“The issue of herd immunity is difficult,” Anders Tegnell said at a briefing in Stockholm on Tuesday. “We see no signs of immunity in the population that are slowing down the infection right now.”

Swedes have been more exposed to the virus than their neighbors elsewhere in the Nordic region, and every third Stockholmer tested has antibodies, according to figures published this week. That’s after the country famously opted against a lockdown, relying instead on voluntary measures.

Tegnell has in the past said that herd immunity is hard to measure and even questioned official figures. Swedish authorities have made clear that immunity isn’t a policy goal, but the nation’s exposure to the virus makes it an obvious test case for observing the theory.