NEW YORK (AP) – Many scientists have suspected that aluminum, a vaccine additive 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 study has important weaknesses and is not a reason to change current vaccination recommendations. The study doesn’t show that aluminum causes respiratory problems, and officials said more work is needed to confirm any link that hasn’t been seen in previous studies.

Even if a link is found, the vaccine’s life-saving benefits may still outweigh the risk of developing asthma, said study leader Dr. Matthew Daly. But if the results are confirmed, it could create new work to redesign vaccines, he said.

Dr. Paul Offitt, of the Children’s Hospital of Philadelphia, worries that the flawed study will scare some families away from proven vaccines.

“Making an extraordinary claim requires extraordinary evidence,” Offit said. This study does not provide such evidence, he said.

He and other outside experts pointed out that Daley and his colleagues were unable to identify the effects of some of the potentially important ways in which children are exposed to aluminum — such as through the air or through their diet.

They also point out that the findings include inconsistencies that are difficult to explain, including why, among thousands of fully vaccinated children, additional aluminum exposure does not seem to increase the risk of asthma.

CDC officials said in a statement that aluminum-containing vaccines “do not account for the overall trends we are seeing.”

The study, It was released on TuesdayIt suggests that young children who were vaccinated with most or all of the recommended aluminum-containing vaccines were at least 36% less likely to develop 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 induces a strong immune response.

At the age of 2, children should be vaccinated against 15 diseases, according to American recommendations. Aluminum supplements are available in vaccines for seven.

Aluminum supplements are considered safe and effective for a long time. Still, scientists have pointed to an increase in rates of allergies and asthma in American children in the 30 years since about 1980, and some have questioned whether there is a connection. (Those rates started about a decade ago and have declined somewhat in recent years, for reasons that are not fully understood.)

Several previous studies have found no link between aluminum-containing childhood vaccines and allergies and asthma. But other studies have linked aluminum in industrial workplaces to asthma. And mice injected with aluminum suffer an immune system response that causes airway inflammation of the type seen in childhood asthma.

“Given the limited animal data, there is a theoretical concern that aluminum in vaccines may affect the risk of allergic reactions,” said Daley, an associate professor of pediatrics at the University of Colorado School of Medicine.

In the year 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, Daly said. It is funded by the CDC and includes current and former CDC staff among its authors. Published in Academic Pediatrics Medical Journal.

The researchers focused on 327,000 US children born between 2008 and 2014, whether they received aluminum-containing vaccines before age 2 and whether they had persistent asthma between age 2 and 5.

Asthma, a condition that can cause spasm in the lungs, is usually an allergic reaction. About 4% of children under the age of 5 have persistent asthma.

The researchers took measures to account for various factors that could have influenced the results, including race and ethnicity, whether the babies were born prematurely or whether the babies had food allergies or other conditions.

But there were many other things they could not solve. For example, aluminum is normally found in breast milk, infant formula and food, but the researchers were unable to find out how much aluminum the children received. In addition, the children did not have any information about aluminum exposure from the air and environment where they live.

The researchers split the study group into two. One is that about 14,000 children develop eczema, a skin condition that can be seen as an 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 without early eczema. The other 312,000 or so children in the study did not have early eczema.

Both groups received approximately the same amount of vaccine-associated aluminum. The researchers found that for every milligram of aluminum in the vaccine, the risk of persistent asthma increased by 26 percent in children with eczema and 19 percent in children without eczema.

Overall, children who received 3 milligrams or more of vaccine-related aluminum were 36 percent more likely to develop persistent asthma than children younger than age 36, Daley said.

A limitation of the study, Offit said, is that the work “doesn’t add anything to our understanding of vaccines and asthma.”

But other experts say the researchers worked carefully with a respected patient data set and the best available data.

“This is public health at its best. Michael Osterholm, director of the Minnesota Center for Infectious Disease Research, is doing his best to find signs of concern. It’s our job to dig deep into that to make sure it’s true.

Anti-vaccination activists admit that they may conclude that the evidence does not support it. But if the CDC has the information and doesn’t publish it, the agency could be seen as misleading the public and further eroding trust, he said.

Dr. Sarah Long, professor of pediatrics at Drexel University College of Medicine, echoed this.

“I believe in absolute transparency,” she said. “If you ask an inquiry and spend our (taxpayer) money here on the inquiry (to investigate), I think the result should be seen in all its warts and glory.”

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