Doctors are looking for more information about a `` polio-like syndrome '' that has caused paralysis in a few children in California . Neurologists have 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 . Samples from two of the children tested positive for enterovirus 68 , a rare virus that has been linked to severe respiratory illness in the past . Samples from the other three children were not collected or tested soon enough to yield conclusive results , said Dr. Emmanuelle Waubant , a neurologist at the University of California , San Francisco . Waubant and her colleagues will present a case report about these patients ' illnesses at the American Academy of Neurology 's annual meeting in late April . They are asking health care providers to be on the lookout for similar cases and send in samples from any patient exhibiting these symptoms . Dr. Carol Glaser , chief of the Encephalitis and Special Investigation Section at the California Department of Public Health , said the state is aware of the paralysis cases but believes the risk to families is very low . `` We are evaluating cases as they are reported to us , '' Glaser said in an e-mail to CNN . `` We have not found anything at this point that raises any public health concerns . '' The poliovirus has been eradicated in the United States for more than 30 years . Only three countries in the world are not yet free of the disease : Afghanistan , Pakistan and Nigeria , according to the World Health Organization . Why polio has n't gone away yet . Poliovirus is part of the Picornaviridae family , which also includes enteroviruses and rhinoviruses ( better known as the common cold ) . There are more than 100 types of enterovirus that cause 10 million to 15 million infections in the United States each year , according to the Centers for Disease Control and Prevention . Most people who become infected with an enterovirus do not get sick or experience only mild symptoms , said Dr. Steven Oberste , chief of the Polio and Picornavirus Laboratory Branch at the CDC . Common symptoms include fever , runny nose , cough , skin rash and body aches . Enterovirus is often the cause of `` summer colds , '' whose cases spike in July , August and September . Children and teens are more likely to fall ill because they have not yet built up immunity to these common viruses . However , some types of enterovirus are more serious . These can cause hand , foot and mouth disease ; viral meningitis ; encephalitis ( inflammation of the brain ) ; an infection of the heart ; and paralysis in some patients . Enterovirus 68 was first identified in a California lab in 1962 , after four children came down with a severe respiratory illness . Between 1970 and 2005 , only 26 cases of enterovirus 68 in the United States were reported to the CDC . Since 2000 , the government agency has kept a closer watch and has seen 47 cases , Oberste said . Outbreaks have occurred over the years in Asia and Europe , but it 's still one of the rarest types of enterovirus . More common -- and more concerning to health officials -- is enterovirus 71 , which was discovered by the same California lab in 1969 , Oberste said . Enterovirus 71 is usually associated with severe neurological issues , including aseptic meningitis , polio-like paralysis and encephalitis . Waubant is not sure if the samples from this latest group of patients were tested for enterovirus 71 . According to a CDC report , several outbreaks of paralysis caused by enterovirus 71 were seen in Europe in the 1960s and 1970s . In the late 1990s and early 2000s , fatal encephalitis was a big problem in Malaysia and Taiwan . `` Ever since then , the virus has circulated in high levels in Southeast Asia , '' Oberste said . In recent years , the outbreaks have spread to Australia ; a cluster of cases near Sydney drew media attention in 2013 . Between 1983 and 2005 , 270 cases of enterovirus 71 were reported in the United States . But none has resulted in a larger outbreak , despite the virus 's infectious nature . `` That 's the really odd thing , '' Oberste said . `` We see cases from time to time in the United States . Occasionally they 'll be severe . Basically it 's identical to what 's circulating in Asia ... but it does n't cause the same big outbreak in disease . And we really do n't know why . '' The CDC is aware of the small cluster of cases in California but is not actively involved in an investigation , a spokesman told CNN . Waubant and her colleagues do n't want to alarm anyone with their case report presentation ; they 're simply seeking help in finding the cause of these seemingly connected cases . `` We would like to stress that this syndrome appears to be very , very rare , '' one of Waubant 's colleagues , Dr. Keith Van Haren , said in a prepared statement . Parents need to know that vaccination is key to preventing polio from returning to the United States , Glaser said . While there is no vaccine to protect you from a non-polio enterovirus , washing your hands frequently and avoiding close contact with others who are sick can help .
Five children in California have a ` ` polio - like disease , '' according to neurologists . One of the children tested positive for virus 68 , a rare type of enterovirus . Another type , virus 71 , is more commonly linked to paralysis . Both are uncommon in the United States ; state health officials say risk is very low .