I think a key difference between Denmark and Singapore is lockdowns. Denmark had lighter lockdowns and less restrictions than many places, and has recently removed them all one by one until they were gone. Singapore has been heavily locked down, and continues to get more and more restrictive. I think the lockdowns stop people from encountering Covid as often, and that slows herd immunity. In places like Sweden, the people can't get sick now, they're immune. Like myself since March 2020. We need less lockdowns and vaccines, more freedom and natural immunity : )