(CNN) -- "About 20" cases of a polio-like syndrome have been identified in California children over the past 18 months, a Stanford University researcher says. Dr. Keith Van Haren, a pediatric neurologist at Lucile Packard Children's Hospital Stanford, has written a report about five of the early cases. In that report, which will be presented in April at the American Academy of Neurology's annual meeting, neurologists said they had identified five patients who developed paralysis in one or more of their limbs between August 2012 and July 2013. All five children had been vaccinated against the poliovirus. Treatment did not seem to help the children regain their motor function.
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Neurologist: Cases don't seem to be "a major epidemic but only a very rare phenomenon"
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Some children tested positive for enterovirus 68, a rare virus linked to respiratory illness
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Another type, enterovirus 71, is more commonly linked to paralysis
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Both are uncommon in the United States; health officials say risk is low
More common -- and more concerning to health officials -- is enterovirus 71, which was discovered by the same @placeholder lab in 1969, Oberste said.