"The first effective coronavirus vaccine can prevent more than 90% of people from getting Covid-19, a preliminary analysis shows."
https://www.cdc.gov/flu/prevent/misconceptions.htm
and this
https://www.cdc.gov/flu/prevent/vaccine-benefits.htm
you'll see that that's not how it always works.
> Flu vaccination can reduce the risk of flu-associated hospitalization for children, working age adults, and older adults.