There were concerns because SARS vaccine attempts hadn't been further developed due to apparent cytokine storm problems. I think we're far enough along to be confident that that isn't an issue with vaccines for this virus.

Some people also make a comparison to the common cold coronaviruses which have a lot of strains and might be rapidly mutating. Honestly, it's a bad comparison because it's clear this coronavirus isn't mutating rapidly, and besides we haven't really tried to target common cold coronaviruses - why would we when rhinoviruses are the most frequent cause of the common cold?