Camille Stoltenberg, the agency's Director General, told state broadcaster NRK that the agency's analysis now suggested less restrictive measures would have been sufficient.
“Our assessment now….is that we could possibly have achieved the same effects and avoided some of the unfortunate impacts by not locking down, but by instead keeping open but with infection control measures,” she said.
The institute reported at the start of this month that the reproduction number had already fallen to as low as 1.1 even before the lockdown was announced on March 12.
This suggests that it would not have required heavy-handed measures such as school closures to bring it below 1 and so push the number of infected people in the country into a gradual decline.
“The scientific backing was not good enough,” Stoltenberg said of the decision to close down schools and kindergartens, a policy her agency had not recommend even at the time it was instituted in March.
She recommended that if the country is hit by a second wave of coronavirus infections after the summer, it should avoid such heavy handed measures, unless levels of infection are much higher than experienced in March and April.
“I think it will take a lot. And there is a strong willingness on the part of all parties to find instruments that are more gentle and more flexible,” she said. “What is needed is a commitment from the entire population to follow the infection prevention advice.”
The agency warned in a new report on Wednesday that there was a still a risk of a second wave of infection in the autumn.
“If we manage to lift the most restrictive measures without the spread of infection growing over the summer, behavioural changes and weather changes from the autumn onwards could still cause the balance to shift so that the infection again increases,” it said.
Stotenberg is the sister of Jens Stoltenberg, Secretary General of the Nato defence alliance, and Norway's former prime minister.