It didn't work for them and still isn't!
Sweden’s strategy of dealing with COVID-19 without implementing a lockdown has not led to herd immunity, the country’s lead epidemiologist said Tuesday. “We see no signs of immunity in the population that are slowing down the infection right now,” said Anders Tegnell, the state epidemiologist for Sweden’s public health agency.
Epidemiologist Who Refused Lockdown: Herd Immunity Isn’t Slowing COVID-19 in Sweden (thedailybeast.com)