One of the most common problems folks have when trying to find information is only using one term, or only one term for each idea. For example, take a look at the search history screenshotted below. If you are interested in vaccination, you are probably going to want to use it as one of your terms. However, if you limit yourself to only that term, you will be missing out on research that discusses inoculation. Sure, there will be some overlap between the two, which is understandable since they are synonyms, but you will be missing a lot of potentially good information by not expanding your search and including similar terms.
Do your best to identify different keywords for all your topic concepts. If you have trouble coming up with additional terms, don't hesitate to ask me!
This series of short videos will show you a few useful techniques you can use to improve your literature searches.
These two videos will give you an introduction to searching for literature in PubMed, one of the primary databases for health sciences research.