I would bet is has a great deal to with travel and population density... particularly the density of old people and the high risk. I make that guess... because I have no way to figure out if some have more vitamin D than others. Vitamin D and immune system health are very important. Someday moron politicians will get smart and tell people to go outside during the day and get exercise.
Coronavirus: how Sweden Finland became a Nordic Covid-19 success story Finns have kept the worst of the pandemic at bay despite enacting a shorter lockdown than many other countries https://www.theweek.co.uk/108699/coronavirus-how-finland-became-nordic-success-story
Sweden limits testing --- is nearly out of tests. Well - that will help keep the case count down. Swedish health agency: Limit Covid-19 tests for people without symptoms https://www.thelocal.se/20201119/sweden-puts-new-limits-on-testing-to-free-capacity
Covid teaches Sweden that it is not a nation apart Few experts now hail the Swedish ‘experiment’ after the country learnt that gentle guidance is not always preferable to hard rules https://www.thetimes.co.uk/article/covid-teaches-sweden-that-it-is-not-a-nation-apart-trjnnrb5w
Sweden is being revealed for being a complete failure. Months after the COVID crisis started they are unable to test even a tiny portion of their people now that cases are rising. This is due to their earlier attitude that testing was not needed since letting the virus run wild would lead to "natural herd immunity".... an effort that completely failed. Now that they need to test and contain -- people the country is completely unprepared to deal with the COVID pandemic. Testing falls short as Sweden battles second pandemic wave https://www.reuters.com/article/us-...en-battles-second-pandemic-wave-idUSKBN27Z285