Another factor not mentioned yet is that different types of viruses differ in mutation rate and mechanism of mutation due to biochemical differences in how their genetic material is stored and copied. Viruses with small genomes that mutate quickly, like HIV, can out-evolve vaccines more quickly. And in some viruses, like influenza, recombination allows for populations with new antigens to emerge quickly when multiple strains interact in the same organism (e.g. part of swine or bird flu could recombine with another strain and cause a novel flu strain), so we have to account for this when doing epidemiological predictions for targeting yearly vaccines.
sum_ergo_sum t1_j5uifxg wrote
Reply to What determines whether we can create a vaccine for an illness or not? by ShelfordPrefect
Another factor not mentioned yet is that different types of viruses differ in mutation rate and mechanism of mutation due to biochemical differences in how their genetic material is stored and copied. Viruses with small genomes that mutate quickly, like HIV, can out-evolve vaccines more quickly. And in some viruses, like influenza, recombination allows for populations with new antigens to emerge quickly when multiple strains interact in the same organism (e.g. part of swine or bird flu could recombine with another strain and cause a novel flu strain), so we have to account for this when doing epidemiological predictions for targeting yearly vaccines.