Things are getting down and dirty now. And millions of lives are at stake. I cannot possibly state strongly enough how dangerous it is that President-elect Donald Trump has embraced the notion that vaccination is the cause of autism.

Robert F. Kennedy Jr., a celebrated vaccine skeptic, met with Trump on Jan. 10. Speaking to reporters outside Trump Tower in Manhattan after the meeting, Kennedy said he will chair a commission “on vaccine safety and scientific integrity” at Trump’s request, because, “we ought to be debating the science.”

(One news organization, the Guardian, later reported that the Trump team denies Kennedy will lead such a commission, but offered no explanation for why the environmentalist was summoned to meet with the president-elect.)

Kennedy has long held the position that vaccines are dangerous, and that the measles-mumps-rubella (MMR) vaccine administered to American children is a likely cause of autism. Like any good conspiracy theorist, Trump has long questioned the wisdom of vaccines. On Oct. 22, 2012, he tweeted that vaccines constitute “doctor-inflicted autism.”

In August 2016, Trump met with the disgraced ex-physician, Andrew Wakefield, who originated the claim. Formerly a gastroenterologist, Wakefield conducted experiments on children that he claimed proved they acquired autism from MMR immunization. The research was published in the British medical journal Lancet in 1998 but was retracted in 2010 by the journal, which stated: “ … claims in the original paper … have been proven to be false. Therefore we fully retract this paper from the published record.”

Wakefield’s license to practice medicine in the United Kingdom was stripped for “serious misconduct.” The British Medical Jjournal went even further, denouncing Wakefield’s work as “fraudulent.” Before the investigation was completed, Wakefield relocated to Austin, Texas, where he continues to lead vaccine opposition.

Wakefield produced a documentary, “Vaxxed,” in which he defends his work and claims to be the victim of a vast conspiracy. His defenders adhere to the conspiracy idea, insisting that the Centers for Disease Control and Prevention, the entire global vaccine industry, the World Health Organization, the National Institutes of Health, the pharmaceutical industry, and all the major science and medical journals in the world are joined in the mission of inflicting autism through vaccines.

So let’s get a few things straight.

Yes, there has been an increase in autism diagnoses in parts of Europe, the United States and Canada — but this is largely because psychiatric associations have widened the definition of the disorder, now describing autism as a spectrum that ranges from the extreme of complete nonfunctionality all the way to socially challenged genius, or Asperger’s syndrome. Some additional rise in rates may not be fully explained by the expanded diagnostic definition: It is likely that parent and physician awareness, coupled with lowered stigma, has brought more cases to light. Boys are at least five times more likely to be diagnosed with autism spectrum disorder than girls, yet the genders are equally likely to be vaccinated.

Mr. Trump, back in the day when you and I were children and were vaccinated — thankfully — to prevent us from getting measles, rubella, polio, diphtheria, tetanus and other awful diseases, a mercury-based preservative was used to keep vaccines from going bad on doctors’ shelves. Kennedy claims the mercury is still used as a preservative and causes brain damage. But the American Academy of Pediatrics and the Food and Drug Administration removed thimerosal, the preservative in question, from vaccines and it has not been used in MMR since 1999.

Given Trump’s interest in Russia, he might be interested to know that the first claims of an association among vaccines, mercury and child neurological health problems were raised in the early 1980s by Soviet virologist Galena Petrovna Chervonskaya and trumpeted in the Communist Party’s newspaper, Komsomolskaya Pravda. Vaccination rates fell so low following the report that Soviet soldiers returning from war in Afghanistan, where diphtheria was still common, unwittingly spawned an epidemic that swept the Soviet Union, causing the worst outbreak since World War II. Some 200,000 unvaccinated children contracted diphtheria, which killed roughly 2 to 3 percent of those infected, varying by region.

Vaccines save lives. Back in 1970, when measles was the No. 1 cause of death for African children under 5, most of the continent’s nations had child mortality rates around 400 per 1,000 live births, meaning nearly half the toddlers wouldn’t survive to celebrate their fifth birthday. I bitterly recall walking through pediatric wards in northern Tanzania in 1983, filled to capacity with tiny children covered in measles rash, fighting for their lives.

Today that horror has plummeted, thanks to UNICEF, GAVI, the Bill & Melinda Gates Foundation, WHO and hundreds of nongovernmental organizations around the world that have brought the power of immunization to the poorest and most remote parts of the planet. And, if worldwide contributions to vaccine efforts stay on course, the combined impact of all immunizations from 2011 to 2020 will be 23.3 million lives saved, most of them babies.

Trump should know that the most virulent anti-vaccine force on Earth is the Taliban, which has executed, bombed, kidnapped and maimed about 10 times more polio vaccinators in Pakistan and Afghanistan since 2005 than there are children who have contracted polio. In Nigeria, Boko Haram has blocked immunizers and spawned outbreaks of polio and measles. Thanks to the Syrian war and massive disruptions of family lives across the Middle East, polio has returned, measles has erupted, and millions of dollars’ worth of special vaccination campaigns are underway in refugee camps and war-torn parts of Syria and Yemen.