For more than 20 years, the Centers for Disease Control and Prevention told the public that studies show no link between vaccines and autism. On Nov. 19, it revised its messaging, acknowledging that current evidence does not rule out a possible association. This was not an announcement of a newly discovered risk; it was a correction of an earlier claim that exceeded what the science had demonstrated. The CDC update to its website was a long-overdue correction of the messaging.
The reality of the research on autism and vaccines is clear. All the foundational studies on this topic — the ones cited to say that the science is settled — were designed to detect moderate to large increases in the risk of autism. None of them were designed to detect small increases, and by “small” think increases in autism risk of 5% to 20%.
When researchers claimed there was “no detected association,” that careful framing was correct. When the CDC and other public health authorities extrapolated this to suggest there was no possible association, that was wrong. There are about 3.5 million children born each year in the United States. A “small” increase would translate into thousands of additional autism cases, yet those real children would be statistically invisible. An association too small for a study to detect is not the same as an association that does not exist.
Since the National Childhood Vaccine Injury Act of 1986, there has been an explosion in the U.S. vaccine schedule, which now contains a volume of vaccines — and correspondingly high aluminum exposure — without comparison in most of the developed world. While each individual modern vaccine contains fewer antigens than older forms, children now receive far more distinct vaccines, generating more overall immune activation than earlier generations.
No major study, not one, has evaluated autism risk under this combined exposure profile: more vaccines, more immune stimulation, and more aluminum delivered earlier in life than in virtually any peer nation. While we have intensified the U.S. vaccine schedule, the studies used to dismiss concerns about autism risk have come from populations that have experienced nothing even close to the exposure levels most American infants face.
More research is needed. The available evidence on aluminum toxicity calls out two areas of special concern: inflammatory diseases, such as asthma, are the canary in the coal mine for the harms aluminum exposure can cause, but neurodevelopmental injury is not far behind in animal studies. The CDC’s own study on vaccine-aluminum exposures in U.S. children did find a statistically significant association for the development of asthma. Crucially, this same well-constructed U.S. cohort data has never been analyzed for neurodevelopmental outcomes.
For too long, our messaging on vaccines and autism overstated the evidence. The CDC focused on population-level vaccine safety, and when families reported observing abrupt developmental changes immediately following vaccination, it denied any possibility of an association; it gaslit them. These reports never proved causation, but dismissing them outright created predictable mistrust. Parents were never persuaded.
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The CDC’s updated language is not a retreat from vaccines; it is a return to scientific precision. The evidence has not found a link between vaccines and autism, but it has never been studied in a way that would be capable of establishing one. With today’s tools and a willingness to revisit earlier CDC research, we have the opportunity to start asking the questions that need to be answered and produce studies that actually investigate the impact of all the vaccines in the current schedule.
Rebuilding trust begins with aligning public statements with actual evidence. The change the CDC made is an important step in the right direction.
Monique Yohanan, MD, MPH, is a senior fellow for health policy at Independent Women.
