The Centers for Disease Control and Prevention is warning that a respiratory virus common in children is increasing in several parts of the United States, raising fears that an unusually large and alarming spike in a polio-like illness may soon follow.
The virus – a non-polio enterovirus called EV-D68 – usually causes mild respiratory illness, much like a cold, and is often an indistinguishable drip in the steady stream of snotty childhood illnesses. But in recent years, experts have pinned EV-D68 to a rare but serious polio-like neurological disease called acute flaccid myelitis (AFM). In a small number of children (median age 5 years), the disease follows an EV-D68 illness of about a week, causing weakness in muscles and limbs that can lead to long-term or even permanent paralysis.
In 2014, an increase in EV-D68 cases raised the profile of the virus despite its identification in 1962. Since then, the CDC has recorded closely related spikes in EV-D68 and AFM cases that follow a pattern of two years, landing at the end of the summer and falling. Why every two years? While EV-D68 continuously circulates at low levels, epidemiological modeling suggests that two years is the time it takes for a large enough pool of susceptible children to build up and transmission of EV to occur. -D68 takes off. (Adults are generally unfazed by the virus, after wave after wave of exposure to non-polio enteroviruses during childhood.)
After paired peaks in 2014 and 2016, the biggest increase came in 2018, when the annual AFM reached a record high of 238 documented cases nationwide following an increase in EV-D68 activity. Experts had been bracing for another bad year in 2020. But then the COVID-19 pandemic hit.
In March 2020, long before EV-D68’s expected golden age, daycare centers closed, schools went virtual, and social gatherings were canceled. People wore masks, improved ventilation and impulsively sanitized their hands. The deadly pandemic has upended people’s lives around the world and thrown a host of other infectious diseases out of whack.
Most notably, seasonal flu was almost non-existent in the fall of 2020. It returned slowly in the fall of 2021, but had an unusual and lagged recovery in the spring of 2022. Experts fear it could return this fall and encourage flu shots. Meanwhile, the rate of another common childhood respiratory infection, respiratory syncytial virus (RSV), has also fluctuated unexpectedly; the CDC issued an alert in June 2021 indicating that the cold season virus thrives in the summer.
Then there’s EV-D68. The CDC tracks EV-D68 activity through a documented acute respiratory illness (ARI) surveillance system at seven sentinel healthcare sites across the country. Between July and November 2017, an off-year for EV-D68, approximately 0.08% of documented ARIs were related to EV-D68. In 2018, a peak year, the percentage rose to 11%, then fell to 0.2% in 2019. Epidemiologists expected another high year in 2020, but amid the pandemic, ARI EV- D68 that year rose to just 1.4%. And 2021 was also low, at 0.3%. 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.
Viral oscillation is of particular concern for EV-D68 and AFM. With its two-year cycle thought to depend on collecting enough susceptible children, a four-year gap suggests the virus could be multiplying. At last month’s meeting, Midgley presented the first data hinting at such a scenario. In “very, very preliminary data,” Midgley said the CDC had seen 71 detections of EV-D68 among approximately 3,500 ARIs in its surveillance network by July 2022. “That’s more than what we we’ve seen throughout 2019 and 2021 in total,” she said. “So that’s something we’re watching. There’s potential for more traffic this year.” The CDC has yet to see a corresponding increase in confirmed cases of AFM, she added last month, but it’s “something we’re watching and preparing for potentially over the next few months. “.
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