Herd immunity...! Basically meaning their bodies created the required responce naturally....and they showed no symptoms or got sick even after getting the virus... Fact is that COViD is a very mild virus. Failed its creators it seems clearly...

https://www.news18.com/news/world/sweden-stayed-away-from-lockdown-and-its-capital-stockholm-may-reach-herd-immunity-in-weeks-2589685.html