Study does not prove link between aluminum in childhood vaccines and asthma, experts say
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Experts said a recently published study that found a possible association between aluminum in childhood vaccines and persistent asthma in early childhood did not prove there was a link.
The American Academy of Pediatrics published a story online with comments from James D. Campbell, MD, MS, vice chairperson of its committee on infectious diseases, who said that he welcomed the research and stressed that safety is a top priority in pediatric vaccines.
“The overwhelming benefit of the vaccines and the long-term safety we’ve seen from them should reassure parents they should still completely vaccinate their children,” Campbell said.
The AAP included a statement from the CDC, which said it “agrees with the authors [of the study] that this single observational study has important limitations and does not show that aluminum in some childhood vaccines can cause development of persistent asthma.”
The CDC said it would not be changing its routine childhood vaccination recommendations based on the results.
The CDC-funded study was conducted by Matthew F. Daley, MD, a pediatrician and senior clinician investigator at the Kaiser Permanente Colorado Institute for Health Research and associate professor in the department of pediatrics at University of Colorado School of Medicine, and colleagues.
They assessed a cohort of 326,991 children born between Jan. 1, 2008, and Dec. 31, 2014, and observed through Dec. 23, 2017, “to examine the association between cumulative vaccine-associated aluminum exposure before age 24 months and persistent asthma incidence at age 24 through 59 months.”
Of the total cohort, 4.4% were diagnosed with eczema by age 12 months, of whom 6% also had persistent asthma. Of the children without eczema, 2.1% had persistent asthma. The mean vaccine-associated aluminum exposure was 4.07 mg (standard deviation [SD], 0.6) in children with eczema and 3.98 mg (SD, 0.72) in children without eczema.
The researchers found that among children with eczema, vaccine-associated aluminum was positively associated with persistent asthma (adjusted HR = 1.26 per 1 mg increase in aluminum; 95% CI, 1.07-1.49) at age 24 through 59 months. They also detected a positive association among children without eczema (aHR = 1.19; 95% CI 1.14-1.25).
Given the small effect size and limitations including misclassification of vaccine-associated aluminum exposure, “these findings do not constitute strong evidence for questioning the safety of aluminum in vaccines,” the researchers wrote.
“However, additional examination of this hypothesis appears warranted,” they continued.
In an accompanying commentary, Andrew D. Racine, MD, PhD, chief medical officer at Montefiore Medical Center and chief of the division of general pediatrics at the Albert Einstein College of Medicine, said the results do not definitively establish an association between vaccine-related aluminum exposure and persistent asthma development.
He called the study’s findings “intriguing” but cautioned readers to interpret the data carefully.
“The pediatric community is daily witness to the power of vaccines to mitigate, even to eradicate, severe suffering and death. And we remain, in midst of other woes, surrounded by misinformation, politicization, and occasional delusional thinking regarding this verifiably beneficial tool,” Racine wrote. “Yet despite whatever unwarranted claims and speculations persist about vaccinations, as scientists, as stewards of public health, we must be ‘prepared to see’ possible complications from their use.”
References:
AAP: Study of aluminum in vaccines does not change vaccine recommendations. https://publications.aap.org/aapnews/news/22376/AAP-Study-of-aluminum-in-vaccines-does-not-change?autologincheck=redirected?nfToken=00000000-0000-0000-0000-000000000000. Published Sept. 27, 2022. Accessed Oct. 5, 2022.
Daley MF, et al. Acad Pediatr. 2022;doi:10.1016/j.acap.2022.08.006.
Racine AD. Acad Pediatr. 2022;doi:10.1016/j.acap.2022.08.007.
Perspective
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The authorship of this study reflects the very best partnership of experts in vaccine safety across institutes of health research, health care and public health. The Vaccine Safety Datalink (VSD), a national research network, was established to perform large post-licensure/authorization observational studies such as this — seeking occurrence of specific uncommon adverse events as possibly related to certain vaccine(s) — for example, Guillain-Barré syndrome, intussusception, myopericarditis.
The current study entailed 5-year observation of a cohort of more than 300,000 young children. The investigators’ diligence to get the population, exposure and outcome “right” is evident in enrollment inclusions and exclusions, quantification of vaccine-related aluminum exposure using enrollees’ health records, use of strict criteria for the outcome of persistent asthma, performance of exacting statistical analysis and multiple secondary analyses, and use of all-cause injuries as a negative control outcome. The authors got the best study possible, interpreted the data correctly and concluded appropriately. And yet, the bottom line is that this study does not establish a firm link between vaccines and asthma, nor should it diminish enthusiasm for immunization, or elicit a change in vaccine products or schedules. But the results generate a hypothesis.
The only modest effect size of aluminum received in vaccines on asthma diagnosis and the inability to know that the cohorts and exposures were wholly similar except for aluminum in vaccines leaves the likelihood of residual confounding by unrecognized bias as a possible or even likely explanation of findings. It is noteworthy that observed aluminum effect diminished as cohort analyses were restricted to more seemingly “like” groups (eg, fully vaccinated only, breastfed only). Additionally, the absence of ability to examine social and economic determinants of health — especially important in asthma — leaves unknown bias squarely on the table.
Was use of certain vaccine products with more or less aluminum tied to types of providers serving dissimilar populations? Predisposition to asthma is a complex puzzle, with the host, the environment, the microbiome and early antibiotic exposure all thought to be relevant pieces. Aluminum was in vaccines for decades before the rise in asthma. Host responses to whole-cell (DTP) and acellular pertussis (DTaP) vaccines — both including aluminum — have been studied, showing a skewed Th1 direction of the former and Th2 direction of the latter. It seems unlikely that aluminum is a key driver of signature immune responses.
Kudos to The National Academy of Medicine (then the Institute of Medicine) for encouraging studies of risk for chronic conditions following vaccination and for that methodologic challenges will be substantial. Kudos to authors for performing such a thoughtful study and for bringing the results to light, certainly knowing the potential for harm from overinterpretation or false representation. Parents should be reassured that vaccine safety is being scrutinized continuously and that no results are hidden from the scientific world, their providers or them. With hypothesis generated, we await another or a next study that can more robustly answer the question raised.
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