Swedish climate activist Greta Thunberg says on social media that she believes she has recovered from mild symptoms of COVID-19 experienced during a period of quarantine following a European trip.

The teenager called on young people to protect groups at greater risk from the disease. Thunberg says her mild symptoms are “what makes it so much more dangerous” due to the risk of on passing the virus without knowing it.

Sweden only tests patients for coronavirus if they require hospital care. Others are urged to isolate themselves and rest. She urged people to stay at home to slow the spread of the pandemic.