As Covid-19 cases have climbed as part of a late-summer uptick, right-wing influencers and conspiracy theorists have responded by stoking fears about mass lockdowns and spreading unsubstantiated new ideas about Covid-19’s links to world events.

“Do they want Covid measures back to put us on war footing in preparation for the war with Russia?” Jack Posobiec, a right-wing personality, said to more than 150,000 followers on his Telegram channel.

There is little evidence that the current wave of Covid-19 cases will prompt the kinds of extreme countermeasures seen during the worst of the pandemic. The share of Covid-19 cases nationwide peaked at 14.1 percent in August — in line with most surges since the pandemic began — but hospitalizations were at near historic lows.

Officials have instead responded with targeted efforts, noting that the country was benefiting from wider immunity, better treatments for the sick and more accessible tests that can help prevent surges from becoming full-blown crises.

But to conspiracy theorists and right-wing influencers online, each uptick is an opportunity to sow fear and rile up their supporters, according to disinformation experts. The use of “plandemic” and “scamdemic” — two terms describing Covid-19 as a ruse — rose sharply in August on right-wing websites, according to data from Pyrra, a company that monitors threats and misinformation on alternative social networks.

“I would almost call it an obsession for the Covid denier, anti-vax community,” said Welton Chang, the co-founder and chief executive of Pyrra. “They just make mountains out of molehills for every little thing.”

Misinformation about Covid-19 is as old as the virus itself. Much of it is about vaccines: One-third of Americans said they believed that the Covid-19 vaccines caused thousands of sudden deaths in otherwise healthy people, according to a survey published in August by the KFF, a nonprofit research group. While there is no link between Covid-19 vaccines and sudden deaths, conspiracy theorists have often circulated the idea as celebrities and athletes fall ill from unrelated causes.

In many right-wing spaces online, users still claim without evidence that the virus is a planned bioweapon, that vaccines contain microchips or that unproven medicines offer simple cures for the virus’s symptoms. As Covid-19 becomes recurring like the flu, disinformation experts warned that the false and misleading ideas swirling around the pandemic will continue evolving.

The latest misleading claims sprung after comments by the Biden administration in late August, when it issued warnings of a fall wave of Covid-19 infections. Health officials recommended Americans get vaccinated against new subvariants using forthcoming booster doses.

The reaction was swift.

“RED ALERT!” ran one headline this week on Infowars, the conspiratorial website run by Alex Jones, the right-wing fabulist. “White House Announces Plan to Reimplement Covid Tyranny.”

The rise in cases has also activated conservative politicians, who have found that criticizing lockdowns and mask mandates is a politically potent message for Republican voters.

“No mask mandates,” Vivek Ramaswamy, a Republican who is seeking the presidential nomination, told The Daily Signal, a right-wing news site. “No vaccine mandates. No lockdown ever again.”

Rep. Marjorie Taylor Greene, a Republican from Georgia, said this month that the rising caseloads were being exaggerated by Democrats to “distract people” from the party’s political failings.

“We’re going to have more Covid to increase mass hysteria and fear,” she said on Infowars, the conspiratorial talk show hosted by Mr. Jones.

Former President Donald J. Trump, the front-runner for the Republican nomination, has asserted his opposition to vaccines and other countermeasures that he once advocated for as president. He posted a video last week to Truth Social, his social network, claiming that concerns over Covid-19 variants were part of a ruse to reinstate vote-by-mail policies used during the 2020 election.

“The left wing lunatics are trying very hard to bring back the Covid lockdowns and mandates with all of their sudden fear-mongering about the new variants that are coming,” he said. “Gee whiz, you know what else is coming? The upcoming election.”