Since the beginning of the HIV epidemic, condoms have been a cornerstone of our HIV prevention efforts -- often promoted as the most effective way to prevent the sexual transmission of the virus. However, in the past few years the number of HIV prevention options has increased and some people are interested in, or are already using, newer strategies. As a result, frontline service providers are being asked challenging questions: Are condoms the most effective strategy available? How do they compare to other strategies? This article explores the evidence on how effectively condoms prevent HIV transmission and the implications for our HIV prevention messaging.
Condoms are physical barriers used during sex to prevent parts of the body that are vulnerable to HIV infection (such as the penis, vagina, rectum and mouth) from coming into contact with fluids that may contain HIV and other infections. We currently have two main types of condoms: the male condom (also known as the external condom) and the female condom (also known as the internal or insertive condom).
What are they made of? Most male and female condoms are made from nitrile, latex, polyisopropene or polyurethane, all of which cannot be penetrated by the viruses and bacteria that cause sexually transmitted infections (STIs), including HIV.1 Lambskin condoms, which are made from sheep intestines, can be penetrated by bacteria and viruses and should therefore never be used to prevent the transmission of HIV.
To lube or not to lube? Sexual lubricants are commonly used in combination with condoms to increase pleasure. The use of lubricant is also recommended to decrease friction that can cause breakage, particularly during anal sex. Water- and silicone-based lubricants are safe to use with all condoms, but oil-based lubricants can compromise the integrity of latex and polyisopropene condoms and increase the risk of the condom breaking.
Since condoms are impermeable to viruses, shouldn't we expect them to be 100% protective against HIV? Unfortunately, it's not that simple. As with any type of prevention strategy, condoms only work if they are used correctly and consistently. Inconsistent use can greatly decrease their ability to prevent HIV transmission.
Incorrect use of condoms can also compromise their effectiveness. For example, some people may use condoms that are too small or too large, damaged or expired; unroll condoms before putting them on; not pinch the tip when putting them on; use sharp objects to open condom packages; not use enough lubrication in combination with condoms or use oil-based lubrication with latex or polyisopropene condoms; or not hold the rim of the condom when pulling out. All of these can potentially increase the risk of HIV transmission by causing a condom to break, slip or leak.
Incorrect condom use can also take the form of putting on a condom late (after intercourse has started), removing the condom early (before ejaculation has occurred) or putting the condom on inside out and then flipping it over to use. If a condom is used incorrectly in these ways, then HIV transmission could occur even though the condom does not break, slip or leak.
How often do condoms break, slip or leak when they are used perfectly in every possible way? We don't know and probably never will. However, when condoms are used correctly, the rates of breakage, slippage, and leakage are likely quite low. Research shows that education and more experience using condoms can help lower rates of condom failure.3,4
The best evidence we have on the effectiveness of male condoms comes from an analysis of 14 observational studies that enrolled heterosexual serodiscordant couples (where one partner is HIV-positive and the other is HIV-negative).5 The analysis compared the rate of HIV transmission between couples who said they always used male condoms to the rate among couples who said they never used male condoms. The analysis found that the rate of HIV transmission was 80% lower among couples who reported always using condoms.
For many people working in HIV prevention, an 80% effectiveness rate may be lower than you thought or have previously told clients and patients. However, it is important to consider the limitations of this analysis when interpreting its results. There are three reasons why this analysis may make condoms look less effective than they can be:
Given these limitations, the estimate of 80% likely does not reflect how effective condoms can be in preventing heterosexual HIV transmission. If used consistently and correctly, condom effectiveness is likely much higher.
Are male condoms also effective at reducing HIV transmission when used by gay men or other men who have sex with men? Several studies have explored this question and estimated a similar effectiveness rate of 70 to 80% for consistent condom use during anal sex.6-8 However, these studies are affected by the same three limitations as studies of heterosexual couples -- incorrect use, inconsistent use and differences in behaviour. So the effectiveness rate for consistent and correct condom use during anal sex is likely higher.
No studies have evaluated the effectiveness of female condoms in preventing HIV transmission during vaginal sex or anal sex. However, research shows that they are as effective as male condoms at preventing other STIs.9-11