Yeah, a flu vaccine’s effectiveness can be as high as 60%, but they do not tell you it can be as low as 2% or an average between the two. This is according to the CDCs own information. What does this mean for the Covid-19 vaccine when it comes out? Are they going to force something that only may help 50% of the time? Always do your own research. Vaccine Effectiveness: How Well Do the Flu Vaccines Work?