NEW YORK (AP) – Several scientists have questioned whether aluminum, a vaccine additive that has been used for decades, played a role in allergies and asthma in children.
A new federally funded study has found a possible link, but experts say the research has significant shortcomings and is not a reason to change current vaccine recommendations. The study does not claim that aluminum causes the breathing condition, and officials say more work is needed to try to confirm any connection, which has not been seen in previous research.
Even if a link were ever found, the life-saving benefits of vaccines would likely outweigh the risk of asthma, said Dr. Matthew Daley, the study’s lead author. But it’s possible that if the results are confirmed, it could lead to new work to redesign vaccines, he added.
Dr. Paul Offit of the Children’s Hospital of Philadelphia worried that the flawed study would unnecessarily scare some families away from the tested vaccines.
“Making an extraordinary claim requires extraordinary evidence,” Offit said. This study doesn’t provide that kind of evidence, he said.
He and other outside experts noted that Daley and his colleagues failed to account for the effects of some potentially important ways in which children are exposed to aluminum, such as in the air or through their diet .
They also noted that the findings include inconsistencies that are difficult to explain, such as why, in a subset of thousands of fully vaccinated children, more aluminum exposure did not appear to lead to a greater risk of asthma.
CDC officials, in a statement, said it appears that aluminum-containing vaccines “do not account for the general trends we see.”
The study, published on Tuesdaysuggests that young children who were vaccinated with most or all of the recommended aluminum-containing vaccines had at least a 36% higher risk of being 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 found in vaccines for seven of them.
Aluminum adjuvants have long been considered safe and effective. Still, scientists observed a period of rising rates of allergies and asthma among American children over a 30-year period beginning around 1980, and some wondered whether there was a connection. (These rates stabilized starting about a decade ago and have declined somewhat in recent years, for reasons that are not fully understood.)
Several previous studies found no link between aluminum-containing childhood vaccines and allergies and asthma. But other research has linked aluminum in industrial workplaces to asthma. And mice injected with aluminum 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 the risk of allergy,” said Daley, an associate professor of pediatrics at the School of Medicine at 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 about 327,000 American children born between 2008 and 2014, looking at whether they received aluminum-containing vaccines before age 2 and whether they developed persistent asthma between ages 2 and 5.
Asthma, a condition that can cause the lungs to spasm, is usually the result of an allergic reaction. About 4% of American children under the age of 5 have persistent asthma.
The researchers took measures to try to account for different factors that could influence the results, such as race and ethnicity, whether the children were born prematurely, or whether the children had food allergies or certain other conditions.
But there were many other factors they failed to address. For example, aluminum can be routinely found in breast milk, infant formula, and food, but the researchers were unable to obtain data on how much aluminum the children got from eating. They also did not have information about aluminum exposures from the air and the environment where the children lived.
The researchers split the study group in two. One was about 14,000 children who developed eczema, a skin condition that is considered 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 did not have early eczema. The other 312,000 children in the study did not have early-onset eczema.
Both groups got about the same amount of vaccine-related aluminum. The researchers found that for every milligram of aluminum received through vaccines, the risk of persistent asthma increased by 26% in children with eczema and by 19% in children who did not have eczema.
Overall, children who received 3 milligrams or more of vaccine-related aluminum had at least a 36 percent greater risk of developing persistent asthma than children who had less than 3, Daley said.
Offit said the study’s limitations meant the work “has not added anything to our understanding of vaccines and asthma.”
But other experts said the researchers drew from a respected pool of patient data and worked carefully with the best information available.
“This is public health at its finest. They’re doing everything they can to find any possible signal that might be a concern,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. . “It’s our job to look into it thoroughly to see if that’s true.”
He acknowledged that anti-vaccine activists will likely reach conclusions that the evidence does not support. But if CDC had the information and didn’t 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 School of Medicine, echoed this.
“I believe in total transparency,” he said. “If you asked a question and spent our (taxpayer) money to (research) that question, I think the results should be released in all their glory and warts.”
The Associated Press Department of Health and Science is supported by the Department of Science Education at the Howard Hughes Medical Institute. The AP is solely responsible for all content.