A Vaccine To Prevent AIDS?的用法和样例：
- An experimental drug had no effect in general in the first major test of a vaccine to prevent AIDS.
- Is there a vaccine to prevent this new infection?
- For more than 20 years, scientists have been trying to develop a vaccine to prevent H.I.
- For more than 20 years, scientists have been trying to develop a vaccine to prevent H.I.V. infection.