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The measles, mumps and rubella (MMR) vaccine isn't associated with an increased risk of autism, even among kids who are at high risk because they have a sibling with the disorder, a Danish study suggests.
Concerns about a potential link between the MMR vaccine and autism have persisted for two decades, since a controversial and ultimately retracted 1998 paper claimed there was a direct connection. Even though subsequent studies haven't tied inoculation to autism, fear about the risk has weighed on parents so much in several communities across Europe and the U.S. that vaccination rates have been too low to prevent a spate of measles outbreaks.
In the current study, researchers examined data on 657,461 children. During this time, 6,517 kids were diagnosed with autism.
Kids who got the MMR vaccine were seven percent less likely to develop autism than children who didn't get vaccinated, researchers report in the Annals of Internal Medicine.
"Parents should not skip the vaccine out of fear for autism," said lead study author Dr. Anders Hviid of the Statens Serum Institut in Copenhagen, Denmark.
"The dangers of not vaccinating includes a resurgence in measles which we are seeing signs of today in the form of outbreaks," Hviid said by email.
Measles is a highly contagious virus that can be fatal. It starts with a fever that can last a couple of days, followed by a cough, runny nose and pink eye. A rash develops on the face and neck and then spreads to the rest of the body. In severe cases, pneumonia and encephalitis, an inflammation of the brain, can develop.
People with measles can spread the virus for several days before and after the rash appears.
The virus can live for up to two hours on surfaces where an infected person coughs or sneezes. People can become infected by breathing in droplets or touching a contaminated surface and then touching their eyes, nose or mouth.
Just a five percent reduction in vaccination coverage can triple measles cases in the community, researchers note.
Researchers studied the connection between the MMR vaccine and autism in a nationwide cohort of all children born in Denmark to Danish-born mothers from 1999 to 2010. They followed kids from age one through the end of August 2013.
Overall, 95 percent of the kids in the study got the vaccine.
Children with autistic siblings were more than seven times more likely to be diagnosed with autism than kids without this family history, the study found.
Boys were four times more likely to be diagnosed with autism than girls, the study found.
And, children who had no childhood vaccinations were 17 percent more likely to be diagnosed with autism than kids who did get recommended vaccinations.
Early symptoms of autism can vary but may include repetitive behaviors like hand flapping or body rocking, extreme resistance to changes in routine, and sometimes aggression or self-injury. Behavioral, educational, speech and language therapy may help reduce the severity of autism symptoms in some children.
The study wasn't a controlled experiment designed to prove whether or how vaccines might cause autism.
Another drawback is the potential for some kids to have undiagnosed autism before getting the MMR vaccine, which could make the MMR vaccine appear linked to autism when it really isn't connected, the study authors note. It's also possible that the onset of autism symptoms might lead parents to skip the vaccine.
Still, the study adds to a large body of evidence showing that vaccines don't cause autism, writes Dr. Saad Omer of Emory University in Atlanta, co-author of an accompanying editorial.
"Any myth should be clearly labeled as such," Omer writes. "Even in the face of substantial and increasing evidence against an MMR-autism association, the discussion around the potential link has contributed to vaccine hesitancy."