The deadly second wave of the Spanish flu is attributed to the perverse effect on viral spread of World War I. Mildly ill soldiers stayed put in the trenches, w

The deadly second wave of the Spanish flu is attributed to the perverse effect on viral spread of World War I. Mildly ill soldiers stayed put in the trenches, while those with a more serious strain were put on trains and sent to crowded field hospitals, which preferentially selected for the more lethal form of the virus. So far I wouldn't say we have a parallel situation with Covid, although if the vaccines just suppress symptoms while allowing the virus to breed and spread, it could have some bad effects.