Kamala Harris has conceded that the Biden administration was blind to the emergence of the Delta and Omicron variants of Covid-19, and said she fears “misinformation” over vaccines will prolong the pandemic well into a third year.

The candid admission came in a wide-ranging interview with the Los Angeles Times, which followed reports that the vice-president was “struggling” to make a mark as Joe Biden’s No 2 and was keen for a more prominent role.

Biden’s handling of the pandemic, alongside other woes such as spiking inflation and the supply chain crisis, has contributed to a steady decline in his popularity ratings.

On Saturday, a White House official told NBC News the president would make a speech about Covid-19 on Tuesday, at which he would unveil new measures to combat the virus, including steps to “help communities in need of assistance”.

Biden would also be “issuing a stark warning of what the winter will look like for Americans that choose to remain unvaccinated”, the official said.

Harris, who has suffered the same sinking approval ratings as the 79-year-old president, was seen as shoo-in for the 2024 Democratic nomination until Biden said last month he would seek a second term. The White House said on Thursday Harris would be his running mate again.

As well as speaking to the LA Times, Harris had a heated exchange on Friday with the radio host Charlamagne tha God.

At the conclusion of a testy interview that Harris aides reportedly tried to cut short, Charlamagne tha God questioned if Biden or Joe Manchin, the centrist Democrat from West Virginia who wields outsized power in the 50-50 Senate, was the “real” president.

“C’mon, Charlamagne,” Harris snapped. “It’s Joe Biden.

“No, no, no, no. It’s Joe Biden, and don’t start talking like a Republican, about asking whether or not he’s president.”

Harris’s comments about Covid, in which she also appeared to place blame on the medical community for a lack of foresight, would seem to confirm the administration’s view that the pandemic is its biggest obstacle to progress.

“We didn’t see Delta coming. I think most scientists did not – upon whose advice and direction we have relied – didn’t see Delta coming,” Harris said.

“We didn’t see Omicron coming. And that’s the nature of what this awful virus has been, which as it turns out, has mutations and variants.”

Harris also said the public needed to be more trusting of Covid-19 vaccines, citing a slow take-up rate despite the White House and federal health officials’ efforts to urge vaccinations and boosters.

“I would take that more seriously,” Harris said of disinformation promoted in Republican circles and swirling elsewhere, successfully dissuading people from getting a shot.

“The biggest threat still to the American people is the threat to the unvaccinated. And most people who believe in the efficacy of the vaccine and the seriousness of the virus have been vaccinated. That troubles me deeply.”

Harris’s claims are backed by data analysis showing that 91% of Democrats have received a first shot compared to only 60% of Republicans. Deaths from Covid-19 are occurring increasingly in areas that voted for Donald Trump in 2020, compared to areas that voted for Biden.

The administration was handed a victory on Friday, as an appeals court said its vaccine mandate for large companies could go into effect. That contest is not over, however, as Republicans seek to take the matter all the way to the supreme court.

“We have not been victorious over [Covid-19],” Harris told the LA Times, appearing to counter Biden’s claim in July that the virus “no longer controls our lives”.

“I don’t think that in any regard anyone can claim victory when, you know, there are 800,000 people who are dead because of this virus.”

Other subjects covered in the LA Times interview included Biden’s Build Back Better domestic spending plan, immigration and voting rights, all hot-button topics on which the administration has failed to make much headway.

Harris said the failure to pass the $1.75tn economic and climate spending package, which Biden conceded on Friday would miss its Christmas deadline, was a frustration – but offered no alternative plan.

Although she blamed Republican stonewalling, the measure is being held up in particular by Manchin.

“We have to keep appealing to the American people that they should expect Congress and their elected representatives to act on the issue,” Harris said. “We can’t give up on it, that’s for sure.”