NEW YORK (AP) — A number of scientists have questioned whether aluminum, a vaccine additive that has been used for decades, plays a role in childhood allergies and asthma.
A new federally funded study has found a possible link, but experts say the study has important flaws and is no reason to change current vaccine recommendations. The study does not claim that aluminum causes the respiratory condition, and officials say more work is needed to try to confirm a link, which had not been seen in previous research.
Even if a link were ever found, the lifesaving benefits of the vaccines will likely still outweigh the asthma risk, 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 Children’s Hospital of Philadelphia, worried that the flawed study will needlessly scare some families away from proven 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 were unable to explain the effects of some potentially significant ways children are exposed to aluminum, such as in the air or through their diet.
They also noted that the findings contain inconsistencies that are hard to explain, such as why, in a subgroup of thousands of fully vaccinated children, more exposure to aluminum did not seem to result in a higher risk of asthma.
CDC officials said in a statement that it appears that aluminum-containing vaccines “do not account for the overall trends we are seeing.”
The study, released 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 produces stronger immune protection.
By age 2, children should be vaccinated against 15 diseases, according to US recommendations. Aluminum adjuvants are in vaccines for seven of them.
Aluminum adjuvants have long been considered safe and effective. Still, scientists noted a period of increased rates of allergies and asthma among American children over a 30-year period beginning around 1980, and some wondered if there was a connection. (Those percentages stabilized about a decade ago and have declined somewhat in recent years, for reasons not fully understood.)
Several previous studies found no association 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 response 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 the aluminum in vaccines could affect allergy risk,” says Daley, an associate professor of pediatrics at the University of Colorado School of Medicine.
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 the 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 staffers among the authors. This is reported by the medical journal Academic Pediatrics.
The researchers focused on about 327,000 U.S. children born between 2008 and 2014, looking at whether they received vaccines containing aluminum before age 2 and whether they developed persistent asthma between ages 2 and 5.
Asthma, a condition that can cause spasms in the lungs, is usually the result of an allergic reaction. About 4% of American children under age 5 have persistent asthma.
The researchers took steps to account for several factors that could affect the results, including race and ethnicity, whether children were born prematurely, or whether children had food allergies or certain other conditions.
But there were many other factors they could not address. For example, aluminum is routinely found in breast milk, infant formula and food, but the researchers couldn’t get data on how much aluminum the children ingested through eating. They also had no information about exposure to aluminum from the air and the environment where the children lived.
The researchers split the research group in two. One was about 14,000 children who developed eczema, a skin condition that is seen as an early indicator of the development of asthma or other allergic conditions. They wanted to see whether children with eczema were more or less sensitive to aluminum in vaccines, compared to children who did not have early eczema. The other approximately 312,000 children in the study had no onset of eczema.
Both groups received approximately the same amount of vaccine-related aluminum. The researchers found that for every milligram of aluminum received through vaccines, the risk of ongoing 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% greater risk of developing persistent asthma than children who received less than 3 milligrams, Daley said.
Offit said the study’s limitations meant the work “has added nothing to our understanding of vaccines and asthma.”
But other experts said the researchers drew from a respected set of patient data and carefully worked with the best information available.
“This is public health at its best. They are doing everything they can to find every possible signal that could 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 investigate that thoroughly to see if that’s true.”
He acknowledged that anti-vaccination activists are likely to reach conclusions that the evidence does not support. But if CDC had the information and didn’t publish it, the agency could be seen as misleading the public, further eroding trust, he said.
Dr. Sarah Long, a professor of pediatrics at Drexel University College of Medicine, echoed that.
“I believe in full transparency,” she said. “If you asked a question and spent our (taxpayer) money here to (research) that question, I think the results should be broadcast in all its warts and glory.”
The Associated Press Health & Science Department is supported by the Department of Science Education at the Howard Hughes Medical Institute. The AP is solely responsible for all content.