sure they do mutate quickly ....sure vaccines become dated ......but there is always some similarity to the origninal , enough such that the vaccine can mitigate the virus growth in the body .......this expalins why native americans for instance were so easily killed by western diseases ....they had had no exposure whereas Europeans while they miught get sick were less likely to die .
this is a silly argument in that the results speak for themselves .....there is stacks of statistical evidence of greatly increased mortality in the none vaccinated
of course now the siutuation has changed in that this virus is not new to us anymore .....either by vaccination or by catching it we all have some degree of immunity such that it is less likely to be fatal
but there are new flu shots each year adapting to the new strains ....as there are new COVID19 shots each year .
still waiting for that 99.7% figure you quoted to be substantiated !
