A controversial European Union court decision about vaccines raises two interesting scientific questions: How do scientists decide whether vaccines can cause conditions such as autism or multiple sclerosis? And how certain can they be when they make their conclusions?
The June 21 ruling, which was more complicated than the headlines suggest, concerned a case of a Frenchman who was diagnosed with multiple sclerosis after being immunized against hepatitis B.
The EU court ruled that the courts of EU countries, including France, “may consider” circumstantial evidence when deciding whether a vaccine caused a disease when “medical research neither establishes nor rules out” a link.
According to a statement released by the EU court, circumstantial evidence could include “temporal proximity” between receiving the “vaccine and the occurrence of a disease” and a lack of family history of the disease.
To be clear, the EU court didn’t rule on the specific French case. It only clarified whether French law conflicted with EU law and ruled that it didn’t.
Law experts told us that the outcome of the French case will ultimately hinge on whether French courts say there’s enough scientific evidence to show there’s no link between the hepatitis B vaccine and multiple sclerosis.
Let’s first take a look at the specifics of the French case.
The Case of Mr. W
In 2006, Mr. W — which is how the Frenchman is identified in court documents — and three of his family members sued Sanofi Pasteur because they believed the pharmaceutical company’s hepatitis B vaccine caused Mr. W to develop multiple sclerosis.
Mr. W received vaccination against hepatitis B in December 1998, January 1999 and July 1999. He then “began to present with various troubles” in August 1999, which led to a multiple sclerosis diagnosis in November 2000. After his health “continued to decline progressively,” Mr. W died in 2011.
Multiple sclerosis, or MS, is a chronic disease where the immune system attacks the nervous system, including the brain and spinal cord, explains the National Multiple Sclerosis Society. Most people die from complications related to the disease. But “in some rare instances,” where the onset of MS is rapid, people do die from the disease, the society says.
Certain genes have been linked to the disease, but there’s “no evidence that MS is directly inherited,” the society adds. Environmental factors, such as low Vitamin D and cigarette smoking, have also been linked to an increased risk of the disease.
French law says that to win a case like Mr. W’s, a “causal link” between a vaccine “defect” and “damage suffered by the person” must be “derived from serious, specific and consistent presumptions.” But what does that mean?
In this particular case, the family pointed to the fact that Mr. W began experiencing symptoms of MS shortly after receiving the hepatitis B vaccine. They also noted he had no family history of the disease.
The suit was first upheld in a regional court in Nanterre, France, in 2009 and then overturned in an appeals court in Versailles in 2011. The appeals court ruled that Mr. W and his family had provided sufficient evidence to prove the vaccine caused his disease, but not that the vaccine was defective. The case was then brought to a higher court in France, the Court of Cassation, which overturned the Versailles appeals court decision, arguing it had no “legal basis.”
The case then went to an appeals court in Paris that ruled in favor of Sanofi Pasteur. The family’s circumstantial evidence ran counter to scientific evidence, so it couldn’t prove a causal link between the vaccine’s administration and Mr. W’s disease, the Parisian court said.
What was that scientific evidence? The appeals court said “there was no scientific consensus supporting a causal relationship between the vaccination against hepatitis B and multiple sclerosis.” It also noted that “all the national and international health authorities had rejected the association.”
Specifically, the court reasoned, scientists don’t know what causes MS and research shows 92 percent to 95 percent of people with the disease have no history of it in their families. The court also noted that research suggests symptoms of MS “probably” first appear “many months, or many years” after the disease begins affecting the body on a cellular level.
The case then went back to the Court of Cassation, which decided to ask the EU Court of Justice for legal guidance. It asked whether French courts could take into consideration the kind of circumstantial evidence provided by Mr. W’s family under EU law. In cases where the science is unclear, the EU court said circumstantial evidence could constitute sufficient legal evidence to prove that a vaccine caused a disease.
Multiple law experts have said that the EU court didn’t rule that French courts can disregard science, as headlines suggested. Vaccine manufacturers can use any scientific evidence that’s available in their defense, experts said.
Still, it’s unclear how the French courts will rule on Mr. W’s case. Law experts told us it hinges on how they’ll interpret a specific clause in the EU court’s ruling, namely that circumstantial evidence can be used when “medical research neither establishes nor rules out the existence of a link between the administering of the vaccine and the occurrence of the victim’s disease.”
Dorit Rubinstein Reiss, a professor of law at the University of California, Hastings, told us by phone that a “responsible court” would rule in favor of Sanofi Pasteur because there’s enough scientific evidence against a link between the hepatitis B vaccine and multiple sclerosis.
But Richard Goldberg, a professor of law at Durham University in the U.K., told us the EU decision requires scientists to definitely “rule out” a relationship between a disease and a vaccine, not just have more evidence against a link than evidence supporting one. Since scientists can’t rule out anything, the language of the decision creates a loophole to stifle the use of scientific evidence in court, he told us over the phone.
Establishing Causation in Science
According to a vaccine committee at the Institute of Medicine of the National Academies, Goldberg is right that it’s difficult, if not impossible, for scientists to definitively rule out that a vaccine causes a disease.
In a 2012 report on vaccine safety, the committee used four “categories of causation” when evaluating whether a vaccine causes an “adverse effect.”
- Evidence convincingly supports a causal relationship
- Evidence favors acceptance of a causal relationship
- Evidence is inadequate to accept or reject a causal relationship
- Evidence favors rejection of a causal relationship
But the 2012 report says the committee doesn’t use the category “establishes or convincingly supports no causal relationship” because it’s “virtually impossible to prove the absence of a relationship with the same certainty that is possible in establishing the presence of one.”
Why? Because “studies may not rule out the possibility that the reaction is caused by vaccine in a subset of individuals,” the committee says.
Alberto Ascherio, a professor of epidemiology at Harvard who has studied whether the hepatitis B vaccine causes MS, elaborated on this point.
Scientists can study “counterfactuals” in populations, but not individuals, he told us over the phone. That is, they can’t examine what would have happened if an individual person hadn’t received a vaccine, compared to if they had. But scientists can look at the rate of vaccination in a population of people who have a disease and compare it to the rate in a population of people who don’t.
That’s exactly what Ascherio and his colleagues did in a study published in the New England Journal of Medicine in February 2001. They compared the rate of hepatitis B vaccination in nearly 192 women with MS to the rate in 645 women who don’t have the disease. They found “no evidence of an increased risk” hepatitis B vaccination and MS.
To evaluate whether there’s a causal relationship between the hepatitis B vaccine and MS, the vaccine committee at the Institute of Medicine considered Ascherio’s study among three other epidemiological studies. Epidemiological studies look at disease rates in populations of people. The vaccine committee excluded a number of other studies, some that did find a link and some that didn’t, due to methodological concerns.
Of those considered, three studies, including Ascherio’s, didn’t find any evidence for a link, and one study did.
In addition to considering epidemiological evidence in its evaluation of whether the hepatitis B vaccine causes MS, the vaccine committee looked at mechanistic evidence to support or refute a causal link. This kind of evidence primarily consists of experiments done on animals, such as mice, and humans.
For example, scientists might vaccinate mice against hepatitis B and see how many of them show symptoms of MS. They might also investigate what occurs on a cellular level when mice are exposed to the vaccine. In other words, this kind of evidence elucidates the possible mechanisms, or biological processes, by which a vaccine could cause a disease.
By integrating population level (epidemiological) and individual and cellular level (mechanistic) evidence, scientists can assess whether a vaccine causes an adverse effect, such as a disease.
In the case of MS and the hepatitis B vaccine, the vaccine committee found no mechanistic studies that met their methodological standards.
And then there’s the one epidemiological study considered by the committee that did find an association. Published in the journal Neurology in September 2004, the study compared the rate of hepatitis B vaccination in 163 people with MS to the rate in 1,604 people who don’t have the disease.
Given the “limited confidence” in the epidemiological evidence and the “lacking” mechanistic evidence, the committee concluded, “evidence is inadequate to accept or reject a causal relationship between hepatitis B vaccine and onset of MS in adults.”
Miguel Hernan, also a professor of epidemiology at Harvard and the lead author of the 2004 Neurology study, told us by email that the 2012 “report’s conclusion is consistent with [his] own assessment of the literature through 2007.” He added, “Last time we wrote about this issue (in 2006-2007), we argued that nothing more definitive could be said until new studies were performed.” The 2012 report didn’t consider any studies newer than 2007.
But Ascherio, the author of the epidemiological study that didn’t find a link, told us by email that he thought the committee’s conclusion was “potentially misleading” because it didn’t “give enough credit” to the epidemiological studies that didn’t find a link.
It’s also important to note that the Centers for Disease Control and Prevention and the World Health Organization both think there’s enough evidence to conclude there’s no link between the hepatitis B vaccine and MS.
“Hundreds of millions of people worldwide have received [the] hepatitis B vaccine without developing MS or any other autoimmune disease,” the CDC says. “As with all vaccines and any disease, due to the large number of vaccinations administered worldwide, surveillance systems that monitor health concerns after vaccination do expect to receive reports of MS occurring after vaccination that happen by chance alone.”
The WHO also attributed the cases of people developing MS after hepatitis B vaccination to coincidence.
When it comes to whether the measles, mumps and rubella vaccine causes autism, the science is more clear. The vaccine committee at the Institute of Medicine concluded in its 2012 report: “The evidence favors rejection of a causal relationship between MMR vaccine and autism.”
The committee had a “high degree of confidence” that the epidemiological evidence suggests there is no link. However, the mechanistic evidence is “lacking,” the committee concluded. That’s because scientists aren’t sure what causes autism in the first place.
Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.