-Iceland has high vaccination rates, including many people who already got both doses of Moderna vaccines several months ago
-It is too early for standard booster shots with Moderna based on medical guidelines
-Many people were originally vaccinated with other brands (J&J/Jannsen, Pfizer) which have been shown to be less effective than Moderna long-term
-Therefore, many people are "cross-vaccinating" by trying to supplement their existing vaccination with Moderna, which they view as superior
-Because of this, most/all Moderna vaccination shots performed in the last 2 months are from people with other vaccines originally -- in other words, they are only being given in ways that are not within current medical guidelines, and in a manner that has not been sufficiently studied for safety and efficacy.
If this is close enough to represent the situation, then I can see why they might decide the best move overall for public health is to halt use of Moderna, at least for now. Maybe with tighter controls, or over the coming months when there will be higher demand for prescribed Moderna boosters, then it will make sense to bring it back.