This is tricky to understand, but "all cause excess mortality" is pretty well understood by statisticians. They use it all the time for flu. Here's one documen

This is tricky to understand, but "all cause excess mortality" is pretty well understood by statisticians. They use it all the time for flu. Here's one document from the UK that mentions the kind of testing they do to arrive at "deaths to flu" figures. They have international programmes to see what respiratory diseases are circulating, they test people who arrive in hospital for those, they know roughly how many people in the population they expect to die (because RTAs, cancer, heart disease, etc all stay sort of stable from one year to the next). They also do survey work to see if people have flu symptoms but haven't seen a doctor, and they can see how many people attend various healthcare settings for flu. It's all a lot more complicated than "did someone write flu on a death certificate". https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/526405/Flu_Annual_Report_2015_2016.pdf https://assets.publishing.service.gov.uk/government/uploads/...