President Biden’s surgeon general on Thursday used his first formal advisory to the United States to warn against the dangers of health misinformation, calling it an “urgent threat to public health” and urging all Americans — and specifically tech and social media companies — to do more to curb the spread of falsehoods about Covid-19.

The official warning by Dr. Vivek Murthy is unusual; surgeons general have traditionally used their official “advisories” — short statements that call the American people’s attention to a public health issue and provide recommendations for how it can be addressed — to talk about health matters ranging from tobacco use to opioid addiction, suicide prevention and breastfeeding.

But this new advisory, contained in a 22-page report with footnotes, occurs in a more political context. Fox News hosts like Tucker Carlson and Laura Ingraham, along with their guests, are among those who have been casting doubt on Covid-19 vaccines, which studies show are highly effective at preventing death and hospitalization from the disease.

Health misinformation about social distancing, mask use, treatments and vaccines has been rampant during the coronavirus pandemic. The report is a sign that the Biden administration, faced with a steep decline in vaccination rates, is moving more forcefully to confront it. Fewer than 50 percent of Americans are fully vaccinated, and many top health experts have called for the president to do more to reach people who have yet to be get shots.

While virus numbers remain at some of the lowest levels since the beginning of the pandemic, they are once again slowly rising, fueled by the spread of the more contagious Delta variant; vaccines are effective against the variant. Counties that voted for Mr. Biden average higher vaccination levels than those that voted for Donald Trump. Conservatives tend to decline vaccination far more often than Democrats.

“Health misinformation is a serious threat to public health,” Dr. Murthy said in the report. “It can cause confusion, sow mistrust, harm people’s health, and undermine public health efforts.”

In a statement, he added, “From the tech and social media companies who must do more to address the spread on their platforms, to all of us identifying and avoiding sharing misinformation, tackling this challenge will require an all-of-society approach, but it is critical for the long-term health of our nation.”

But calling out tech and media companies is tricky business, and the White House has danced around the question of whether it would try to regulate companies like Facebook that have become platforms for health disinformation. Asked about this at her Wednesday briefing, the White House press secretary, Jen Psaki, was noncommittal.

“Obviously, decisions to regulate or hold to account any platform would certainly be a policy decision,” she said. “But in the interim, we’re going to continue to call out disinformation and call out where that information travels.”

The report is assiduously apolitical, and does not name any specific purveyors of misinformation. But it comes as some Republican leaders, concerned that the virus is spreading quickly through conservative swaths of the country, are beginning to promote vaccination and speak out against media figures and elected officials who are casting doubt on vaccines.

Health misinformation is not a recent phenomenon — and is not limited to news media. In the 1990s, the report notes, “a poorly designed study” — later retracted — falsely claimed the measles, mumps, rubella vaccine causes autism.

“Even after the retraction, the claim gained some traction and contributed to lower immunization rates over the next twenty years,” the report said.

Dr. Murthy is expected at Thursday’s White House briefing to discuss his report. It cites evidence of the spread of misinformation, including a study by the Kaiser Family Foundation that found, as of late May, that 67 percent of unvaccinated adults had heard at least one Covid-19 vaccine myth and either believed it to be true or were unsure of its truthfulness; and a Science Magazine analysis of millions of social media posts found that false news stories were 70 percent more likely to be shared than true stories.

Another recent study showed that even brief exposure to misinformation made people less likely to want a Covid-19 vaccine, the surgeon general said.

This is Dr. Murthy’s second turn at being surgeon general; he also served under former President Barack Obama. The position, often referred to as the “nation’s doctor,” offers little formal policymaking authority, but derives its strength from the surgeon general’s bully pulpit, and past surgeons general have made powerful impacts on the nation’s health.

Dr. Murthy’s advisory drew immediate plaudits from the American College of Obstetricians and Gynecologists, an organization that is particularly concerned about false information suggesting Covid-19 vaccines might be harmful to pregnant women. There is no evidence of that.