Frequently Asked Questions

What can I do if I suspect AFM?

  • Seek medical care immediately if you or your child develops any of these symptoms: weakness or loss of muscle tone or reflexes in the arms or legs, facial droop or weakness, difficulty moving the eyes, drooping eyelids, difficulty with swallowing, or slurred speech.
  • If your clinician suspects you or your child has AFM, they should hospitalize immediately. AFM can progress rapidly and sometimes require machines to help patients breathe.

Possible Causes

Why does CDC believe that viruses play a role in AFM?

  • CDC has been tracking AFM since 2014, and our five years of surveillance data have contributed important evidence to support a role for viruses, including enteroviruses, in AFM. For example,
    • We’ve seen a seasonal pattern to AFM. Most patients develop AFM in late summer or early fall. At this same time of year, many viruses, including enteroviruses, commonly circulate in the U.S.
    • Most patients had respiratory symptoms or fever consistent with a viral infection less than a week before onset of limb weakness.
  • Our sustained work will help lead to more answers about this complex illness, such as why some people develop AFM, and why outbreaks are occurring.

Recent research has indicated that enteroviruses are the likely cause of AFM. Does CDC believe this as well?

  • CDC believes that viruses, including enteroviruses, play a role in AFM. While we often find evidence of enterovirus respiratory illness in patients with AFM, we rarely have confirmed enteroviruses in spinal fluid.
  • Recently, cutting edge technology has demonstrated the presence of enterovirus antibodies in the spinal fluid of patients with AFM. This evidence is an important first step toward understanding how AFM develops, and why only some children are severely affected.
  • CDC’s partnerships with other institutions, such as universities, federal agencies, and health departments, are important to better understand AFM and these outbreaks.

How is AFM different from polio?

  • Poliomyelitis is the term used to describe the syndrome of acute flaccid limb weakness and lesions in the grey matter of the spinal cord. Poliomyelitis caused by poliovirus no longer occurs in the United States. In 2014, the term AFM was adopted to describe poliomyelitis without a known cause and not caused by poliovirus.
  • We now have stronger evidence that points to AFM being caused by non-polio enteroviruses, such as EV-D68 and EV-A71. Poliovirus can be prevented by a vaccine. However, there is no vaccine yet available for EV-A71 in the United States, and no vaccine for EV-D68 or for the other enteroviruses that are believed to cause AFM.
  • All the stool specimens from AFM patients that we received tested negative for poliovirus. We continue to test all specimens from AFM patients to look for viruses, including poliovirus and non-polio enteroviruses.

Is there an immune response that could trigger AFM?

  • CDC does not know why some people develop AFM. We are investigating whether a virus might cause indirect damage to a patient’s body by triggering their immune response, which then attacks motor neurons in the spinal cord (nerves that make the muscles move).
  • It is likely that a virus causes direct damage to the motor neurons, and it is possible that host genetic factors cause certain patients to be more susceptible than others.

Is there a link between vaccinations and AFM?

  • CDC does not have evidence to suggest that vaccinations play a role in AFM.
  • Of the AFM cases reviewed in 2018, approximately 85% had no recorded vaccinations in the 30 days prior to the onset of limb weakness.
  • We continue to review past medical history of all cases, including past vaccinations, as part of our investigation.
    • In 2018, AFM occurred in children who had received vaccines, and also in children who had received no vaccines. CDC will conduct further analyses using data abstracted from medical charts and vaccination histories to examine whether vaccines could be related to AFM.
    • In a 2016 study of 10 confirmed cases of AFM in children, 9 had received all childhood vaccines recommended by the Advisory Council on Immunization Practices. When vaccine records were examined, the average amount of time between when they got their last vaccine and when they started to experience AFM symptoms (i.e., limb weakness), was almost 2 years.

Health Outcomes

Has anyone died from AFM?

  • Two patients with confirmed AFM died in the acute phase of their illness, one in 2017 and one in 2020. We have also learned of deaths in cases confirmed in previous years.
  • CDC is gathering information on deaths reported to us from health departments. We are also gathering information as part of our patient outcome data collection. We ask that health departments send information about every death of an AFM case to CDC.

When will CDC or state health departments follow up with all patients?

  • CDC has implemented a systematic process for determining the patients’ outcomes at 2, 6, and 12 months after limb weakness began.
  • We are currently interviewing confirmed and probable cases from 2018 and will be interviewing these cases in subsequent years moving forward.


Why is there an increase in AFM cases every two years?

  • CDC has observed that the increases in AFM cases since 2014 have coincided with increases in enterovirus circulation, and in 2014, with a national outbreak of respiratory illness caused by EV-D68. A mix of enteroviruses circulates every year, and different types of enteroviruses can be common in different years, so this may contribute to the AFM increases every two years.
  • We continue to actively investigate the causes of AFM increases.

How are AFM cases reported to CDC?

All health departments have some type of requirement for clinicians to report suspected AFM cases. Here are the steps to reporting:

  1. The health department works with healthcare providers to collect medical information and spinal cord MRI images.
  2. The health department then sends this information to CDC.
  3. Once we receive a report from the health department, the patient summary form and spinal cord images are reviewed by neurology experts for a final case classification.
  4. Once we’ve made a final case classification, we send that information to the health department to then share with the clinician, and the clinician shares it with the patient and their family. Clinicians should not wait for CDC’s case classification for diagnosis.

Due to confidentiality reasons, CDC does not have access to patient information such as names, so we are not able to tell whether a specific patient’s records have been sent to us. We strongly encourage you to reach out to your state health department if you have questions about whether your child has been reported to CDC. CDC does not decide which diseases are nationally notifiable, but we do advise the Council of State and Territorial Epidemiologistsexternal icon and make recommendations about which diseases should be nationally notifiable.

How do we know every case of AFM is being recognized?

  • All jurisdictions have some type of requirement for clinicians to report patients under investigation (PUIs) for AFM, either by making AFM reportable, having provisions for reporting suspicion of acute onset of flaccid paralysis without other apparent cause, or having provisions that require reporting of new or emerging conditions of public health importance, like AFM.
  • In June 2019, it was proposed that AFM be made nationally notifiable at the Council of State and Territorial Epidemiologists (CSTE) annual meeting. The proposal did not pass.
  • State and local health departments, CSTE, and CDC, will continue to collaborate and respond to AFM.

Why is CDC’s case definition not counting all patients with AFM?

  • CDC has case definitions for AFM with specific criteria that we use to classify patients as having a confirmed or probable case of this illness. If a patient does not meet these criteria, they are classified as “not a case” of AFM.
    • By focusing on the confirmed cases, it helps us make sure we are focusing only on patients with the most similar symptoms. We can then compare them to one another to get a better sense of possible risk factors and causes of AFM. This can help to give us a better understanding of the disease.
  • A case classification by CDC is not meant to override a clinician’s diagnosis of a patient’s illness, or his or her treatment and rehabilitation plan.
  • Even though some patients may not meet our case definitions, the information provided about these patients still helps us understand the full spectrum of illness.
  • As we continue to learn more about AFM and its initial symptoms, we are working with our partners to refine our case definition so that we can better understand this disease and what causes it.