Even if they get the strains right in a flue shot, it's not 100% effective in all people.... 75% was a number I heard to be considered a good flue vaccine.Good choice if you have a president that has the power to persuade the medics and a vaccination program starts because he says it safe.
But if independent medics say it is safe (from by-effects) I would vaccinate asap.
btw. A vaccin can never guarantee it will work as it should if a virus mutates. The flew vaccin is a cocktail of vaccins and changes every year because the flew mutates. So will this Covid-19 virus.