MMR Vaccine Prevents Autism—By Preventing Congenital Rubella

Scope Correspondent

In 1998, Andrew Wakefield published a study in The Lancet that has since been repeatedly and widely discredited, claiming that the measles-mumps-rubella (MMR) vaccine might cause autism. No such thing is true. It later came to light that Wakefield had violated ethics in many ways and deliberately lied about the results, and The Lancet retracted the paper in 2010.

Unfortunately, much damage was already done, as thousands of parents had decided not to vaccinate their children. In recent years, measles epidemics have been making a comeback, especially in Europe, where the MMR autism scare was greatest. In 2011 alone, measles outbreaks in Europe sickened 26,000 people and killed nine.

The irony of all this is that the MMR vaccine has been preventing autism all along, by protecting pregnant women from rubella.

Image by Sanofi Pasteur. Used under Creative Commons license.

The rubella virus

Rubella—the virus putting the R in the MMR vaccine since 1971, when the combined vaccine was licensed—is not generally a fatal or even severe disease. Like the common cold, it is transmitted by airborne droplets. Patients can be contagious for a week before showing symptoms. In children, rubella can cause a fever, sore throat, and a rash of pink spots that spread from the face across the body. In adults, it may also cause headaches, pinkeye, and arthritis.

But the greatest danger is if a pregnant woman contracts rubella, especially during her first trimester. Rubella can cause congenital rubella syndrome (CRS) in the fetus. CRS is characterized by permanent birth defects, including hearing loss, cataracts, heart abnormalities, diabetes, liver damage, and autism.

A study led by Bryn Berger at Emory University estimated that, between 2001 and 2010 in the US alone, rubella vaccination prevented about 1200 cases of autism spectrum disorder. The study was published in the journal BMC Public Health in 2011.

Based on research in Jamaica and mathematical modeling in Norway and Australia, the researchers conservatively estimated that the incidence of CRS in the US without the rubella vaccination would be about 4 per 10,000 births. Taking that number and multiplying it by the number of births in the US from 2001 to 2010, they estimated that 16,600 cases of congenital rubella syndrome were prevented by rubella vaccination in the US just those 10 years.

Berger and his colleagues then used a 1971 study by Stella Chess that looked at 243 preschool children with CRS. This was just after a worldwide rubella epidemic from about 1963 to 1965—the US alone saw 12.5 million cases of rubella, about 11,000 babies who died after contracting the disease, and 20,000 children born with CRS. Chess’s study found that 7.4% of the 243 children with CRS had either full or partial autism.

If the rubella vaccine prevented 16,600 cases of CRS, and roughly 7.4% of those would have had autism, then the vaccine prevented autism in about 1,200 US children over ten years.

The authors of the study point out that by using Chess’s numbers for the percentage of CRS children who have autism, they are actually underestimating the number of autism cases being prevented, because the diagnostic criteria for autism have widened since 1971.

Rubella was declared eliminated in the US in 2004, and in the Americas in 2009, thanks to the rubella vaccine, first developed in 1969 by Maurice Hilleman and later improved into the form we use today by Stanley Plotkin.

But rubella has not yet been eliminated completely. Worldwide, about 100,000 babies are born with CRS each year. Even in the US and other places where rubella has been eliminated, people from areas where rubella still occurs can travel or immigrate here, bringing the virus with them. So women who are thinking of becoming pregnant are advised to get a rubella vaccination four weeks before pregnancy if they haven’t already been vaccinated or developed immunity. Once a woman is pregnant, the rubella vaccination is not recommended until after she gives birth.

Clearly not everyone who becomes pregnant has four weeks of advance warning to get a rubella vaccination. So what happens when all the kids who haven’t gotten the MMR vaccine grow up and begin getting pregnant?