Most of the people who are super vulnerable to COVID (diabetes, heart disease, advanced age, etc) would already be dead of their preexisting conditions in the 50s, so I doubt it would be seen as such an issue.
The 50s just changes the dynamics, todays super-unhealthy and vulnerable 75 year olds are that era’s frail 60-65 year olds and a lot of chronic conditions that are now quite manageable are crippling by the time many are in their 40s-50s.
Life expectancy up to age 60-65 is primarily based on reducing infant and child mortality up to age 5 plus hygienic practices and basic care for childbirth. Then it’s medical advances that push the expectancy higher for your average person.
For a place like the US, the positive of far less obesity would likely be offset by the truly insane cigarette consumption plus all the other chronic health conditions. The other factor would be far less to no ability to cut transmission via remote or individualized work and the situation is closer to grocery workers and those in meat packing plants for a far larger segment of the population.
My bet is that original-version COVID death rates would be a somewhat higher in younger populations mostly due to factory conditions and high viral loads. The death rates would be moved back about 10 years for each age group, so:
Under 20, still minimal
20-40, maybe .1-.25% depending on the type of work with some percentage getting debilitating long COVI
40-50, maybe 1-2%, 5% with one of the risk factors (a little worse than OTL’s 50-60)
50-60, 5% with high risk factors being closer to 10-15% (closer to 70+)
60-70, 10-15%, with high risk factors being closer to 20%+
70-80, 15-30% depending on conditions
80+, a doozy of a killer
It would absolutely ravage the Baby Boomer generation’s grandparents and sear itself into young minds.
I think it’d end up being ghastlier than the Spanish flu and not just based on raw numbers but percentages too.