A "polio-like" syndrome has been discovered in five California children, and researchers are now taking a closer look at its cause.
Since August 2012, a handful of children have suffered sudden paralysis in "one or more arms or legs ... [that] was most severe within about two days," according to CBSNews.com.
Researchers and public health officials in the state are now investigating up to 25 cases.
"These five new cases highlight the possibility of an emerging infectious polio-like syndrome in California," Keith Van Haren, M.D., of Stanford University in Palo Alto, Calif., said in a statement on Sunday.
Van Haren added, however, that these symptoms are not the result of the polio virus, a contagious virus that also causes limb paralysis.
"Although poliovirus has been eradicated from most of the globe, other viruses can also injure the spine, leading to a polio-like syndrome," Van Haren said in the statement.
All five of the children had been vaccinated against poliovirus.
And while Van Haren stressed that this is a very rare condition, "Any time a parent sees symptoms of paralysis in a child, the child should be seen by a doctor right away."