That’s the evidence linking autism to vaccines.

It’s also not correct to call autism an “epidemic,” as Mr. Trump often seems to do. Autism is more prevalent as a diagnosis than it used to be. But much of that in recent years is because we’ve changed the definition of what it means to have “autism spectrum disorder.” For instance, 10 years ago, two-thirds of children diagnosed with autism had below-average intelligence. But today only about a third of those diagnosed with A.S.D. do. The fastest-growing group of children with autism have average or above average intelligence. We’re being more inclusive in the diagnosis.

I am in no way minimizing the challenges facing those who have autism, or denying its prevalence. I hope my recent column discussing whether we should universally screen for autism in small children persuades you that I take A.S.D. seriously. Scaring people by claiming that autism is spreading like a disease worries them needlessly, however.

Mr. Carson, though observing there was no evidence linking vaccines to autism, also said that many pediatricians were recognizing that “we are probably giving way too many in too short a period of time.” I know of no data that supports this assertion. Pediatricians, as a group, overwhelmingly support vaccines and the current vaccine schedule.

Vaccines do not stress the human body that much. Children are continuously exposed to foreign substances that activate their immune systems. In a manuscript published in Pediatrics in 2002, Dr. Paul Offit and colleagues estimated that infants could respond to about 10,000 vaccines at any one time. The ones we give could never “use up” the immune system. It is thought that 11 vaccines at once might require the attention of about 0.1 percent of the immune system.

Moreover, it’s not the number of shots or even the number of vaccines that we should be concerned about. We should be talking about the number of antigens in the vaccines. Antigens are the molecules that spark the immune system into action. Vaccines are made to trick the immune system into developing weapons against certain antigens that are similar to the disease before having to face the disease itself.

Over time, researchers have been able to purify vaccines so that they contain fewer antigens, while still conferring immunity. They get the same results while asking less of the immune system. A single smallpox vaccine had more than 200 different antigenic proteins. In the 1980s, the seven vaccines routinely given to children contained thousands of antigens. Today, the number of antigens contained in all the vaccines given to a child by age 2 is less than 315. In contrast, it’s thought a child most likely fights off 2,000 to 6,000 antigens every day from the environment.

Yes, we’re giving more shots, but a child’s immune system has to do far less work to respond to them than in the past.