The climate change activist said she fell ill after returning home from a trip in central Europe.
She started feeling tired and suffered shivers, a sore throat and a cough, while her dad, actor Svante Thunberg came down with a fever.
The 17-year-old has stayed inside for the last two weeks and is now urging others to stay at home to stem the outbreak.
She said: ‘For the last two weeks I have been isolated and then I got the virus.
‘I came home from central Europe and then I isolated myself from the beginning, because I thought I might as well as I’ve been on trains and so I don’t want to put anyone else at risk.
‘But then I started feeling some symptoms after a few days. But the important thing is that I didn’t basically feel that I ill.
‘At the same time my father was feeling much more intense symptoms.’
She added: ‘I didn’t basically feel that I was ill. It could be that I was feeling unusually tired, I was coughing a bit.
‘That is because I’m not in a risk group, I didn’t get it very seriously. That also is very dangerous because you don’t know you have it.
‘If I wouldn’t have been for my father getting it at the same time and much more intense than me, I might not even have noticed it that I was sick.’
‘Many people don’t feel symptoms at all, or very mild symptoms, but it can be contagious.
‘That is something I want to communicate, that many people don’t feel symptoms at all, or very mild symptoms, but it can still be contagious. So you have to really practice social distancing whether you feel ill or not.’
She added: ‘So of course I’m not 100 per cent sure I have got it. But it would have been very strange if it would have been something else, because it just fits very… especially with my father’s reaction, it’s exactly fitting with the symptoms.’
“Now I’ve basically recovered, but – AND THIS IS THE BOTTOM LINE: I almost didn’t feel ill. My last cold was much worse than this!
“Had it not been for someone else having the virus simultaneously I might not even have suspected anything. Then I would just have thought I was feeling unusually tired with a bit of a cough.
“And this it what makes it so much more dangerous. Many (especially young people) might not notice any symptoms at all, or very mild symptoms.
“Then they don’t know they have the virus and can pass it on to people in risk groups.
“We who don’t belong to a risk group have an enormous responsibility, our actions can be the difference between life and death for many others.
“Please keep that in mind, follow the advice from experts and your local authorities and #StayAtHome to slow the spread of the virus. And remember to always take care of each other and help those in need.”
More to follow.