A physician administers a vaccine to a child.
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  • A new study looked at a link between aluminum used in early childhood vaccines and the risk of developing asthma.
  • Experts are calling for more research to understand this risk.
  • Previous research on the link between childhood vaccines and asthma has been mixed.

A new study found a possible link between aluminum used in early childhood vaccines and the risk of children developing asthma before age 5.

However, the authors of the study caution that the results are not strong enough to suggest “questioning the safety of aluminum in vaccines.”

Instead, they call for additional research to better understand this risk. This might include studies using other large vaccine safety databases, and laboratory studies looking at children’s immune responses after vaccination.

Dr. Monica Gandhi, a professor of medicine at the University of California San Francisco, who was not involved in the new research, said it is important to reassure parents about the safety of vaccines.

“There is absolutely no indication at this point [that we should] change our vaccine formulations or recommendations on routine childhood vaccinations,” she said.

Previous research mixed

Aluminum is used in many vaccines as an adjuvant — which helps create a stronger immune response in people who receive a vaccine. 

Childhood vaccines that contain an aluminum adjuvant include: diptheria, tetanus and acellular pertussis (DTaP); hepatitis B; Haemophilus influenzae type b (HiB) vaccine; and pneumococcal conjugate vaccine.

The COVID-19 vaccines and seasonal flu vaccines do not use an aluminum adjuvant.

Previous research on the link between childhood vaccines and asthma has been mixed, the authors of the new study pointed out. 

One study found a small increased risk of asthma in children who received certain vaccines, while other studies found no increased risk or even a smaller risk of asthma.

None of these studies, though, looked specifically at exposure to aluminum in the vaccines, which the current study did.

In addition, rates of asthma among American children increased in the 1980s and 1990s, but have largely remained the same between 2001 and 2016, according to CDC data. So multiple factors are likely driving these trends.

Examining a potential vaccine-asthma link

The new study is based on electronic health records of nearly 327,000 children born between 2008 and 2014 who received care at seven sites that participate in the Vaccine Safety Datalink, a collaboration with the CDC to study vaccine safety.

The researchers divided the children into two groups — those with a diagnosis of eczema by 12 months of age and those without.

Like asthma, eczema is a form of allergic disease. Children with eczema also have a higher risk of developing persistent asthma. So if there is a link between aluminum in vaccines and the risk of developing asthma, it might show up differently in the two groups.

Researchers estimated each child’s exposure to aluminum by looking at how many vaccines they received before the age of 2.

They then looked to see which children developed persistent asthma between the ages of 2 and 5. Researchers defined persistent asthma as children having at least one inpatient healthcare visit or two outpatient or emergency department visits for asthma, and receiving at least two prescriptions for long-term asthma medication.

In both children with and without eczema, researchers found a positive association between exposure to aluminum in vaccines and the risk of developing asthma. The risk was higher for children with eczema.

This association remained when researchers accounted for other factors such as sex, race, ethnicity, food allergies, and number of healthcare visits. However, in some of the other analyses that the researchers did, the association was no longer present.

The study was published Sept. 27 in the journal Academic Pediatrics.

Other factors involved

Dr. James Gern, a professor of pediatrics and vice chair of research in the School of Medicine and Public Health at the University of Wisconsin-Madison, said that one of the strengths of the study is that it included a large number of children. Gern was not involved in the new study.

However, he said because this was a retrospective study — looking back at medical visits that have already happened —  it can raise questions, but can’t provide definitive answers.

One reason for this is that in this kind of observational study, it is impossible to rule out all “confounders,” said Gandhi.

These are factors — unrelated to aluminum in vaccines — that can increase or decrease a child’s risk of developing asthma.

For example, “aluminum is also found in dietary and other sources,” said Gandhi, such as breast milk, formula, and solid foods.

The authors of the new study did not have data on children’s dietary aluminum exposures. But some research suggests that “little to none of ingested aluminum appears to be absorbed,” so the absence of this data may not have impacted the results of the new study.

Other environmental factors — and genetics — can also increase a child’s risk of developing asthma.

So, “were [some children] more likely to have pets or grow up on a farm,” said Gern, “or did they have some other characteristic that protects them against asthma?”

More research is needed

Gern said prospective randomized clinical trials would be better able to determine whether aluminum in vaccines increases the risk of asthma. 

In this type of trial, one group of children would receive vaccines with an aluminum adjuvant, while a similar group of children would receive vaccines that are aluminum-free.

In terms of what this study means for routine childhood vaccinations, he said that the findings are not strong enough to question the safety of aluminum in vaccines.

Gandhi agreed: “The association [seen in the study] is very small and did not show a ‘dose-response’ effect [among children with eczema].”

A dose-response means that higher doses of aluminum would be associated with higher rates of asthma. “This is usually needed to show causality,” said Gandhi.

In spite of the limitations of the research, Gern said the results will “stimulate additional studies to see if aluminum in vaccines has anything to do with asthma.”

“The bottom line is that vaccines are still the best way to protect children against a whole host of dangerous infectious diseases,” he said.

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