Back when I was heavy and diabetic every winter I was sick with a cold or flu at least two weeks out of the year and sometimes a couple of times a winter. Since diet change and off insulin shots and loss of weight I mostly just don't get sick much anymore and when I do catch something instead of a week or more being sick usually only lasts two or three days. 

When I was diabetic type II I got a flu shot every year as recomended. Still got sick. Got rid of my diabetes type II with diet change, have not got a flu shot since and rarely get sick. See no reason to get it again.