Assuming that Denmark vaccinated oldest/most vulnerable first, this could be a confounded estimate (because age both means you got the vaccine first, and that your immune system will be less effective against Covid).

Personally, I think it's a statistical fluke, and was going to argue that it must be due to a smaller sample size until I saw the width of the confidence intervals (CI's get narrower as observations increase).

Very odd, and I'll be surprised if that makes it through peer review intact.