Inspirational cystic fibrosis activist Claire Wineland dies aged 21 after lung transplant

A YouTuber famous for her inspiring videos about living with cystic fibrosis has died after a lung transplant that was hoped would extend her life.

Claire Wineland, who gained a huge online following for documenting her battle with lung disease, passed away at the age of 21, leaving behind thousands of devastated supporters.

After battling the illness her whole life, in August she underwent a successful double lung transplant, but she suffered a stroke shortly after and never recovered.

Her foundation said she had the "most peaceful passing" and died surrounded by family.

"Our inspirational founder passed away. She was not in any pain and the medical staff said it was the most peaceful passing they had ever witnessed," wrote the Claire's Place Foundation in a Facebook post.

Claire had a huge social media following due to her popular Instagram, YouTube and Twitter pages. Credit: Claire Wineland/Instagram

Her swift rise to social media popularity came about thanks to her candid, often funny, posts about illness, mortality and life.

"Life isn't just about being happy... It's about what you're making of your life and whether you can find a deep pride in who you are and what you've given," she said during a a 2017 TEDx talk posted on YouTube.

At news of her passing, tributes poured onto social media, with one user calling Claire "an inspirational and beautiful ray of sunshine".

Even politician Bernie Sanders, who she met in 2016, paid respects to Claire on Twitter, writing "you are an inspiration and brought joy to many".

In one of her final social media posts, Claire told followers how, after her health seriously deteriorated, she'd finally taken the decision to have a lung transplant.

On the prospect of new lungs she said: "I want to be alive... and that's really scary, because when you want something it opens you up to that huge fear of failing."