Vitamins will be scarce, especially with sunlight minimal. Vitamin D, etc. Vitamins can be genned chemically, I'm sure. How many of us know how, though, we think it so easy to just buy them. ... Mushrooms and gravy from larva. But not too good on Vitamin D, A, C, etc. Bugs and Mushrooms offer protein and carbohydrates, just no vitamins. But THAT can be fixed in the chem lab, easy, I think.
Scurvy is going to be a problem anyway, due to lack of vitamin C. Perhaps people need to store a 10 year supply of that. Perhaps a solution is to find atypical vitamin producers among those things that will thrive in the Aftertime climate. Can be surprising discoveries. Time for some research. Eskimos! A good research topic, for sure.