The fact that COVID-19 often presents in mild fashion, or is even asymptomatic in people who test positive, is the very reason this novel coronavirus may succeed in attaining endemic status in the human population.
The two previous novel coronaviruses, SARS and MERS, consistently presented with a severity that was counter-productive to the viruses' attaining endemic status, both because killing the host limits spread and because the severity of presentation aiding in tracking victims.
If the coronavirus causing COVID-19 attains endemic status, then it can mutate in the human population, as the influenza virus does, and require the constant development of shifting vaccines to keep up with the mutations, as is true of the flu.
Such is the case made in the linked article from the Atlantic. This is not a doomsday scenario but if, in fact, on a continuing basis, cold and flu season becomes "cold and flu and COVID-19 season", that's a big deal, in historic terms.
https://www.theatlantic.com/health/archive/2020/02/covid-vaccine/607000/