Because there is no vaccine for HIV, the only way people can prevent infection with the virus is to avoid behaviors putting them at risk of infection, such as sharing needles and having unprotected sex.

Many people infected with HIV have no symptoms. Therefore, there is no way of knowing with certainty whether a sexual partner is infected unless he or she has repeatedly tested negative for the virus and has not engaged in any risky behavior.

Abstaining from having sex or using male latex condoms or female polyurethane condoms may offer partial protection, during oral, anal, or vaginal sex. Only water-based lubricants should be used with male latex condoms.

Although some laboratory evidence shows that spermicides can kill HIV, researchers have not found that these products can prevent a person from getting HIV.

Recently, NIAID-supported two studies that found adult male medical circumcision reduces a man's risk of acquiring HIV infection by approximately 50 percent. The studies, conducted in Uganda and Kenya, pertain only to heterosexual transmission. As with most prevention strategies, adult male medical circumcision is not completely effective at preventing HIV transmission. Circumcision will be most effective when it is part of a more complete prevention strategy, including the ABCs (Abstinence, Be Faithful, Use Condoms) of HIV prevention.