The myth that autism is linked to childhood vaccines first appeared in a 1998 study by British physician Dr. Andrew Wakefield. The study was later retracted, and Wakefield was discredited. But nearly three decades after the study’s publication, the myth persists, championed by activists, political leaders, and even potential health officials. 

There is overwhelming evidence that there is no link between vaccines and autism. “No one has any real or solid evidence that vaccines cause autism,” says Catherine Lord, a psychologist and autism researcher at the University of California, Los Angeles. 

Here are just some of the many reasons that we know vaccines don’t cause autism.

The Wakefield study has been thoroughly discredited 

In 1998, the Lancet published a study describing a small group of children who reportedly had bowel inflammation and developed autism within a month of getting the measles, mumps, and rubella (MMR) vaccine. The study proposed that the vaccination triggered bowel inflammation and developmental delays, including autism. Lead author Andrew Wakefield coined the term “autistic enterocolitis” to describe the condition he and his colleagues claimed to have discovered. 

The study received significant media attention and immediate criticism from scientists, who pointed out the study’s small size, lack of controls, and insufficient evidence to support its conclusions. 

Subsequent research published over the next few years refuted Wakefield’s findings. A 1999 Lancet study found no link between autism and the MMR vaccine, and a 2001 study found no evidence of a link or the existence of so-called autistic enterocolitis.

In 2010, the Lancet finally retracted Wakefield’s fraudulent study, noting that “several elements” of the study were “incorrect” and that the experiments carried out on children had not been approved by an ethics board. The journal’s editor called the paper’s conclusions “utterly false.” 

A few months later, Wakefield was stripped of his medical license by the United Kingdom’s General Medical Council. The council deemed Wakefield “dishonest and irresponsible” and concluded that he conducted unethical experiments on children. 

The committee’s investigation also revealed that, less than a year before he published his study claiming that the MMR vaccine was linked to bowel inflammation that triggered autism, Wakefield filed a patent for a standalone measles vaccine and inflammatory bowel disease treatment.

Thimerosal was removed from childhood vaccines in 2001—with no effect on autism rates

A 2003 study published by a conservative group known for promoting anti-science myths—including that HIV doesn’t cause AIDS—first proposed that the preservative thimerosal in childhood vaccines is linked to autism. This supposed link was subsequently disproven.

Thimerosal is added in small amounts to some vaccines to prevent dangerous bacterial and fungal contamination. The substance contains ethylmercury, a form of mercury that the body quickly and safely processes in small doses. 

Ethylmercury is different from methylmercury, a far more dangerous form of mercury that is toxic at low doses. By contrast, the small amount of thimerosal in some vaccines is harmless to humans and is equal to the amount of mercury in a can of tuna. 

The preservative was removed from childhood vaccines as a precautionary measure in 2001. With the exception of some flu shots, no childhood vaccine contains the preservative and hasn’t for more than two decades. Autism rates have not decreased as a result of thimerosal being removed from childhood immunization vaccines. While some types of the annual flu vaccine contain thimerosal, you can get one without it.

Extensive research also shows that neither thimerosal nor methylmercury at any dose is linked to autism. A 2008 study of statewide California data found that autism rates “increased consistently for children born from 1989 through 2003, inclusive of the period when exposure to [thimerosal-containing vaccines] has declined.”

Autism rates are the same in vaccinated and unvaccinated children

Vaccine opponents often falsely claim that vaccinated children are more likely than unvaccinated children to develop autism. Decades of research disprove this false claim. 

A 2002 analysis of every child born in Denmark over eight years found that children who received MMR vaccines were no more likely to be diagnosed with autism than unvaccinated children. 

A 2015 study of over 95,000 U.S. siblings found that MMR vaccination is not associated with increased autism diagnosis. This was true even among the siblings of children with autism, who are seven times more likely to develop autism than children without an autistic sibling.

And a 2018 study found some evidence that children with autism—and their siblings—were more likely to be unvaccinated or under-vaccinated than children without autism.

Vaccination also has no impact on autism rates at the population level, regardless of the age at which children get vaccinated. 

“In comparing countries that have different timing and levels of vaccination … there’s no difference in autism,” says Lord. “You can look at different countries with different rates of autism, and there’s no relationship between the rates of autism and vaccinations.”

Countries such as Taiwan, Tunisia, Turkey, and Morocco, which have some of the world’s lowest autism rates, have childhood immunization rates that are nearly identical to countries with the highest autism rates, including Sweden, Japan, Brunei, and Singapore. 

Improved awareness and diagnosis play a role in rising autism rates

Autism was first described in 1911 when it was considered to be a form of severe schizophrenia. Over a century later, our understanding of autism has changed drastically, as have diagnostic standards. 

A 2013 scientific article describing how medical and social perceptions of autism have evolved explains that “the diagnoses of schizophrenia, psychosis and autism in children were largely interchangeable during the 1940s and 1950s.” Beginning in the 1960s, methods of diagnosing autism improved, “increasing the number of children who were considered to display autistic traits.”

The autism diagnosis was changed to autism spectrum disorder in 2013. “This category is now very broad, which was an intentional choice to help provide services to the greatest number of people who might need them,” writes Gideon Meyerowitz-Katz, an epidemiologist and creator of the popular Health Nerd blog. 

“Rather than the severe intellectual disability of the 1940s and 50s, [autism spectrum disorder] is a group of behaviours that can be any severity as long as they are persistent and impact people’s daily functioning in a significant way.” 

For more information about autism, talk to your health care provider.

This article first appeared on Public Good News and is republished here under a Creative Commons license.