Developing drugs -- whether its small molecule, biologics, vaccines, or antibiotics -- is multidisciplinary in nature. As a biologist, I've interacted with chemists, pharmacologists, cell and molecular biologists, bioinformaticists, and clinicians (just to name a few) towards driving drug discovery projects. Each person has their own specialty, but we all work together in order to develop the most effective and safe drug for our target. My advice would be to major in the field that you're most excited about. If it's chemistry, go for it!! Chemistry would certainly give you the background to understand small molecule and large molecule structures and potentially interactions with their targeted receptors. If you're interested in vaccines and antibiotics, consider taking additional courses in immunology, microbiology, and virology (no need to minor in them unless you are highly interested in understanding more) to supplement your understanding as those fields are directly related to those type of drugs. Good luck!