Children who received the measles-mumps-rubella (MMR) vaccine did not have a higher risk of developing autism than children who did not receive the vaccine, according to a study published Monday in the Annals of Internal Medicine.

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The study comes as the United States grapples with measles outbreaks throughout the country, and adds to the body of evidence debunking unfounded claims that there is an association between receiving the MMR vaccine and developing autism, Reuters reports.

Background: Research shows no link between vaccines, autism

The idea that vaccines are linked with autism largely stems from a study published in The Lancet in 1998 that was retracted in 2010. The study's author later had his medical license revoked based on alleged ethical violations and his failure to disclose conflicts of interest.

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Since then, research has shown there is no link between vaccines and autism. CDC on its website states, "Many studies … have looked at whether there is a relationship between vaccines and autism spectrum disorder [ASD]," and, "[t]o date, the studies continue to show that vaccines are not associated with ASD."

Two American Academy of Pediatricians physicians in 2017 wrote, "Claims that vaccines are linked to autism, or are unsafe when administered according to the recommended schedule, have been disproven by a robust body of medical literature." They continued, "Delaying vaccines only leaves a child at risk of disease."

Study details

For the new study, which was conducted as a follow up to a similar study published in 2002, researchers from Copenhagen's Staten Serum Institute in Denmark analyzed data on 657,461 children born between 1999 and 2010 to examine the association between MMR vaccines and autism. According to the researchers, 95% of the children included in the study received MMR vaccinations.

The researchers followed up with the children from the time the children were age one through August 2013. The researchers linked information they found in public registries regarding the children's vaccination status to information on the children's autism risk factors, such as sibling history of autism, and autism diagnoses among the children.

The researchers noted the study had some limitations, including the potential for children to have had undiagnosed autism before receiving their MMR vaccinations, which could appear to link autism to the MMR vaccine when there is no such connection. The researchers also noted the potential for parents to forgo having their children receive the MMR vaccination at the onset of autism symptoms. Further, the researchers did not design the study to determine whether or how vaccines might cause autism, Reuters reports.

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Findings

Overall, the researchers found 6,517 of the 657,461 children included in the study had been diagnosed with autism during the follow-up period. The researchers found the children who received the MMR vaccination were 7% less likely to develop autism when compared with children who did not receive the vaccination. In addition, the researchers found children who received no childhood vaccinations were 17% more likely to be diagnosed with autism when compared with children who received their recommended vaccinations.

The researchers also found MMR vaccination was not associated with an increase in children's risks of developing autism if they had siblings with ASD. However, the researchers found children who had siblings with ASD were more than seven times more likely to be diagnosed with autism than children who did not have siblings with ASD.

In addition, the researchers found boys were four times more likely than girls to be diagnosed with autism.

The researchers concluded that the study's "results offer reassurance and provide reliable data" to "suppor[t] that MMR vaccination does not increase the risk for autism."

Comments

Anders Hviid, one of the study's authors from the Staten Serum Institute, said, "The idea that vaccines cause autism is still around despite our original and other well-conducted studies." Hviid said he and his colleagues "felt that it was time to revisit the link in a larger cohort with more follow-up which also allowed for more comprehensive analyses of different claims, such as the idea that MMR causes autism in susceptible children."

Saad Omer and Inci Yildirim of Emory University in an editorial accompanying the research wrote the new study, along with others like it, can help physicians refute claims that MMR vaccines are linked with autism. Omer in an email to NPR's "Shots" wrote, "Physicians should do what they do best" and "follow the emerging evidence—including that in vaccine communication science—and use it in their interactions with their patients and as public health advocates" (Stein, "Shots," NPR, 3/4; Monaco, MedPage Today, 3/4; Rapaport, Reuters, 3/4; Hellmann, The Hill, 3/4; Stanley-Becker, "Morning Mix," Washington Post, 3/5).

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