- A source of something provides that something
- Vaccines are a source of long-term immunity against some diseases for the human body
- Hence, vaccines provide the body with long-term immunity against some diseases

Hence, vaccines provide the body with long-term immunity against some diseases
Question
Which of the following can provide the human body with long-term immunity against some diseases?

Context
- A source of something provides that something 
- Vaccines are a source of long-term immunity against some diseases for the human body