Bill Ackman said in 2021 that delaying Covid vaccinations for older Americans “seems like genocide.”

Today, the influential hedge fund chief and investor is amplifying the debunked anti-vaccine views of Democratic presidential candidate Robert F. Kennedy Jr.

Ackman is not denying his change. In fact, he said Kennedy is asking “important questions” about vaccines, raising issues he is interested in learning more about.

Several of Ackman’s recent tweets about Covid vaccines have stunned and confounded many of his colleagues on Wall Street, according to several people who have known and been allied with him for years. And it’s led both his allies and foes to ask the same question: Why is he doing this?

Ackman answered that question in an interview with CNBC on Wednesday.

“I listened to RFK on several podcasts and a town hall and thought he raised important issues about vaccines and other issues that were worth learning more about,” said Ackman, the CEO of Pershing Square Capital. “I don’t feel like we’ve fully answered questions about the safety of all vaccines, particularly more recently approved vaccines, and our approach to determining their safety and efficacy.” 

Although the effectiveness of the Covid vaccines has declined over time as the virus has evolved into new variants, public health officials say the shots are a critical tool in preventing hospitalization and death from the virus, particularly among the elderly and people with pre-existing medical conditions. Serious side effects are rare. The CDC and FDA closely watch vaccine safety though large monitoring systems, and regularly discuss any issues at public advisory committee meetings.

Ackman, a billionaire whose commentary can move markets, is the latest high profile executive to show support for Kennedy and his opinions. 

Wall Street veteran Omeed Malik is hosting a campaign fundraiser for Kennedy later this month in the Hamptons. Venture capitalist David Sacks and fellow tech leader Chamath Palihapitiya hosted a fundraiser for Kennedy in June, which raised approximately $500,000 for Kennedy’s campaign. Ackman would not say whether he planned to donate to Kennedy’s campaign for president.

Ackman’s new stance on vaccines marks a dramatic shift for the investor. In 2021, he said the U.S. should “launch mass vaccinations” of the elderly. He reaped large profits during the peak of the Covid pandemic, by selling his bets against the market, just days after warning on CNBC that “hell is coming” and imploring the Trump White House to shut down the country for a month. Ackman, in a March 26 letter to investors, called the idea that his comments moved the market “absurd.” “Beginning on March 12th, we began unwinding our hedge, and continued to do so every day thereafter until we completed our exit on the morning of March 23rd,” he wrote.

Ackman told CNBC his newfound worries about vaccines come from being a parent and a concerned citizen. He said Kennedy, in his view, is asking “important questions” about them. “Unfortunately, vaccines are not safety tested,” Kennedy said at a town hall late last month.

Scientific researchers and medical officials have emphatically rejected Kennedy’s stances on vaccines, including his earlier argument that vaccines can lead to autism.

Ackman has pushed his newfound skepticism to his approximately 740,000 followers while saying he is not opposed to vaccines. He has also taken on a doctor who is known for pushing back on misinformation related to Covid.

“@RobertKennedyJr and others have raised important questions about the safety of some vaccines and have sought explanations for the dramatic increases in the incidence of childhood allergies, autism, and other health issues. These are good questions that have not been adequately answered,” Ackman said in a tweet last month that quoted a video of former Fox News host Tucker Carlson arguing that Kennedy is getting the better of President Joe Biden in the early days of the Democratic primary campaign.

Biden enjoys a substantial lead in Democratic primary polls, although Kennedy is pulling double-digit support.

When asked if he believes whether Kennedy should be president, Ackman said: “I don’t yet know, but I think he is asking important questions and raising interesting issues that are worthy of discussion and debate.”

Ackman, who has backed Democrats in the past, also wouldn’t say whether he will back Biden.

“It depends on the alternatives at the time of the general election,” Ackman said. “My strong preference is that he announces now that he won’t run to create a more open field for other candidates.”

Some say Ackman could be positioning himself to have more influence in politics, including possibly running for office one day. Ackman said in a recent tweet that he planned to meet with Schumer this week to discuss his idea of how to fix the college student debt problem after the Supreme Court struck down Biden’s relief plan.

Ackman denied having any plans to run for office and declined to comment about the Schumer meeting.

Others say he could be trying to align himself with outspoken business leaders who are more conservative and have been echoing similar takes, such as Sacks and Twitter owner Elon Musk. Sacks and Musk have both expressed support for Kennedy and GOP presidential candidate Ron DeSantis, the governor of Florida.

Many of those familiar with Ackman – allies and rivals alike – talked to CNBC on the condition of anonymity in order to openly speak about their stances on why they believe he has suddenly trained his contrarianism on issues like vaccines and Russia.

Carl Icahn, the veteran activist investor and a longtime adversary of Ackman’s, told CNBC in a phone interview that he believes the Pershing Square CEO’s tweets are yet another example of how wrong Ackman can be.

“His tweeting might be a positive. Since I’ve known him, he’s almost never been correct about anything he’s said. Therefore if one reads his tweets, and does the opposite, you’re almost sure to be correct and very possibly make a large profit,” Icahn said.

“He makes large bets and like the riverboat gambler, he does win sometimes but often loses hugely. Just look at the billions he’s lost in Herbalife and Valeant. Most riverboat gamblers die broke,” Icahn said. “The only difference between him and a riverboat gambler is not only he’s losing his own money, unfortunately he’s losing a lot of other people’s money, too.”

Ackman declined to comment on Icahn’s remarks.

Institutional Investor reported Ackman broke a three-year winning streak in 2022, registering his first down year since 2018. Pershing Square Holdings fell more than 8% for the year, according to the publication.

Ackman’s recent tweets have turned heads beyond Wall Street, too. Alexander Reid Ross, a disinformation expert who lectures at Portland State University in Oregon, told CNBC that it appears Ackman is going back and forth on different conspiracies – and getting things wrong.

Reid Ross pointed to Ackman’s latest tweets pertaining to the Wagner Group’s armed rebellion in Russia.

“Ackman’s profile seems to veer wildly and be attracted to statements that may seem interesting and extreme but end up wrong. For instance, on the latest Wagner rebellion, he shares one person saying in effect ‘either [Vladimir] Putin kills Prigo [Yevgeny Prigozhin] or Moscow falls,’ and in another case he supports the nation that Putin made the whole thing up,” Reid Ross said. “This is veering wildly from one false assumption to the next one, both of which being mutually exclusive.”

As he apparently defended Kennedy’s broadly debunked and criticized stances on vaccines, Ackman also injected himself into a Twitter battle involving Dr. Peter Jay Hotez, who has pushed back on misinformation related to the coronavirus and vaccines. 

Podcast host Joe Rogan initially pushed the idea of having Hotez and Kennedy debate. Rogan, who has made his popular show a platform for celebrities as well as conspiracy theorists, offered to give $100,000 to a charity if the doctor was willing to come on his show to debate Kennedy. Ackman later said he would “add $150,000 to @joerogan’s wager so now $250,000 can go to charity and the public can hear an open debate on an important topic.”

Musk chimed in and said “Maybe @PeterHotez just hates charity.” Hotez refused to debate Kennedy but did say he was willing to go on Rogan’s show to discuss his own position on vaccines. He later said on Twitter that “a couple of antivaxers” showed up at his private residence in Texas “taunting” him to debate Kennedy.

At first, Ackman encouraged a debate between Kennedy and Hotez. Later, he walked back the idea and criticized the doctor, who says on his website that he worked in the “development of coronavirus vaccines including vaccines administered to over 100 million people in India and Indonesia.”

“Based on my further research Hotez does not appear to be a credible advocate for vaccine policy in light of the repeated inaccuracies of his public statements during the crisis and potential conflicts he may have,” Ackman tweeted to his more than 700,000 followers on June 19.

Hotez responded to Ackman on Twitter the next day.

“Awful to read Mr. Ackman’s account of my activities. I have no pharma conflicts, I co-developed low-cost patent-free Covid vaccines for global health reaching 100 million doses. I never took a cent for any cable news/podcast/radio appearances,” Hotez said.

“And you have the audacity to present phony conspiracy websites that monetize the internet as your evidence?”

— CNBC’s Lora Kolodny contributed to this report.