"First injection" refers to the initial dose of medicine or vaccine given to someone, usually in a series of doses, for their treatment or immunization against a certain disease. Full definition
She was given first injection of kennel cough two weeks ago, and starting 3 days ago she has been sneezing quite often... (organic-pet-digest.com)
Starts first injection today but all I was told was whole procedure would be between 1500 - 1700. (pets.costhelper.com)
Phoundry enhances Intarcia's internal efforts to build upon the differentiated clinical success of its Phase 3 investigational therapy, ITCA 650, the first injection - free GLP - 1 therapy with the potential to deliver up to a full year of treatment from a single placement. (pappas-capital.com)