Vaccine Safety: New Report Finds Few Adverse Events Linked to Immunizations

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John Giustina

In a new report investigating adverse events caused by vaccines, a panel of experts says there are relatively few health problems caused by the most commonly recommended immunizations, which public health experts advise that all children receive.

The conclusions, issued by the Institute of Medicine (IOM) in its latest report, “Adverse Effects of Vaccines: Evidence and Causality,” represent the most comprehensive review of the available literature on the potential side effects of eight vaccines — for mumps, measles and rubella (MMR); chicken pox; influenza; hepatitis A; hepatitis B; human papillomavirus (HPV); diphtheria, tetanus and pertussis (DTAP); and meningococcus.

The committee responsible for the IOM report included experts in pediatrics, immunology, neurology, epidemiology and statistics, who analyzed more than 1,000 studies published in peer-reviewed journals concerning the health consequences of the eight immunizations.

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Of note, they conclude that there is no evidence to support a connection between the MMR vaccine and autism, as many parent groups continue to believe, spurred on by the claims of British physician Andrew Wakefield, who lost his medical license last year when his findings were found to be fraudulent. The committee’s report joins many other past studies that have come to the same conclusion that vaccines and autism are not related.

The committee members also decided that there isn’t evidence at this time to link the flu shot to episodes of asthma. They did, however, report that the HPV vaccine, the most recent shot added to the immunization schedule, may cause anaphylactic shock in some people, and that the MMR shot can trigger joint pain.

“This is the most comprehensive, most careful analysis of all of the literature looking at these eight vaccines that has ever been done,” Dr. Ellen Clayton, chair of the IOM committee that authored the report and professor pediatrics at Vanderbilt University, told TIME. “It is state of the art.”

The 18-member committee looked at two kinds of studies concerning adverse events of vaccines. First they analyzed epidemiological, or population-based studies that track reports of health problems following vaccinations. Then they reviewed biological data that detailed individual reports of adverse events after immunizations and provided information on how the innoculations may have contributed to whatever health problems that were associated with them. The committee’s task, says Clayton, was simply to document whether any adverse effects were associated with vaccines, in order to be able to present to doctors, parents and public health experts the latest data on what to expect when people receive the shots.

The committee did not assess how frequently the negative health effects occurred, however, nor did they conduct an analysis of risks versus benefit to determine how any potential side effects measured up against the benefits of being protected from infection.

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Overall, the committee made 158 conclusions that fell into one of four categories:

  • The evidence supports a causal relationship between the vaccine and the adverse event
  • The evidence seems to favor a causal relationship, but isn’t as convincing yet
  • The evidence in inadequate to either accept or reject a causal relationship
  • The evidence favors rejection of a causal relationship

Not surprisingly, the vast majority of their decisions — 133 — fell into the inadequate category, including many concerns associated with the HPV vaccine. But that doesn’t mean that the data is simply inconclusive, says Clayton. In fact, that category is quite diverse, encompassing cases in which studies show both a potential connection or no connection between vaccines and an adverse event; it also includes cases in which the information simply doesn’t exist — yet —to make a sound scientific conclusion. That’s the case with HPV, which hasn’t been used long enough in enough people to generate robust data on many of the potential side effects, such as neurological conditions that have been linked to the vaccine in some.

For many of the cases in which it’s not clear whether a vaccine can cause a specific health problem, Clayton says she hopes more information will become available in coming years to address those gaps. “If we think about what was known 20 years ago when the last studies were done about how adverse events could occur, our understanding of the biology and what the mechanisms of adverse events might be paled in comparison to what we know now,” she says. “One hopes that in the future our current state of knowledge will pale in comparison to what we know in 20 years.”

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Because the report does not weigh the benefits and risks of getting vaccinated, but simply lays out the latest data on any potential side effects associated with the inoculations, parents who are struggling with concerns about getting their children vaccinated may not find the answers they are looking for in this review.

For one, the report did not consider the question that many moms and dads are currently asking: Is giving multiple vaccines so close together, or even in one day, harmful? The committee could only review studies of people who were vaccinated according to the currently recommend schedule, which does indeed advise multiple vaccines on a single day, so they did not have data on people who might have received their shots separately.

But the report will become a valuable resource for doctors who need to address parents’ questions, by giving them the most comprehensive data available on the adverse events linked to these eight vaccines. In addition, the data will also be useful for the National Vaccine Injury Compensation Program, a no-fault alternative for compensating individuals who may have been harmed by vaccines.

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“As a practicing pediatrician, the ready availability of a report like this specifically identifying each vaccine and specifically identifying each adverse event that summarizes the world’s literature objectively is extraordinarily valuable,” Dr. Douglas Barrett, a pediatrician at University of Florida College of Medicine and a member of the IOM committee, told reporters during a telebriefing.

It’s certainly not the last word on vaccines and adverse events — as the large number of ‘inadequate information’ conclusions demonstrates, but it’s an important step in helping to inform physicians and the public about the latest scientific knowledge on how vaccines affect all of us.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

2 comments
SubarjoTuan
SubarjoTuan

The committee members also decided that there isn’t evidence at this time to link the flu shot to episodes of asthma. They did, however, report that the HPV vaccine, the most recent shot added to the immunization schedule, may cause anaphylactic shock in some people, and that the MMR shot can trigger joint pain.

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