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Safe Vaccines and Healthy Children

An Interview with Dr. Saad B. Omer on Vaccine Policy

Female nurse administering a shot to young boy SOURCE: AP Vaccine safety has grabbed headlines in recent months, as some parents, fearing alleged links to autism, exempt their children from vaccinations. Multiple studies have demonstrated there is no such link, but there is more to understand about how vaccines keep kids safe, and how public health experts ensure the safety of vaccines.

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The Centers for Disease Control publishes a Parent’s Guide to Childhood Immunizations, which states in no uncertain terms: “Immunization has been called the most important public health intervention in history, after safe drinking water. It has saved millions of lives over the years and prevented hundreds of millions of cases of disease.” With a regular schedule of vaccines for young children in the U.S., a whole slate of dangerous infections are now uncommon or virtually non-existent in this country.

But a British study published in 1998 drew a link between the measles-mumps-rubella vaccine and autism. While the study itself was flawed and discredited, and subsequent research has demonstrated no link between vaccines and autism, parents and advocacy groups are still wary.

To learn more about vaccine safety, Science Progress spoke with Dr. Saad Omer, the associate director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health. Parents concerned about vaccine safety, he says, are coming from the right place in terms of their desire to protect their children, and that it is the responsibility of the public health community to broadcast the right information so that people can make informed decisions about the risks and benefits of vaccines and vaccine-preventable diseases. This interview has been edited.

Andrew Plemmons Pratt, Science Progress: Some recent media coverage has focused on the March ruling from the National Vaccine Injury Compensation Program to Terry and John Poling, who claim that a vaccine contributed to their daughter Hannah’s development of autism. In a New York Times editorial, Paul Offit of the Children’s Hospital of Philadelphia laments the fact that the program abandoned a previous standard for a “preponderance of evidence” for determining the link between vaccines and injuries and instead ruled that their claim was made on standards of “biological plausibility.” Is there a problem with the way that vaccine injury compensation program ruled on this issue, and what does it say about the way we are approaching vaccines in general?

Dr. Saad B. Omer: Let me start with the case, to briefly describe it for those who are not familiar with it. It was a case of a nineteen-month-old girl who received several vaccines together after a delay due to current bouts of otitis media, or an ear infection. And so those vaccines were administered together and she developed some symptoms after that, and at the twenty-three month assessment she was diagnosed with having mild symptoms of autism spectrum disorder, and during her evaluation she was diagnosed with a mitochondrial disorder. A claim was filed in a federal court, and the government settled, awarding them compensation for that.

So to put things in perspective for that case—and in terms of people drawing conclusions from it—I would caution that this is just a case and the question I often ask, even within the scientific community is “where are the controls?” Because when we assess scientific evidence, we need to keep in mind that we need to compare an association of an event with an outcome in both cases and controls, we haven’t had that kind of evaluation yet. And I can go into specific examples of what problems one can have. However, this is a “biologically plausible hypothesis.” What does that mean? That means we should explore this kind of hypothesis under a counterfactual model but should not draw conclusions from it at this point.

And just to clarify why we are on this topic: even if this link is established, and what it says is that mitochondrial disorders, which are a kind of disorder in the cell’s energy mechanism, is proven to be exacerbated by vaccines and result in autism spectrum disorders, metabolic disorders are very rare and it would explain a very small proportion of autism diseases—just to put that in perspective.

Now to the second part of your question, about the change in the standard in the vaccine court that resulted in the awarding of this compensation. First of all, it wasn’t the injury compensation program that changed it, it was the interpretation of a couple of circuit court decisions. These higher court decisions were the result of some cases from the compensation program that were appealed and there were a couple of decisions which the Special Masters of the compensation program, not the HHS, interpreted as having said that the evidence should be evaluated on a standard of “biologically plausible.” I think that’s dangerous, because I can sit here and come up with twenty or thirty different hypotheses which would be biologically plausible on several biological models. We are not talking about probable; we are talking about plausible. Even with probable models, we know the human body is complex, and if you test twenty different biological hypotheses, a majority of them won’t pan out in humans. So I think it’s not a very robust standard to go by because what we are saying is that we would have judgments on these cases based on something that could happen, not something that does happen.

SP: The government has programs that do vaccine surveillance and maintain safety. Could you talk a little bit about what those programs are and how effective they are?

Omer: One major program is the Vaccine Adverse Events Reporting system, which is jointly managed by the CDC and the FDA, and events that seem to be associated with vaccines are reported into that system. It’s a good system for generating signals but it has its limitations. The major limitation is that we don’t have a good denominator to calculate rates so we cannot assume all the vaccine doses that entered the market were administered, so we don’t know the rates.

But another interesting problem that has come up is due to the fact in the U.S. adverse event reporting system, anyone can report a case into the system. There was a recent analysis published in Pediatrics that showed that most of the rise in reports of autism-related symptoms associated with vaccines has been due to increased reporting of litigation-associated cases. So we have that kind of a problem with VAERS but it still has a lot of utility in terms of generating signals. For example, it generated a signal for the old rotavirus vaccine.

Then the CDC has the Vaccine Safety Datalink. They have put together a system by linking databases from several large HMOs, and it covers approximately two percent of the U.S. population of zero to six years. Fortunately because vaccine events are rare, you need large databases to get enough numbers and do a robust scientific study, so that’s a good system.

Then there is the Clinical Immunization Safety Assessment Network, which is a network of a few centers of excellence, mostly academic centers, coordinated by the CDC, to assess vaccine safety in a clinical setting.

So this is basically what the vaccine safety system is in the U.S. However I must say, I think vaccine safety needs a lot more resources than it is provided. Because as I said, vaccine events are rare so you need large numbers to study these phenomena and the resources that are available are very low.

SP: These are very personal choices that parents are making about whether or not to exempt their children from getting vaccinations. What do you say to parents who might be thinking of exempting their children from getting vaccines because of what they might have heard about these possible links to autism?

Omer: There have been several studies—both in the U.S. and outside, in Denmark and other parts of Europe—that have looked at the issue of vaccines and autism and we haven’t found any credible association between vaccines—either thimerosol, which is a mercury preservative that was of concern a few years ago—and MMR, the measles mumps and rubella vaccine and autism. So there have been several studies, and our website,, discusses some of these issues so people can go and look up specific evidence related to that.

On the other hand, we know that there is risk of—even an individual level risk—of acquiring vaccine-preventable diseases in the United States if your child is not vaccinated. For example, in a national-level study it was found that kids who are exempt from vaccination requirements had thirty-three times—not percent, it’s times—higher risk of acquiring measles with those who are vaccinated, who do not seek exemptions, and [in a Colorado study] six times higher risk of acquiring pertussis than those who are vaccinated. So there are real risks involved in terms of acquiring vaccine-preventable diseases

One last point in this regard: we do know that congenital rubella syndrome is associated—and there are some studies showing an association—with autism-like symptoms. So we know that part of that syndrome is explained by a congenital rubella syndrome which used to occur when the population-level immunity in the U.S was relatively low. So actually, MMR vaccine prevents against something that is associated with autism. So if you are thinking specifically in terms of autism, one should consider that we are talking about something that prevents autism. Congenital rubella syndrome is when mothers get rubella in pregnancies, and children develop certain abnormalities.

SP: So in your experience, where does this misinformation about the risks of vaccination come from? Is it usually generated through parents talking to parents? Is it the media? Is it doctors talking to parents?

Omer: It’s several sources. We found in our studies—looking at parents of children exempted from vaccination requirements, compared to those vaccinated—there was an association with types of provider, trust in government, the sources of information people tended to get, information from some of the advocacy sites tended to seek exemptions at a higher rate, etc. So yes. There are several sources of that, and there are passionate people who feel there is an association with vaccines and autism, and that includes some celebrities as well. So that gets people’s attention.

On the other hand I must say that most parents, even those that are concerned about vaccine safety, are coming from the right place. All of us want our children to be safe from any harm, including harm from any pharmaceutical interventions. So we shouldn’t be dismissive of that, but it’s our responsibility, for those of us in the public health community, to put out the right information so that people make a truly informed decision about the risks and benefits of vaccines and vaccine-preventable diseases.

SP: What do you think is most important for people who are both working in the public health community, people who are policymakers, people who might be hearing about this issue, and for parents to take away from this whole conversation in the public sphere at the moment?

Omer: One thing that people should realize is that we know that vaccines have some side effects. And we should acknowledge that, everyone who is involved. However, the risk and benefit calculus for all vaccines that are out there, based on our current knowledge, heavily favors not only getting your child vaccinated, but also getting them vaccinated according to the specified schedule. I have seen a new trend where people are splitting the difference and saying, “OK, I’m going to get my kid vaccinated, but I’m going to get them vaccinated late.” Well the risk of illness is not constant across childhood and so that’s why the Advisory Committee on Immunization Practices and the American Academy of Pediatrics come up with these recommendations to look at several factors, including the burden of disease. So it’s important to not only get your child vaccinated, but also to get them vaccinated per specified schedule.

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