Greta Thunberg has warned of the symptomless nature of the coronavirus in young people, after revealing she likely contracted the illness almost two weeks ago.

In a post on Instagram, the climate activist urged young people to stay inside to protect those more vulnerable. “Around ten days ago, I started feeling some symptoms,” Thunberg wrote, “exactly the same time as my father – who travelled with me from Brussels. I was feeling tired, had shivers, a sore throat, and coughed. My dad experienced the same symptoms, but much more intense and with a fever.”

The 17-year-old explained that because in Sweden you can’t be tested for COVID-19 unless you’re in need of emergency medical treatment, she can’t confirm that she actually had the virus, but said it was “extremely likely” given her symptoms.

Thunberg continued: “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 have even suspected anything. I would have just thought I was feeling unusually tired with a bit of a cough.”

“This is what makes it so much more dangerous,” she added. “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.”

At the time of writing, there have been over 400,000 global cases of coronavirus, with more than 19,000 deaths. In Sweden, at least 2,200 people have been infected – though the actual figure is likely higher – and 36 have died, but the country has not yet enforced any lockdown or social distancing measures.

This week in the UK, Boris Johnson announced stricter lockdown rules, with people only allowed to leave their houses for essential items, one form of exercise per day, or to travel to work “where this is absolutely necessary”. The prime minister also announced a ban on public gatherings of more than two people. The UK currently has over 8,000 confirmed cases, and 422 people have died.