The flue vaccine works in less than 50% cases. To be exact on average its 43% of cases. Then add the fact that less than 50% of Americans take the flue vaccine.
Now you're down to only about 20% (.43 X .50) of Americans are protected by flue vaccine. The other 80% is not.
The stats are 39,000,000 to 56,000,000 Americans suffered from flue illness during Oct 2019 to April 2020, a huge number causing up to 62,000 deaths in the USA. We're even not talking about the rest of the world.
Will a covid-19 vaccine protect more Americans than the flue vaccine does? Does anyone know how long will a covid-19 vaccine give the protection? Remains to be seen.
Regardless, it's not realistic to rule out the need for covid-19 therapeutic drugs even if there would be a vaccine.
Even with many vaccines in the pipeline, no one can say how long they will last.