In the context of a pandemic there's also the relative fitness (strain vs strain) optimization. So a more lethal virus during a pandemic must also be more tran

In the context of a pandemic there's also the relative fitness (strain vs strain) optimization. So a more lethal virus during a pandemic must also be more transmissible, as it's actively competing for the same susceptible hosts with other circulating strains. If another strain gets there first, chances are it's going to prime that host's immune system sufficiently to prevent reinfection. Which means it needs not just more lethal mutations, but also more transmissible ones. The probability of all of those coinciding seems low, as the former are more likely to arise in immunocompromised hosts, and the latter in circulation among dense populations, no?