By Dr. Jeff Duchin, Health Officer
Recent cases of acute flaccid myelitis (AFM) locally and across the US have parents, health care providers and public health professionals deeply concerned and looking hard for the cause, which remains unknown. Based on what we do know about causes of AFM, the leading suspect is infection with a virus because several viruses are known to cause AFM in a very small number of people who become infected.
Some have expressed the opinion that vaccines may be causing the AFM cases. Like most children in the US, children who develop AFM have usually received recommended childhood vaccines at the appropriate ages. However, there are a number of reasons why health care providers and public health professionals say childhood vaccines are not likely to be the cause of the current increase in AFM cases:
- AFM cases are seen at a variety of ages and not at an age when a particular childhood vaccine is regularly given. The average age of AFM cases in the largest published reports from the US is 7 and 9 years, and the age of reported AFM cases ranges from 6 months to 21 years and older. So, the ages of AFM cases vary and are past the time when most childhood vaccines are routinely given.
- Current childhood vaccines are not associated with AFM, and the same vaccines have been used for many years prior to the increase in AFM cases. There have been no changes in the vaccines in recent years, including when the increase in AFM was noted in 2014.
- Previously, AFM was a rare complication of the oral polio vaccine used in the US before 2000. That vaccine used a live, weakened polio virus. After 2000, only the inactivated polio vaccine (no live virus) has been in used in the US, and it does not cause AFM. Also, since that time, AFM has not been reported through ongoing vaccine safety monitoring in the US.
- The 2014 increase in AFM cases was temporally associated with an outbreak of a virus (EV-D68) that is related to other similar viruses known to cause AFM. However, whether EV-D68 has a role in AFM cases remains unproven and the investigation to determine the cause of recent AFM cases is ongoing.
- There have been many studies of vaccine safety. None of the vaccines currently used in the United States are known to cause AFM. However, in the rare instance that AFM does occur, it is usually after infection with certain viruses. Most children (over 70%) with AFM have reported symptoms of a viral respiratory or GI infection preceding the onset of AFM.
- And finally, childhood vaccinations are given every month of the year based on when children are born and their ages, but AFM has occurred seasonally, peaking in late summer or fall, when certain viruses associated with AFM are also circulating.
In summary, available evidence does not support the claim that vaccines are related to AFM. Ongoing, intensive investigation into the cause and mechanism of AFM will remain a priority for public health and medical professionals. As more information becomes available, you can find updates here.