Autism and vaccination. Numerous studies have looked at a total of over a million children and concluded that there’s no link between autism and thimerosal or vaccination. It’s important to have your child vaccinated to keep them healthy and to prevent outbreaks and reemergence of diseases that vaccines have been able to control.
IN THIS ARTICLE
- Is there a link between the MMR vaccine and autism?
- I’ve heard that a preservative in some vaccines can cause autism – what’s going on?
- Why was thimerosal added to vaccines in the first place?
- Is it true that thimerosal contains mercury?
- Is it true that children were exposed to unsafe levels of mercury from thimerosal?
- How can I tell if my child received vaccines that contained thimerosal?
- Isn’t thimerosal still used in flu shots and some others?
- What are the risks of not immunizing my child?
- Where can I get more information on vaccine safety?
Is there a link between the MMR vaccine and autism?
No. Multiple studies of millions of children over the past two decades have found no link between the MMR vaccine and autism.
The largest, most compelling of these is a study published in the March 2019 issue of the Annals of Internal Medicine. The researchers looked at more than half a million children over the course of ten years. Nearly 32,000 of those kids did not get the MMR vaccine. About 6,500 children were eventually diagnosed with autism. There was no difference in autism rates between the vaccinated and unvaccinated children.
The myth that there’s a connection between autism and the MMR vaccine began with a small study of 12 children published in 1998 and retracted because it was fraudulent.
I’ve heard that a preservative in some vaccines can cause autism – what’s going on?
Some anti-vaccine groups argued that thimerosal, a preservative that was widely use in vaccines, is toxic to the central nervous system and responsible for a rise in rates of autism among children in the United States and around the world.
Over the last 25 years, a number of major medical institutions have reviewed the evidence from the United States and abroad, and all have concluded that there’s no link between autism and exposure to thimerosal. What’s more, the preservative has been removed from childhood vaccines in the United States.
Why was thimerosal added to vaccines in the first place?
Thimerosal was used for over 70 years as a preservative to inhibit the growth of bacteria and fungi in vaccines. Many vaccines are stored most efficiently in large multi-dose vials from which health workers draw individual doses, leaving the vaccine vulnerable to contamination every time the rubber top is punctured by a new syringe. Several deadly incidents of contaminated vaccines in the 1920s prompted vaccine manufacturers to begin adding preservatives to all multi-dose vials of vaccines.
Thimerosal used to be one of the most widely used preservatives. Now that most vaccines in the U.S. no longer contain thimerosal, they are stored in individual dose vials or pre-filled syringes.
Is it true that thimerosal contains mercury?
Yes, thimerosal contains a mercury compound known as ethyl mercury. This is not the same as methyl mercury, found in high amounts in some fish. Methyl mercury accumulates in human tissue and, at certain levels, can impair cognitive development in young children – which is why the Food and Drug Administration (FDA) now says that children shouldn’t eat certain fish.
From studies of vaccines, scientists have concluded that ethyl mercury does not have the same effects as methyl mercury. In addition, research conducted by the National Institute of Allergy and Infectious Diseases has established that the body eliminates ethyl mercury much more quickly than it does methyl mercury, so ethyl mercury doesn’t accumulate in human tissue.
Is it true that children were exposed to unsafe levels of mercury from thimerosal?
From the mid-1980s until 1999, as shots were added to the list of routine childhood immunizations, children in the United States were exposed to more and more thimerosal. Some versions of the diphtheria-tetanus-pertussis (DtaP), Haemophilus influenzae type b (Hib) and hepatitis B vaccines, as well as the flu shot, contained the preservative.
In 1997 the FDA reviewed food and drugs containing mercury and found that some children may have been exposed to a total dose of 187.5 micrograms (mcg) of mercury from all sources during the first six months of life. This amount exceeded the Environmental Protection Agency guidelines for methyl mercury exposure. (There are no federal safety standards for ethyl mercury.)
As a precautionary measure, thimerosal was taken out of childhood vaccines in 2001. (The MMR vaccine, the chicken pox vaccine, the inactivated polio vaccine, and the pneumococcal conjugate vaccines never did contain thimerosal.) Since that time, research has concluded that thimerosal poses no risk to children.
In 2007, for example, the CDC published a study that evaluated over 1,000 children ages 7 to 10 years who received vaccines that used thimerosal as a preservative. The researchers found no association between exposure to thimerosal and neuropsychological functioning (such as speech and language skills, fine motor coordination, attention, and academic and intellectual functioning).
How can I tell if my child received vaccines that contained thimerosal?
If your child was vaccinated after the year 2001, it’s unlikely that they were exposed to more than trace amounts of thimerosal. In 1999 the Food and Drug Administration, the National Institutes of Health, and the Centers for Disease Control and Prevention, along with the American Academy of Pediatrics, asked vaccine manufacturers to reduce or eliminate the use of thimerosal in vaccines, and manufacturers took steps to comply.
Some doctors’ offices continued to use existing stockpiles of vaccines containing thimerosal, but experts believe they would have been used up by 2001 or 2002.
Isn’t thimerosal still used in flu shots and some others?
The only vaccines that currently contain thimerosal are multi-dose vials of the flu vaccine. Flu vaccines that don’t contain thimerosal as a preservative are available for both children and adults. (The flu shot is recommended annually for children 6 months and older.)
Ask your pharmacist or doctor if you want to know whether a flu vaccine contains thimerosal. It will be on the package list of ingredients. You can request a flu vaccine that’s thimerosal-free.
Again, thimerosal hasn’t been used in children’s vaccines since 2001.
What are the risks of not immunizing my child?
Medical experts agree that the benefits of vaccinating your child far outweigh the risks – for your child and for your community as a whole. A certain percentage of children have adverse reactions to vaccines, but such incidents are rare, given the large number of children vaccinated each year.
Julia McMillan, an emeritus professor of pediatrics at Johns Hopkins University in Baltimore, likes to remind parents about the number of serious diseases now controlled or eliminated by vaccinations.
“Many parents today are too young to remember the toll these diseases took before vaccines were developed,” she says. “Polio has not been seen in the United States for decades. Vaccines against Streptococcus pneumoniae, Haemophilus influenzae type b, and meningococcus have drastically reduced the frequency of bacterial meningitis and other invasive conditions due to these bacteria. Our vaccination program has been one of the most successful health campaigns – in terms of saving lives – in history. But it will only continue to be successful if people have their children vaccinated.”
If enough people decided not to be vaccinated, these illnesses could easily spread to epidemic proportions again. We know this is true because it has happened:
When measles vaccination rates in the United States dropped in the late 1980s, for example, more than 100,000 people came down with the disease and 120 died from it. In 1998, when immunization rates were back up, only 89 people became sick from measles and no one died. In 2000, measles was considered eliminated in the United States.
In 2019, however, 1,282 measles cases in 31 states were reported to the U.S. Centers for Disease Control (CDC). The majority of cases were among people who weren’t vaccinated.
Measles has definitely not been eliminated in other parts of the world, and it can easily be brought in by U.S. travelers and visitors from other countries. In addition to measles, other diseases, such as polio and diphtheria, are still only a plane ride away. And even if you and your family never leave the country, lots of people do travel, and they can unknowingly bring these diseases back with them.
The more people in your community don’t get vaccinated, the more quickly disease can spread throughout the population.
Where can I get more information on vaccine safety?
This is a complex issue, and given the widespread rumors and contradictory reports, it’s not surprising that parents are alarmed and confused. Start by talking to your child’s doctor.
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