Washington — GOP Sen. Bill Cassidy of Louisiana on Sunday urged the president to be “radically honest” when he’s speaking about vaccines, as the U.S. this year has recorded the most measles cases in more than three decades.

“I would just ask the president to be aware that people are listening to him — if he discourages immunization, there’ll be fewer people immunized, and if we’re speaking of measles, there’ll be more people sick in the hospital or even die,” Cassidy said on “Face the Nation with Margaret Brennan.”

The Trump administration has been encouraging parents to vaccinate their children against measles in recent months, as cases have climbed. But Mr. Trump has cast doubt on the vaccine and its schedule, including through an executive order last month suggesting that the measles, mumps and rubella vaccine, known as MMR, should be given as three separate shots. He also claimed without evidence that the MMR vaccine, if not separated, could be “lethal.” 

Speaking to reporters in the Oval Office on Friday, the president said he is going to “demand” that drug companies split up kids’ vaccines into five doses, given in six-month intervals. He said, “the vaccine size will be much, much less” and argued that it will lead “to a massive reduction in autism.”

“So instead of having a massive dose of 82 or 88 different vaccines pumped into your arm, we’ll take out certain vaccines that people are a little worried about,” Mr. Trump said. 

Cassidy, a medical doctor, said he didn’t know which vaccines the president was referencing. But he stressed that there needs to be “radical honesty.”

“Have the president come forward — what is he basing this on? Who’s giving him advice?” Cassidy said. 

Cassidy said he approaches the issue “as a physician,” saying people are worried, and “we need to address that worry where it is.”

“If you want to be radically honest, the vaccines are safe, they’ve been proven to be safe, and the current regimen has been timed to be most convenient to the parent,” he said. “At any point, the parent can say, ‘I want something different.'”

Cassidy urged the president to explain his position, asking, “Why do you think this vaccine is lethal?”

“Have you ever seen a case of lethality?” he said. “And what about the people who are not vaccinated, who are getting sick and even dying?”

The Louisiana Republican cited recent measles-related deaths, including a 40-year-old and an 18-year-old. He said, “having measles is not a kind of victimless kind of experience,” comparing it to drunk driving. 

“You can drink and get drunk, but if you drive, you’re going to hurt other people,” Cassidy said. “You can get measles, but when you start spreading it to other people, a 40-year-old dies, an 18-year-old dies, children in a neonatal intensive care unit are at risk. People have got to realize, and the government has to realize it. The president should be saying, ‘Be vaccinated. It is safe and effective.'”

He added, “We should have a common voice of radical honesty, of trying to help the American people understand what is safe. And if the president calls it lethal, then where are you getting your information, Mr. President? And if you really don’t have it, why are you willing to risk the lives of fellow Americans?”

The Louisiana Republican, who’s leaving office early next year after the president endorsed his GOP challenger, chairs the Senate Health, Education, Labor and Pensions Committee. Asked what he needs to hear from the nominee for FDA commissioner, Heidi Overton, at her hearing this week, Cassidy said, “I need to hear that she understands that calling the measles vaccine lethal is absurd, and we need radical honesty.”

Cassidy also noted that the president’s nominee for surgeon general, Nicole Saphier, said in a committee hearing last week that the MMR vaccine is not lethal, while encouraging people to get vaccinated. Cassidy said she earned his vote. 

“When somebody is willing to be honest to the American people and say that vaccines are safe, you should be taking it, and the consequence of not can even include death, well, what else can you ask for when it comes to vaccines?” he said.