The explanation to the disappearing flue
Every winter, a large part of Sweden's population falls ill with the flu. But not during the winter of 2020-21. Despite the fact that many people die every normal winter from influenza, the report says dryly about 2020-21 that "since the flu season did not take place, there was no influenza-related mortality."
Number of laboratory-verified flu cases (all types) per week, this season and previous seasons.
So why did the flu disappear so completely this single winter? The official explanation can be found in the official report where we found the above graph. "The missing epidemic is due to a combination of factors, which come from the current pandemic. Part of it is that measures to reduce the spread of covid-19 both nationally and globally have reduced the spread of influenza. Another part is that a sharp reduction in travel has meant that the flu has not been introduced to Sweden or to the rest of Europe."
That sounds logical. However, there is no scientific basis for why "measures to reduce the spread" such as quarantine, washing hands, using face mask or keeping a distance would stop one type of virus but not another. Nor that one kind of virus is spread through travel, but not another.
A perhaps more plausible explanation may be that all those who became ill or died of influenza virus in 2020-21 were classified as COVID-19.