I believe the answer is: positive externality
Positive externality refers to The benefit that enjoyed by a third party when the first and second party are conducting a transaction.
When you receive a vaccines, you prevent yourself from becoming a host that could contaminate other people from getting the virus. In the example above, you and your children are the first and second party. And other children are the third party.
Whereas theDepartment of Defense is charged with military actions abroad, theDepartment of Homeland Security works in the civilian sphere to protect the United States within, at, and outside its borders. Its stated goal is to prepare for, prevent, and respond to domestic emergencies, particularly terrorism.