Questions about example sentences with, and the definition and usage of "Pfizer"

A: The gamut means the whole range of something. In this case, the whole range of procedures and paperwork. I think "a small possession of flowers" should be "a small procession of followers", meaning a small group of similar products. "Hot on its heels" means very close behind
Therefore, your sentence means, "The pharmaceutical company Pfizer will now begin the whole group of testing, applications and processes needed to get the regulatory permission to begin production, and that there are several other similar vaccines very close to beginning the same regulatory gamut".