At Robert F. Kennedy Jr.’s confirmation hearings, beginning on Wednesday, senators are expected to question him closely about his controversial views on vaccines.

For years Mr. Kennedy has questioned the safety of vaccines, including those for polio and measles, two diseases that continue to harm children. More recently, he has said that he’s not planning to take vaccines away from Americans but wants to release safety data to the public — even though nearly all of the data is already publicly available.

Mr. Kennedy’s contrarian views extend well beyond vaccines. And as secretary of health and human services, he would have enormous influence on health policy, even on issues typically under state control, by cutting funding for certain programs or elevating others.

Here’s a fact check of some of his claims.

This is false. Mr. Kennedy’s number is off by orders of magnitude.

The National Diabetes Statistics Report estimated that in 2021, about 35 per 10,000 children and adolescents younger than 20 — that is, 0.35 percent — had a diagnosis of diabetes. Another study found that 0.1 percent of young people 10 to 19 had diabetes in 2017.

Mr. Kennedy also seems to be conflating juvenile or Type 1 diabetes, an autoimmune disease, with Type 2 diabetes, which can result from an unhealthy lifestyle. He is correct that new cases of diabetes — both types — are on the rise. But the prevalence in teenagers is still much lower than in adults and increases with age; the highest prevalence, 29.2 percent, is among adults 65 and older.

In a later comment that included prediabetes, Mr. Kennedy said, “These kids are now dependent on, you know, insulin and diabetes treatments, on chronic disease treatments for the rest of their lives, and that’s bankrupting our health care system.”

While prediabetes is a warning sign for diabetes, most cases don’t require treatment with insulin and can be reversed with lifestyle changes, including modest weight loss. Prediabetes, too, is rising; about 28 percent of teenagers are prediabetic.

This is false. Every year, scientists track the effectiveness of the annual flu vaccine. And every year, dozens of studies document the vaccine’s effectiveness against hospitalizations and deaths. The exact numbers vary, but the results always show that vaccination is beneficial.

Injected flu vaccines do not contain live virus, and nasal spray vaccines contain weakened virus; neither type can transmit the flu.

The flu vaccine’s composition is typically determined in the spring, based on the dominant variants in the Southern Hemisphere at that time. In some years the vaccine that is produced is an excellent match for the viruses that emerge in the fall, and in other years the scientists’ best guess is a little off.

As a result, effectiveness may range from 30 to 90 percent, depending on the age group and the subtype of influenza. But even when effectiveness is low, the vaccine can shorten the duration and severity of illness.

Because flu tends to be most severe in children under 5 and in older adults, the vaccine is particularly recommended — not mandated — for those age groups. And since the flu vaccine was introduced in 1945, life expectancy, including among older adults, has risen steadily.

This needs context. Mr. Kennedy is partly right. One in 36 American children is diagnosed with autism spectrum disorder, according to the Centers for Disease Control and Prevention (the one-in-34 estimate is specific to boys). And in California, one in 22 children has autism.

But autism is a spectrum, and a majority of those diagnosed can participate in sports, write poetry (if they are so inclined), pay taxes, date and marry; many are parents. The list of people with autism includes successful athletes, writers, actors, activists, artists, politicians — and even Elon Musk, the richest man in the world and head of the Trump administration’s government cost-cutting effort.

Studies suggest that most of the increase in autism diagnoses is on the milder end of the spectrum, in part because the diagnostic criteria have widened.

What Mr. Kennedy describes is a subset of autistic people, about one in four with the diagnosis, who are profoundly affected. But even they are more likely to harm themselves than others. (The prevalence of profound autism is rising, but slowly.)

Mr. Kennedy may not have seen such people when he was a child because back then, most of them were isolated at home or institutionalized, misdiagnosed with mental illnesses and heavily medicated.

This needs context. First, most states mandate that children receive about 20 shots to enter school, but those shots include doses of eight or so vaccines (depending on which combination vaccines are used) that together protect against a dozen diseases.

Even including vaccines that are recommended and not required, such as a yearly flu shot, children may receive 35 shots by age 5. Mr. Kennedy’s math would be correct only if the number included vaccines given in pregnancy, and if each component and each dose of a combination product were considered a separate vaccine.

All vaccines must meet strict requirements for safety before approval. Even after their approval, federal officials monitor reports of side effects in multiple systems that analyze medical records and reports from patients and doctors.

Mr. Kennedy’s claim that none of the shots have been tested in placebo-controlled trials also needs context. Some of the vaccines currently in use have indeed been tested against a placebo; others are newer alternatives to vaccines that underwent placebo-controlled trials before approval.

A newer vaccine is often tested against an approved one — rather than against a placebo — to show that it is just as good at preventing disease. Newer treatments for certain diseases like cancer are similarly tested in such trials, which are called non-inferiority trials.

That’s because it would be unethical to deny some children in a trial protection against a dangerous pathogen, as it would be to deny treatment to patients with a disease, by giving them a placebo.

This is false. Numerous studies have examined this claim and found it to be unsubstantiated. On the contrary, pertussis itself, rather than the vaccine, can be dangerous or even fatal to young children.

In both statements, Mr. Kennedy is referring to a vaccine for pertussis, or whooping cough, that was discontinued in the 1990s. The vaccine was made from inactivated bacteria and, compared with the newer vaccines, was associated with more side effects, including fever, drowsiness and irritability.

But research has not found severe short- or long-term consequences. According to one large study, for every 100,000 doses of the vaccine, fewer than nine produced a febrile seizure on the day of vaccination.

Febrile seizures are seizures caused by high fevers and can occur during any childhood illness, including an ear infection; they do not cause lasting harm. Longer-term follow-ups by several teams have shown no evidence of brain damage in children who received the vaccine.

Mr. Kennedy is correct that one team reported increased mortality after pertussis vaccination in West Africa. But a series of independent panels that was convened to examine the studies unanimously concluded that the team’s data did not support this conclusion.

“Indeed, the papers provide substantial evidence against such a conclusion,” the experts wrote.