Population density is indeed important, but averaging over whole countries gives the wrong impressions. Covid was deadlier in urban areas. Compare rural region

Population density is indeed important, but averaging over whole countries gives the wrong impressions. Covid was deadlier in urban areas. Compare rural regions, such as the ones bordering Norway and Sweden, and the mortality is pretty much comparable across the border. Slightly on the Swedish side, but well within what can be ascribed to random variability. That doesn't make the border closings look especially effective in retrospect. The virus doesn't care about borders.