Should flu vaccine be taken annually is necessary for us? Who always can't predict the right strain for vaccine, we still suffer from the novel virus.

Get shot annually. The flu virus changes, so it's important to get vaccinated every year. The cdc usually does a pretty good job of predicting which viruses will be circulating. Sometimes they miss, but if you don't get the shot you have no chance of being protected.
Helpful. The components of the flu vaccine are based upon predictions from strains known to be starting, usually in asia, which spread over the rest of the world. There is a certain amount of guesswork, and they are rarely exactly right, but get enough of an immunity in place to lower the risk for the population as a whole. It is best to follow the recommendations of public health officials.