Why can't one vaccine work for all diseases or illness?

Accurate and explained answer.

Research question: why are the carrots that grew on the left side of the garden larger than the carrots that grew on the right side of the garden? which hypothesis is based on this research question? a comparison of people with gardens to people without gardens will show who is likely to live longer. b. carrots are thought to be good for your eyesight and should be eaten regularly. c. carrots that are provided lots of sunlight grow to a larger size than carrots grown in the shade. d. eating fresh vegetables every day is a healthy thing to do.