There are a variety of reasons why a vaccine sponsor might choose to contract out parts of the production process for their vaccine or drug to a production facility.
Although a biopharmaceutical company might have in-house capacity to produce a new drug product, it may need extra fill and finish equipment capacity, especially during the launch of a new product. In this case, they might choose to contract the Biologics Manufacturing Centre, as an approved production facility, to complete the fill and finish stages of their product.
Some vaccines require more than one antigen, either to manage mutations or because it's designed to protect against more than one disease. To more quickly and efficiently produce this type of vaccine, a developer might choose to produce some of the antigens in different production facilities simultaneously, then combine them all during the formulation stage. In this case, the Biologics Manufacturing Centre could be contracted to produce one or more of the antigens, but the formulation and final production stages might take place in a different facility.
Many biopharmaceutical companies have long-standing contracts with specific production facilities that regularly manufacture their vaccines and other products. To produce large amounts of a particular vaccine, or to produce it more quickly, they may choose to supplement these existing agreements by contracting the Biologics Manufacturing Centre to produce part of their vaccine.