Billie Eilish thinks she “would have died” from COVID-19 if she wasn’t vaccinated.

The 19-year-old singer has opened up on her battle with the respiratory illness and revealed she’s still experiencing side effects months after her health battle.

Appearing on ‘The Howard Stern Show’ on Monday, she said: “I didn’t die, and I wasn’t gonna die, but that does not take away from how miserable it was.

Billie Eilish. Picture: Instagram

“It was terrible. I still have side effects. I was sick for, like, two months almost.”

She credited the vaccine with her being “fine” now, and admitted she felt “f****** horrible” when she was battling the coronavirus.

She added: “I want it to be clear that it is because of the vaccine I’m fine. I think if I weren’t vaccinated, I would have, like, died, because it was bad…

“When I say it was bad, I more just mean that it felt horrible. But really, in the scheme of COVID, it was not bad. You know what I mean? When you’re sick, you feel f****** horrible.”

Despite that, Billie has been busy this year and has started working on her third album – the follow up to 2021’s ‘Happier Than Ever’ – with her brother and collaborator Finneas O’Connell.

Billie Eilish arrives at the Oscars in Los Angeles. Picture: AP Photo/John Locher, File

Speaking to Rolling Stone magazine, he said they were “really excited to start working on” new material, and noted while the duo have “interesting skeletons” for new tracks, they are “not sure what animals they are”.

He added: “We’ve got the net in the ocean, and we’re picking up detritus.

“And then you sift through all that, and you pick out the treasure, and then you have an album. I’m really excited. I think we’ve got a lot to say.”

However, Finneas dismissed the idea of Billie dropping her third album in 2022, noting that their focus is on her ‘Happier Than Ever’ world tour, which starts in February.

He explained: “This tour is this album. We’ve played some festivals, but we haven’t done Billie headliner solo shows, and we’re really excited to play ‘Happier Than Ever’ on the road.

Finneas. Picture: Instagram

“So even if it’s in the can by February, we’ll [delay it] for a little bit. Because I like letting projects breathe…

“You don’t want to step on the toes of an album like that. You make your stuff mean less, I think, when you do that.”