NEW YORK (NYTIMES) - Back in December, before the Queen of England and the president-elect of the United States had their turns, media mogul Rupert Murdoch received a dose of a Covid-19 vaccine. Afterwards, he urged everyone else to get it, too.

Since then, a different message has been a repeated refrain on the prime time shows hosted by Mr Tucker Carlson and Ms Laura Ingraham on Mr Murdoch's Fox News Channel - a message at odds with the recommendations of health experts, even as the virus' Delta variant and other mutations fuel outbreaks in areas where vaccination rates are below the national average.

Mr Carlson, Ms Ingraham and guests on their programmes have said on the air that the vaccines could be dangerous, that people are justified in refusing them and that public authorities have overstepped in their attempts to deliver them.

Mr Carlson and Ms Ingraham last week criticised a plan by the Biden administration to increase vaccinations by having healthcare workers and volunteers go door to door to try to persuade the reluctant to get shots.

"Going door-to-door?" Ingraham said. "This is creepy stuff."

Mr Carlson, the highest-rated Fox News host, with an average of 2.9 million viewers, said the Biden plan was an attempt to "force people to take medicine they don't want or need".

He called the initiative "the greatest scandal in my lifetime, by far".

Mr Carlson's guest on that episode, veteran Fox News political analyst Brit Hume, pushed back slightly, saying, "What they're trying to do is make it as easy as possible for people to get the vaccine and, for people who are hesitant, to perhaps encourage them that they have nothing to fear."

Mr Hume was quick to add that "vaccines do have side effects" and said those who are hesitant "should be respected".

Opposition to vaccines was once relegated to the fringes of American politics, and the rhetoric on Fox News has coincided with efforts by right-wing extremists to bash vaccination efforts.

Served up to an audience that is more likely than the general population to be wary of Covid-19 vaccines, the remarks by Mr Carlson and Ms Ingraham echoed a now-common conservative talking point: That the government-led effort to raise vaccination rates amounted to a violation of civil liberties and a waste of taxpayer dollars.

The comments by the Fox News hosts and their guests may have also helped cement vaccine scepticism in the conservative mainstream, even as the Biden administration's campaign to inoculate the public is running into resistance in many parts of the country.

Public health experts have said that a strong vaccination effort is critical for the US to outrun the virus, which has killed more than four million people worldwide and continues to mutate.

The amplification of vaccine scepticism through conservative media channels could harden the reluctance of those who might otherwise have been persuaded to get a shot, said Dr Kathleen Hall Jamieson, a communications professor at the University of Pennsylvania.

"If you have constant exposure to an outlet that is raising vaccination hesitancy, raising questions about vaccinations, that is something to anchor you in your position that says, 'I'm not going to take the vaccine,' " Dr Jamieson said.

A Fox News spokesman provided past statements by Mr Carlson voicing his general support for vaccines. "I've had a million vaccines in my life, as we all have," the host said on an April show. "I think vaccines are great." The spokesman also noted that Ingraham had spoken in favour of adults choosing to receive vaccines if they wanted them.

White House officials said Thursday (July 8) that virtually all new coronavirus hospitalisations and deaths nationwide involved unvaccinated people. The five states with the worst outbreaks as at Wednesday had below-average vaccination rates; four of them voted for former president Donald Trump in last year's election.

Vaccine resistance was greater among Republicans than Democrats, according to an April study by the Public Religion Research Institute. Among Republicans who watch Fox News, 45 per cent said they were hesitant or unwilling to get a Covid-19 shot, compared with 68 per cent of viewers who watch the niche right-wing news channels Newsmax or One America News Network.

Mr Carlson has had the unshakable support of his bosses. In a May interview with Insider, Mr Murdoch's elder son Lachlan, who runs Fox News with his father, defended Mr Carlson against his critics and called him "brave".

As at July 4, 67 per cent of American adults had received at least one shot, just short of US President Joe Biden's goal of 70 per cent. Media campaigns to increase vaccination rates, such as public service announcements from the non-profit Ad Council, have been addressed to hesitant Americans.

While two of Fox News' prominent hosts and their guests have questioned vaccination efforts, the channel has also produced its own vaccine public service announcement, a 30-second spot featuring hosts and anchors Steve Doocy, Harris Faulkner, Dana Perino and John Roberts. "If you can, get the vaccine," Ms Faulkner says in the ad.

Fox News chief political anchor Bret Baier said in an Instagram post that he was "grateful" for the shot. In May, the hosts of "Fox & Friends" spoke on-air of their "relief" at getting vaccinated. And Ms Faulkner hosted a prime-time special in February that sought in part to "debunk common myths" about the vaccine.

Prime-time Fox News host Sean Hannity, who fell behind Mr Carlson in the ratings race during the Trump years, said on a May episode of "Hannity" that he had received a Covid-19 shot. "I do believe in science, and I believe in vaccinations," he said. "Talk to your doctor," he continued. "You don't need to talk to people on TV and radio that aren't doctors."

Ms Ingraham has been more skeptical. Last week she accused the news media of overhyping the threat of Covid-19 to children and often refusing to discuss adverse reactions linked to the vaccines, although such outcomes have been covered by The New York Times, The Washington Post, CNN and other outlets.

Fox News is not the only outlet that has been critical of vaccine efforts. Newsmax covered Mr Biden's outreach plan on its website with the headline "Biden Blasted for 'Sick' Door-to-Door Vaccine Campaign"; One America News Network greeted the proposal with the headline "Joe Biden to Send Operatives to Harass Americans Into Taking Covid-19 Vaccines".

Dr Joshua Sharfstein, a public health professor at Johns Hopkins, called the rhetoric against vaccine campaigns "a terrible development".

"We have such strong political opinions in this country," he said, "and if people associate their political identity with a position on a public intervention, it's very hard to penetrate that with good information."

The remarks against vaccination efforts on "Tucker Carlson Tonight" and "The Ingraham Angle" have come during a ratings resurgence for Fox News.

For years, Mr Murdoch's channel was the ratings leader among cable news networks - only to fall behind CNN in the wake of the 2020 election, when Fox News was the first news organisation to project Mr Biden as the winner of Arizona, a key swing state.

Newsmax, which was more frankly pro-Trump in its coverage, gained viewers in the weeks after election day. At the same time, One America News accused Fox News of joining "the mainstream media" in an effort to recruit the channel's disaffected fans.

Now the old ratings order has been restored: Fox News finished far ahead of its main rivals, CNN and MSNBC, with an average of nearly 2.2 million viewers during prime time in the second quarter of this year, according to Nielsen ratings.

Its return to the top came thanks, in part, to a programming strategy that gave more hours per week to opinion shows rather than news broadcasts. And as it climbed back to ratings dominance, two of its commentators - Ms Donna Brazile, a former Democratic Party chair, and Mr Juan Williams, a moderate - left the network. Both had served as foils to the channel's conservative pundits.

In a recent opinion essay for The Daily Beast, Mr Preston Padden, a former high-level executive at Fox Broadcasting, wrote that Fox News had "contributed substantially and directly" to "the unnecessary deaths of many Americans by fuelling hesitation and doubt about the efficacy and safety of lifesaving Covid-19 vaccines". He singled out the channel's prime-time opinion programmes for blame.