> That tantamount to saying "for people alive January 1st 1950, the Second World War was not a significant cause of mortality"

That’s a nonsense comparison because the thing they are studying is the vaccine, not COVID itself. The vaccine was available at minimum, what, end of 2020? Exposure being defined as first dose May-October 2021 does not seem unreasonable at all (and probably not arbitrarily chosen right - it’s probably something to do with the availability of data)