A vaccine is the best way to protect the public from HIV.
A drug that makes a person less likely to get the virus.
Drug use, however, is a major problem in the United States and around the world.
Many people still believe that drugs are safer than alcohol and tobacco, and many people also believe that using a drug is safer than not using it.
We spoke with Dr. Joseph W. Parnes, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, about how drugs and vaccines can work together.