Answer:
Defense, attack, prevention, etc.
Step-by-step explanation:
After testing, they'll have to be published and endorsed, and from what you're asking "how vaccines work", I'm guessing you want a word describing what they do. If not, the word you're looking for is endorsement because that's what the FDA does after the three stages of testing have been completed successfully.
Therefore,
1. Vaccine Development Testing and Defense because vaccines do their best to defend against pathogens with antigens.
2. Vaccine Development Testing and Attack because vaccines do their best to attack harmful pathogens attempting to formulate an infection within the immune system.
3. Vaccine Development Testing and Prevention because the role of vaccines is to prevent pathogens from entering and attacking the immune system.