The vital issue is the range of strains that the vaccine can induce immunity against them. For instance the vaccine can work in the state of manufacturers while can not work in other regions because of highly mutation rate. Also even the strain that could be defeated by the vaccine can mutate and become vaccine-resistant. This is the problem that we are confronting with other viruses with similar behavior such as Influenza, HCV and HIV.
Globally circulating strain heterogeneity in SARS-CoV-2 virus could be one of most challenges for vaccine development.
# Effectiveness of the vaccine against mutant strains.
# Side effects depending upon age, sex, predisposition to other disease.
# Cross reactivity with other drugs, therapy.
Aside from the excellent responses above--presuming we have a safe and efficacious vaccine finally, ACCESS will be the issue. One hopes we will have a couple but ramping enough manufacturing to get the vaccine to close to every one on the planet will be a huge challenge.
The next will be vaccine hoarding by wealthy nations, leaving everyone else to suffer and die, as usual.
The third in my list then is the perversions of intellectual property that will make the price absurd to satisfy bloated executive salaries and parasitic stockholders. Such efforts by Astra Zeneca, GSK, Pfizer and other nefarious players will vastly limit access as they extract more ill-gotten wealth. Literally, ill-gotten...
