The Law requires much, but offers no help in the carrying out of its requirements. The Lord Jesus requires just as much, yea even more (Matt. 5:21-48), but what he requires from us he himself carries out in us. The law makes demands and leaves us helpless to fulfill them; Christ makes demands, but he himself fulfills in us the very demands he makes.
It is a good idea for everyone who does not have contra-indications to receive a flu shot.