The chief epidemiologist from Iceland says they have failed to reach herd immunity by vaccination so far, so that means they need a third dose:
Half of those who are vaccinated are immune so we have achieved herd immunity among them. In order to develop herd immunity here in the community, more people need to be immune to the virus and it’s not possible to do that in any way other than vaccinating with this third dose, revaccinating those who are the most vulnerable.
The chief epidemiologist from Iceland says they have failed to reach herd immunity by vaccination so far, so that means they need a third dose:
https://www.icelandreview.com/society/icelands-chief-epidemiologist-curbing-infections-remains-the-goal/