5 facts about vaccines

The scientific consensus is that vaccines prevent illness and save lives. But vaccinations have been subject to misinformation and confusion that’s having real-world consequences.

This year, 1,250 individual cases of measles have been documented in 31 states, marking the highest number of cases reported in the United States since 1992, according to the Centers for Disease Control and Prevention.

PolitiFact decided to research the topic, relying on scientific studies, government data, and independent experts and researchers. Here are five facts to know (and share) about vaccines.

Fact #1: Vaccines do not cause autism.

The inaccurate vaccine-autism link traces back to a 1998 paper by a British doctor who would later be stripped of his medical license after his study was found to be — in the words of the British medical journal BMJ — an "elaborate fraud." The UK’s medical licensing board ruled that lead author Andrew Wakefield deliberately falsified his research into a possible link between the measles, mumps and rubella vaccine (MMR) and autism. 

It took The Lancet, the prestigious medical journal that published Wakefield’s paper, 12 years to retract the study; by then the damage was done. Vaccination rates began falling. In the years after the publication of Wakefield’s study, the United States saw a significant rise in the rates of children who refused the MMR vaccine, while receiving all other recommended vaccinations. In England, vaccination rates fell from above 90% to 79%, and it took years for the numbers to bounce back.

There’s a lot we don’t know about what causes autism. But doctors we spoke with for a previous fact-check said you can definitively rule out vaccines. Decades of epidemiological research have demonstrated that autism rates do not increase when vaccines are introduced to a population. And no lab work has demonstrated a way for vaccines to cause autism.

There are instances when a child is developing normally but then experiences a drastic regression that results in severe mental impairment. It’s a type of autism known as childhood disintegrative disorder, and it affects about 1 in 10,000 children. In some instances — but not most — this change can occur around the time children are receiving vaccinations. The evidence shows that’s coincidental. 

"I’m a parent of a child with autism myself, and I completely understand a parent’s fear, and I don’t frown upon any parent who is concerned about it," said Kevin Pelphrey, director of the Child Neuroscience Laboratory at Yale. "But as a scientist, I absolutely know vaccines did not cause my daughter’s autism, and they do prevent diseases that kill children."

Fact #2: Measles are a serious illness that vaccines shield against.

Those who say measles aren’t so bad are suffering from a bout of historical amnesia. Let’s dial back the clock several decades, to the era before the MMR vaccine was widely administered in America.

"Before the ‘60s when we started vaccinating people, 400 to 500 people died every year in the United States from measles," Dr. Alan Melnick, the public health director in Clark County, Wash.,  told WBUR. "We had about 4,000 cases of measles encephalitis every year in the United States. That’s a swelling of the brain that can result in permanent damage and deafness." (Melnick’s county saw a measles outbreak in 2019.)

That bears repeating: Each year in America before the vaccine was common, up to 500 deaths, 4,000 cases of measles encephalitis and about 50,000 hospitalizations resulted from the highly contagious virus. 

Less developed countries, which have less access to vaccines, are still suffering. Around the world, an estimated 110,000 people died from measles in 2017, according to the World Health Organization. Most victims were under the age of five. Globally, measles is also one of the most common causes of blindness in children.

Fact #3: Childhood vaccines given in the United States do not contain mercury.

Childhood vaccines in the United States do not contain mercury. It’s a common misperception that they do, one which the anti-vaccination community often cites as evidence that vaccines contain poisonous ingredients that can cause autism.

Here’s the backstory of how this myth came to life. Before 1999, manufacturers included trace amounts of ethyl mercury, a component in the vaccine preservative thimerosal, in some childhood vaccines. Early vaccinations carried the risk of dangerous and sometimes lethal bacterial infections like staph infection, which killed four children in 1916. In response, starting in the 1930s, thimerosal was added to vaccines to keep multi-dose vials free from such bacteria.

The ethyl mercury found in thimerosal is relatively benign. The most common side effects are minor reactions like redness and swelling at the injection site. In rare cases people may be allergic to thimerosal, according to the CDC.

This brings us to another point of confusion. Ethyl mercury — the stuff found in the vaccine preservative thimerosal — is easily expelled from the human body in small quantities. Methyl mercury, on the other hand, is the compound found in fish and water, which builds up because the body can’t easily expel it. Some opponents to vaccines create confusion by using the term "mercury" for both ethyl mercury, and the more problematic methyl mercury.

Even though the ethyl mercury-laden thimerosal contained in vaccines is basically harmless, the Food and Drug Administration decided to remove thimerosal from all childhood vaccines after Wakefield’s erroneous study (described above).  

Thimerosal was removed and has not been used as a preservative in any vaccine on the recommended schedule for children since 1999. Flu vaccines are available in both thimerosal-containing and thimerosal-free versions.

Fact #4: Vaccines have been studied extensively, including in combined doses.

The notion that vaccines have not been studied in combined doses is false. As we noted in a previous fact-check, all vaccines are tested for years before and after being made available to the public, including "combined doses." 

The testing of vaccines, both singularly administered and given in conjunction with other vaccines, is a well-documented, years-long process that is critical for vaccine approval across the world.

Some parents have preferred in recent years to space out vaccines. But the CDC’s multiple vaccines information page reports that data shows getting several vaccines at the same time does not cause any chronic health problems. 

"A number of studies have been done to look at the effects of giving various combinations of vaccines," the CDC says, "and when every new vaccine is licensed, it has been tested along with the vaccines already recommended for a particular aged child."

Fact #5: Vaccine manufacturers are not above the law.

Vaccine makers in the United States are subject to laws aimed at encouraging widespread vaccination while compensating individual patients who have adverse reactions. In 1986, Congress passed the National Childhood Vaccine Injury Act that set up a federal program to pay families whose children reacted to mandatory vaccines. 

In addition to compensating families, the law shielded vaccine makers from liability. Congress did so to encourage pharmaceutical companies to continue making vaccines at a time of unfounded fears that the pertussis vaccine caused brain damage. 

Facing rising litigation and insurance expenses, some pharmaceutical companies exited the market, deciding it was too costly to produce the vaccine for pertussis, also known as whooping cough. This led to shortages in the vaccine supply, which the 1986 law sought to stabilize.

Two years after the law went into effect, the National Vaccine Injury Compensation Program launched. This program is funded by an excise tax on vaccines that the CDC recommends for children.

The Department of Health and Human Services, which administers the program, reports that 6,842 injury claims have been compensated since the first petitions were filed in 1989. In total, 18,269 injuries claims have been filed.

HHS notes that while most people who get vaccines have no serious problems, in some rare instances people do experience side effects, which are typically very mild. Severe allergic reactions are more rare, the agency said.

Injury claims are reviewed by a federal court-appointed official, known as a special master, who decides whether to grant compensation, and the amount. While pharmaceutical companies cannot be held liable under this special no-fault adjudication system, the protections they enjoy are not unlimited. 

Vaccine manufacturers have to properly manufacture the vaccines and could be found liable if they knowingly released a tainted vaccine. For example, under the Public Readiness Preparedness Act, a manufacturer of a vaccine may still be held liable, even after a PREP Act declaration, for "willful misconduct."

We should note that pharmaceutical companies produce many other drugs that are not protected from civil lawsuits. For example, Wyeth Pharmaceuticals was successfully sued in 2016 for "bundling" one of its drugs in sales to hospitals, thereby discouraging patients from switching to other, cheaper options.