According to a new observational study, there is a possible association between exposure to aluminum adjuvants in childhood vaccines and the development of persistent asthma in children ages 2-5. But the study does not conclude there is a need to question vaccine safety, and according to the Centers for Disease Control and Prevention (CDC) vaccines are safe and are essential to children’s health.
“Aluminum adjuvants have been an integral component to some childhood immunizations for over 70-years and have a well-established safety profile,” Dr. Tom Shimabukuro, Director of the Immunization Safety Office at CDC, explained to Bio.News. “While they’re not present in all vaccines, they are a key component to certain childhood immunizations. The reason being that they have long been known to improve immunogenicity (and thus the effectiveness) of vaccines.”
The study’s authors said the initial results may merit further assessment, but they conclude: “Considering the small effect size observed and the limitations described above, particularly related to unmeasured confounding, these findings do not constitute strong evidence for questioning the safety of aluminum in vaccines.”
According to the CDC, the study does not provide sufficient evidence to make changes to the Child and Adolescent Immunization Schedule.
So, what exactly did the study find, what does it mean, and how did it come about?
Initial concerns about aluminum adjuvants in vaccines
“The genesis of this study came from a report from the Institute of Medicine (IOM) – now the National Academy of Medicine – published back in 2013, on the safety of the childhood immunization schedule,” said Dr. Shimabukuro.
“The IOM realized that parents had concerns about the safety of the childhood immunization schedule as a whole—including longer-term health outcomes and exposure to certain vaccine ingredients like aluminum,” he continued. “Aluminum in small amounts is added to certain vaccines as an adjuvant, to help create a stronger immune response in people receiving the vaccine.”
“The IOM concluded that evidence supporting the safety of the schedule was strong, but it also identified areas for additional research,” continued Dr. Shimabukuro. “The IOM concluded that additional observational studies were the most appropriate way to approach this research because it’s not feasible or ethical to conduct randomized control trials, which would require withholding life-saving vaccines from children in the control group, for example.”
Clinical trials vs. observational studies
It is important to note the difference between clinical trials vs. observational studies.
Clinical trials have participants that receive specific interventions according to the research plan or protocol created by the investigators. For example, researchers may randomly (like flipping a coin) assign participants in a clinical trial to receive a new vaccine vs. a placebo injection.
By contrast, observational studies require investigators to assess health outcomes in groups of participants studied under real-world conditions according to a research plan or protocol. Observational studies are often retrospective, meaning the investigators look back in time to assess exposures, such as vaccines children received, and health outcomes diagnosed, like asthma.
The observational study findings
The recent observational study assessed for an association between aluminum adjuvants in vaccines and persistent asthma in young children using data from the CDC-sponsored Vaccine Safety Datalink (VSD).
The study consisted of 326,991 children and found that cumulative exposure to aluminum from vaccines during the first two years of life was associated with a small increased risk of persistent asthma in children ages 2-5.
“For this study, researchers looked at differences between children with and without eczema, because eczema is strongly associated with asthma risk. Therefore, a child with eczema is more likely to develop asthma in general. Among children with and without eczema, 6.0% and 2.1%, respectively, developed persistent asthma,” said the CDC in their press release on the study.
As a baseline, “the average amount of aluminum received from vaccines was about 4 mg in children with and without eczema. Among children without eczema, each additional 1 mg of aluminum received from vaccines was associated with a 1.2 times higher rate of persistent asthma and the study found similar results among children with eczema.”
But is there a biological reason for this correlation?
“There are different types of immune responses, and vaccines may bias the immune system towards one type of immune response versus another,” explained Dr. Shimabukuro. “Two types are T-helper 1 type immune-response and T-helper 2 type immune response. A T-helper 2 biased immune response could theoretically increase the risk of allergic diseases such as asthma. This theory is mainly based on animal data and hasn’t been proven in humans. T-helper 2 cells can contribute to airway hyper responsiveness in animal models, but caution should be exercised when attempting to extrapolate findings in animal models to humans.”
Establishing cause and effect from observational studies generally requires findings from multiple studies to ensure that the findings are repeatedly found (reproducible) and consistent across all studies. Given the findings identified in this single study, CDC is also looking for additional data sources that can be analyzed to further evaluate this potential safety concern. This effort is ongoing, but CDC hopes to have additional information on this to share in the coming months.
“The CDC takes vaccine safety seriously. We do not shy away from doing difficult scientific work and we are transparent in communicating our findings,” noted Dr. Shimabukuro.
Should parents be worried about asthma and vaccines?
Understandably, parents want to do what’s best for their children – and that’s still vaccinating them, according to the CDC’s recommended childhood immunization schedule.
“We recognize the new study results may be concerning for parents and caregivers,” the CDC report states, “however, there continues to be overwhelming evidence of the benefits of vaccines.”
There’s still substantial uncertainty around this study’s findings, but there’s no uncertainty around the benefits of childhood immunizations, which prevent disease and death in children.
“Vaccinating your child is still the best way to help them stay healthy and safe,” emphasized Dr. Shimabukuro.
