NEW YORK (AP) — A number of scientists have questioned whether aluminum, a vaccine additive that has been used for decades, has a role in childhood allergies and asthma.
A new federally funded study has found a possible link, but experts say the research has significant gaps and is no reason to change current vaccine recommendations. The study does not claim that aluminum causes the respiratory disease, and officials say more work is needed to try to confirm any link, which had not been seen in previous research.
Even if a link were ever found, the life-saving benefits of vaccines are still likely to outweigh the risk of asthma, said Dr. Matthew Daley, lead author of the study. But it’s possible that if the results are confirmed, it could spur further work to redesign the vaccines, he added.
Dr Paul Offit of Children’s Hospital of Philadelphia feared the flawed study would unnecessarily scare some families from proven vaccines.
“Making an extraordinary claim requires extraordinary evidence,” Offit said. This study doesn’t offer that kind of evidence, he said.
He and other outside experts noted that Daley and his colleagues were unable to account for the effects of some potentially significant ways children are exposed to aluminum, such as through the air or through their diet.
They also noted that the results included hard-to-explain inconsistencies, such as why, in a subset of thousands of fully immunized children, greater aluminum exposure did not appear to lead to higher asthma risk.
CDC officials, in a statement, said it appears aluminum-containing vaccines “do not account for the general trends we are seeing.”
The study, published Tuesday, suggests that young children who were immunized with most or all of the recommended aluminum-containing vaccines were at least 36% more likely to be diagnosed with persistent asthma than children who received fewer vaccines.
Aluminum has been used in some vaccines since the 1930s, as an ingredient – called an adjuvant – that causes stronger immune protection.
By age 2, children should be vaccinated against 15 diseases, according to US recommendations. Aluminum adjuvants are present in vaccines for seven of them.
Aluminum adjuvants have long been considered safe and effective. Yet scientists have noted a period of rising allergy and asthma rates among American children over a 30-year period beginning around 1980, and some have wondered if there was a link. (These rates stabilized about a decade ago and have declined somewhat in recent years, for reasons that are not fully understood.)
Several previous studies have not found a link between childhood vaccines containing aluminum and allergies and asthma. But other research has linked aluminum in industrial workplaces to asthma. And the aluminum-injected mice suffer an immune system reaction that causes the kind of airway inflammation seen in childhood asthma.
“Based on what I consider to be limited animal data, there is a theoretical risk that aluminum in vaccines could influence allergy risk,” said Daley, associate professor of pediatrics at the medical school. from the University of Colorado.
In 2013, the Institute of Medicine — now known as the National Academy of Medicine — called for more federal research into the safety of childhood vaccines, including their use of aluminum.
The new study is part of the government’s response to that call, Daley said. It was funded by the CDC and included current and former CDC staff among its authors. It was published by the medical journal Academic Pediatrics.
The researchers focused on approximately 327,000 US children born between 2008 and 2014, looking to see if they had received aluminum-containing vaccines before age 2 and if they had developed persistent asthma between age 2 and 5 years.
Asthma, a condition that can cause spasms in the lungs, usually results from an allergic reaction. About 4% of American children under the age of 5 have persistent asthma.
The researchers took steps to try to account for different factors that could influence the results, including race and ethnicity, whether the children were born premature, or whether the children had food allergies or certain other conditions.
But there were many other factors they were unable to address. For example, aluminum can be regularly found in breast milk, infant formula, and food, but researchers were unable to obtain data on how much aluminum children consumed. They also had no information about aluminum exposures from the air and environment where the children lived.
The researchers divided the study group into two. One involved around 14,000 children who developed eczema, a skin condition thought to be an early indicator of the development of asthma or other allergic diseases. They wanted to see if children with eczema were more or less sensitive to aluminum in vaccines, compared to children who didn’t have early eczema. The approximately 312,000 other children in the study did not have early eczema.
Both groups got about the same amount of vaccine-bound aluminum. Researchers found that for every milligram of aluminum received through vaccines, the risk of persistent asthma increased by 26% in children with eczema and 19% in children without eczema .
Overall, children who received 3 or more milligrams of vaccine-related aluminum had at least a 36% higher risk of developing persistent asthma than children who received less than 3, Daley said.
Offit said the limitations of the study meant the work had “added nothing to our understanding of vaccines and asthma”.
But other experts said the researchers drew on a respected body of patient data and worked carefully with the best information available.
“This is public health at its best. They’re doing everything they can to find any possible signals that might be of concern,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “It’s our job to examine this comprehensively to see if it’s true.”
He acknowledged that anti-vaccine campaigners are likely to draw conclusions that the evidence does not support. But if the CDC had the information and did not release it, the agency could be seen as misleading the public, further eroding trust, he said.
Dr. Sarah Long, professor of pediatrics at Drexel University College of Medicine, echoed this.
“I believe in full transparency,” she said. “If you asked a question and spent our (taxpayer’s) money here to (investigate) that question, I think the results should be out in all its warts and glory.”
The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute Department of Science Education. The AP is solely responsible for all content.