022. Experts fear it could come roaring back this fall and are encouraging flu vaccines. Meanwhile, the cadence of another common childhood respiratory infection, respiratory syncytial virus (RSV), also swung unexpectedly; the CDC issued an alert in June 2021 that the cold-season virus was thriving in the summer.

Then there’s EV-D68. The CDC tracks the activity of EV-D68 through a surveillance system of acute respiratory illnesses (ARI) documented at seven sentinel health care sites around the country. Between July and November 2017—an EV-D68 off year—about 0.08 percent of documented ARIs were linked to EV-D68. In 2018, a peak year, the percentage rose to 11 percent, then fell to 0.2 percent in 2019. Epidemiologists expected another high year in 2020, but amid the pandemic, EV-D68 ARIs that year rose to just 1.4 percent. And 2021 was also low at 0.3 percent. That’s according to unpublished data presented by CDC epidemiologist Claire Midgley at the CDC’s International Conference on Emerging Infectious Diseases (ICEID) in early August.

AFM cases by year.
Enlarge / AFM cases by year.

The viral wobbling is particularly concerning for EV-D68 and AFM. With its two-year cycle thought to be dependent on amassing enough susceptible children, a four-year gap suggests the virus could mushroom. At last month’s meeting, Midgley presented early data hinting at such a scenario. In “very, very preliminary data,” Midgley said the CDC saw 71 EV-D68 detections among about 3,500 ARIs in its surveillance network by July 2022. “That’s more than we saw throughout 2019 and 2021 in total,” she said. “So this is something we’re keeping an eye on. There’s potential for more circulation this year.” The CDC has not yet seen a corresponding increase in confirmed AFM cases, she added last month, but it’s “something we’re monitoring and preparing for potentially over the next few months.”

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