July 10, 2026 — By Medical Reporting Staff
In the landscape of public health, few conditions are as chilling as Acute Flaccid Myelitis (AFM). Known for its polio-like presentation, this rare but devastating neurological condition causes sudden limb weakness and spinal cord gray matter abnormalities in children. For years, the medical community has operated under a clear working hypothesis: spikes in enterovirus D68 (EV-D68) infections inevitably lead to spikes in AFM.
However, a new report from the Centers for Disease Control and Prevention (CDC), published in the Morbidity and Mortality Weekly Report (MMWR), has introduced a surprising twist in this narrative. Despite significant surges in enterovirus infections across the United States between 2020 and 2025, there has been no corresponding rise in confirmed AFM cases. This disconnect has left researchers questioning the long-standing assumptions about the virus’s neurovirulence and the future of AFM surveillance.
The Core Data: A Shift in the Epidemiological Landscape
The data provided by the CDC offers a detailed look at the status of AFM over the last half-decade. From January 2020 through December 2025, a total of 172 confirmed cases of AFM were reported nationwide. This figure is notably lower than the peaks observed in the mid-2010s, particularly in 2014, 2016, and 2018, when annual case counts reached as high as 238.
The recent numbers are characterized by a relative plateau. In 2025, the CDC recorded just 17 confirmed cases, while the highest annual total in the recent cohort was 48 cases in 2022. This stability stands in stark contrast to the volatile patterns observed during the previous decade, where biennial peaks were the hallmark of AFM epidemiology.
Adriana Lopez, MHS, of the CDC’s National Center for Immunization and Respiratory Diseases, and her colleagues, highlighted that the "expected" correlation between respiratory outbreaks and neurological consequences simply failed to materialize in the recent cycles.
A Chronology of the Disconnect
To understand the mystery, one must look at the timeline of respiratory illness in the U.S. population.
- 2018: A clear, documented seasonal spike in EV-D68 infections correlated perfectly with a surge in AFM cases, reinforcing the theory that the virus was the primary driver of the neurological condition.
- 2020–2021: The onset of the COVID-19 pandemic significantly altered human contact patterns, leading to shifts in the circulation of common respiratory viruses. During this period, AFM case numbers remained low.
- 2022: As society returned to pre-pandemic activities, public health officials raised alarms regarding a resurgence of EV-D68. However, while the respiratory cases surged, the anticipated "AFM wave" did not follow.
- 2024–2025: These years mirrored the 2022 experience. Despite clear surges in enterovirus detections—including EV-D68—the incidence of AFM remained remarkably low. Notably, in 2025, only a single AFM patient tested positive for EV-D68 in a respiratory specimen.
This lack of parity has forced investigators to look beyond the mere presence of the virus and consider the biological nature of the strains currently in circulation.
Supporting Data: Examining the Patient Demographic
The CDC report provides a granular breakdown of the 172 patients affected between 2020 and 2025. The demographic profile of these patients remains consistent with historical data:
- Age Distribution: Approximately 75% of confirmed cases involved individuals under the age of 18. The median age of patients fluctuated between 7 years in 2022 and 12 years in 2023.
- Clinical Presentation: While respiratory illness or fever preceded the neurological onset, the frequency of these symptoms varied significantly by year. In 2022, 2024, and 2025, between 72% and 79% of patients reported prior respiratory symptoms. In contrast, between 2020 and 2023, that number dropped to between 42% and 62%.
- Hospitalization and Mortality: The severity of the condition remains high, with nearly all patients (98% to 100%) requiring hospitalization. Encouragingly, no deaths were reported among this group during the five-year study period.
- Viral Detection: Among the 172 cases, between 26% and 55% tested positive for some form of enterovirus or rhinovirus. The volatility of this percentage—ranging widely from year to year—further complicates the search for a direct causal link.
Why the Disconnect? Scientific Hypotheses
The central question remains: Why does the virus appear to be losing its "bite"?
The authors of the report propose several hypotheses, with the most compelling involving the genetic evolution of EV-D68. Recent laboratory research conducted in mouse models suggests that the predominant strains of EV-D68 circulating in 2022, 2024, and 2025 may lack specific proteins tied to neurovirulence. In essence, the virus may still be infecting children at high rates, but the strains currently in circulation may no longer have the capacity to cross the blood-brain barrier or cause damage to the spinal cord’s gray matter.
However, this is not a guarantee of future safety. Viruses are known for their ability to undergo rapid mutations. A minor shift in the viral genome could potentially restore neurovirulent characteristics, making continued genomic surveillance essential.
Official Responses and Clinical Vigilance
Despite the recent downward trend in AFM cases, the CDC is not lowering its guard. Adriana Lopez and her colleagues emphasize that clinicians must remain hyper-vigilant. AFM is clinically and radiologically indistinguishable from polio—a disease that the world has worked for decades to eradicate.
"Given the unexpected EV-D68 increase in 2025, clinicians should remain alert for patients suspected of having AFM and report these cases to their local or state health department," the report urges.
The Role of Polio Vaccination
The CDC emphasizes that maintaining high polio vaccination coverage is a dual-purpose public health strategy. Not only does it protect against poliovirus, but it also serves as a critical baseline for distinguishing between polio and AFM.
The report notes a concerning gap in surveillance protocols: only about half of the patients with confirmed AFM had stool specimens collected and tested for poliovirus. This falls well below the 80% threshold recommended by global health authorities. Collecting these specimens is the only definitive way to rule out polio and ensure that the U.S. maintains its polio-free status.
Interestingly, 75% to 100% of the confirmed AFM patients in this study had received at least three doses of the polio vaccine, suggesting that the condition is not a result of waning polio immunity but rather a distinct, independent pathogen-driven event.
Implications for the Future
The findings present a complex challenge for public health policy. On one hand, the lack of an AFM surge is a positive development for pediatric health. On the other, the unpredictable nature of viral outbreaks means that the "quiet" years of 2024 and 2025 could be deceptive.
1. The Need for Enhanced Surveillance
Passive reporting, which currently serves as the backbone for AFM tracking, may lead to underestimations of case numbers. The CDC suggests that more active, robust surveillance—particularly in pediatric urgent care and emergency departments—is necessary to capture cases that might otherwise go unreported or misdiagnosed as other neurological issues.
2. Genetic Sequencing
The observation that current EV-D68 strains may be less neurovirulent highlights the critical importance of viral sequencing. Moving forward, public health labs must prioritize sequencing enterovirus samples to track mutations that could lead to the emergence of more dangerous variants.
3. Public Awareness
Parents and healthcare providers should remain aware of the symptoms of AFM: sudden weakness in one or more limbs, drooping of the eyelids or face, and difficulty swallowing or speaking. While the risk of AFM remains statistically rare, the speed of its onset requires immediate medical intervention.
4. Refining Diagnostic Protocols
The failure to reach the 80% threshold for stool sample collection is a critical gap that must be closed. Medical centers must streamline the process of obtaining these specimens from suspected AFM patients, ensuring that public health departments have the data required to differentiate between sporadic AFM and potential re-emergence of poliovirus.
Conclusion
The recent data from the CDC provides a glimmer of hope, suggesting that the most recent respiratory virus spikes have not translated into a neurological health crisis. However, the report serves as a somber reminder that in the world of infectious disease, absence of evidence is not evidence of absence.
As we look toward the future, the medical community must balance the comfort of recent low numbers with the reality that viruses are dynamic, evolving entities. Through continued vigilance, rigorous specimen collection, and ongoing genetic monitoring, the U.S. can ensure that it remains prepared for whatever evolutionary turn the enterovirus family takes next. For now, the "polio-like" mystery continues, reminding us that even in the absence of a surge, the threat of neurological infection remains a shadow on the horizon that requires constant, watchful eyes.
