Actually, you are incorrect. Each year, the flu virus is different than the last, thus constructing new vaccines is essential. There is no possible way for your immune system to battle(/"know") a strain that has never infected it.
The difference between this virus and the flu is that:
a) R0(R naught, the rate in which a virus gets transmitted) is 2 for corona and 1.3 for seasonal flu(less than 1 would indicate a decline in new cases, thus making the virus "die" in time)
b) Incubation period for the corona is 2 weeks, whereas less than 1 week for the flu(average time is 3-4 days, in which you exhibit the symptoms and your system gets rid of the virus - otherwise you would be in isolation with ventilators and such, which doesn't alter the incubation period)
c) Mortality rate for the flu is .01 - 0.5. Estimates for corona is between 1%-4.5%(4.5% is the mortality rate atm, but the number is incorrect due to lack of testing - having more confirmed cases will smash this number near .5-1%)
Even if it's a flu, it is more contagious and has a bigger mortality rate. Even if the rate is the same, being more contagious means we will have more casualties. You can do the math yourself.
As a witchhunt, there are rumors from Wuhan residents that the true casualties are around 45k instead of the 2.5k China published. If that's the case, the current mortality rate is skyrocketted to a whopping ~10%. Even if the cases are 10m, we are talking about 1% mortality rate. And there is plenty of evidence that this rate will be higher, due to the lack of ventilators in a lot of countries.