This important article by James Wilton first appeared in Prevention in Focus on the CATE website here.
Une version française est disponible ici.
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.
Using condoms correctly and consistently
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.
A recent literature review of 50 studies revealed that the incorrect use of male condoms is surprisingly common.2 For example:
- Studies found that 17 to 51% of participants reported not putting on a condom until after intercourse had started.
- Some studies also reported high rates of condom problems, such as breakage (0 to 33%), slippage (0 to 78%) and leakage (0 to 7%), which could lead to HIV transmission. Errors in condom use may be partly responsible for these problems. For example, 24 to 46% of participants reported not pinching the tip of the condom and 16 to 26% reported using a condom that was not lubricated.
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
So how effective are male condoms?
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:
Incorrect use. The couples who said they always used condoms may not have been using condoms correctly. This would have increased their risk of HIV transmission and reduced condom effectiveness.
Inconsistent use. The couples who said they always used condoms, in reality, may not always use them! Some of the couples may have had trouble remembering how often they used condoms or felt uncomfortable saying that they did not use condoms. This would have increased their risk of HIV transmission and made condoms appear less effective.
Differences in behaviour. The risk-taking behaviours of the couples who said that they always used condoms may have been different from those couples who said they never use condoms. For example, couples who reported always using condoms may have engaged in behaviours that increased their risk of HIV transmission, such as having sex more often or engaging in higher-risk types of sex. If this was the case, these behaviours would have increased their risk of HIV transmission, making condoms appear to be less effective. It’s also possible that people who reported never using condoms may have engaged in behaviours that put them at lower risk of HIV transmission, such as having sex less often or only engaging in lower-risk types of sex (such as oral sex). If this was the case, this would make it appear as though there was less of a difference in HIV transmission rate between the two groups and make condoms appear less effective.
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.
Is the same true for men who have sex with men?
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.6,7,8 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.
What about female condoms?
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.9,10,11
The expanding HIV prevention toolkit
In the past decade the number of HIV prevention options available to reduce the risk of HIV transmission has increased. Some of these strategies are generating a lot of excitement because they may provide an option for people who don’t want to, or are unable to, use condoms. These include the following:
Antiretroviral treatment – which reduced the risk of HIV transmission by 96% among heterosexual serodiscordant couples in a randomized controlled trial (RCT).12
Pre-exposure prophylaxis (PrEP) – which reduced the risk of HIV transmission by 40 to 70% for gay men13 and heterosexual men and women14,15 in RCTs. Further analysis suggested that PrEP may have reduced HIV risk by up to 90% among those who always took their pills.13,14
Post-exposure prophylaxis (PEP) – which reduced the risk of HIV transmission by up to 80% in an observational study of healthcare workers exposed to HIV in the workplace.16
Observational studies suggest that behavioural strategies such as serosorting, strategic positioning and withdrawal may slightly reduce the risk of HIV transmission.17
People who want to use, or are already using, these strategies may want to know how effective they are compared to condoms. These questions can be challenging to answer and it’s important that, in our responses, we don’t compare apples and oranges. For example, comparing results from different types of studies can be problematic. Some of the new prevention strategies were evaluated using an RCT while condoms were evaluated using observational studies. Comparing the results from these two kinds of studies can be problematic for a number of reasons:
- In RCTs the two groups are randomized to ensure that there are no differences between the groups other than whether or not they received the intervention. This is important because we know that each group should have similar risk behaviours and that neither group should be more or less likely to get HIV. However, in observational studies (such as those used to assess condoms), one group could be having sex more often or engaging in riskier sex. This could impact the results and make a strategy, such as condoms, appear to be less effective than they actually are.
- RCTs create “ideal” conditions that can make a strategy appear more effective than it would be in the “real world.” For example, RCT participants are supported to ensure they use the strategy correctly and all participants are provided with a comprehensive package of prevention services, including STI testing and treatment, free condoms, and intensive adherence and risk-reduction counselling. By contrast, observational studies, such as those used to evaluate condoms, generally do not provide participants with additional supports. Therefore, these results may not be directly comparable to the results of RCTs.
When it comes to comparing the effectiveness of two prevention strategies, we need to pay attention to the research design used to measure that effectiveness. Most new prevention strategies, such as PrEP or treatment as prevention, have been evaluated using RCTs, which can tell us about the effectiveness of the strategy under “ideal conditions.” Unfortunately, we don’t know how effective condoms would be under the ideal conditions of an RCT; however, we have good reason to believe that they would be more than 80% effective when used consistently and correctly.
Implications for HIV prevention messaging
Safer sex messaging and prevention counselling need to emphasize that the correct and consistent use of condoms is a very highly effective method of preventing the sexual transmission of HIV.
When answering questions about the effectiveness of condoms, it’s important to emphasize that they have several advantages over other options. Key messages include the following:
- If a condom is used correctly and it doesn’t break, slip or leak, then it is virtually 100% protective. However, there is a still a possibility that condoms will break, slip, or leak even when used correctly. Condoms do not eliminate the risk of HIV transmission.
- Condom effectiveness does not rely on accurate knowledge of a person’s HIV status, as opposed to serosorting, which requires accurate knowledge of the HIV status of both partners—something that is often difficult to know for certain.
- Whereas the goal of some other strategies—such as PEP, PrEP or having an undetectable viral load— is to reduce the risk of an exposure leading to an infection, condoms prevent an exposure to HIV from occurring in the first place.
- Other prevention options may be less effective if either partner has an STI, a higher viral load or other biological factors that affect HIV risk whereas condom effectiveness is not affected by these.
- If they don’t break, slip or leak, condoms can reduce the risk of HIV transmission for both anal and vaginal sex to the same level. However, the risk of HIV transmission while using PrEP or when the viral load is undetectable may be higher for anal sex than for vaginal sex. (This is because anal sex has a higher baseline risk of HIV transmission than vaginal sex.18)
- Condoms also reduce the risk of other STIs, such as gonorrhea, chlamydia, herpes and syphilis.19 Although other strategies may reduce the risk of HIV transmission, they do not reduce the risk of STI transmission. This is important because STIs can increase a person’s risk of HIV transmission.20
- Condoms can reduce the risk of unintended pregnancy.
- Condoms are less expensive, more readily available and less toxic than strategies that involve antiretroviral medications, such as PEP and PrEP.
Despite the advantages of condoms, we can’t ignore the important role that other prevention strategies may play in helping someone reduce their risk of HIV transmission. Condoms are not without their disadvantages and these can make it difficult for people to use them consistently and correctly. For example, condom use can be difficult to negotiate, condoms can decrease sexual pleasure and intimacy, they need to be available at the time of intercourse, they may be difficult to use when under the influence of alcohol or drugs, and they do not allow a woman to conceive. For these reasons, some people may choose to reduce their risk of HIV transmission in other ways.
HIV prevention efforts need to focus on helping people adopt prevention strategies that are appropriate to their circumstances and will be most effective for them. If people are having difficulty using condoms or are having problems with condom breakage, slippage or leakage, counselling may help them use condoms more consistently and correctly.
At the same time, alternative strategies for reducing the risk of HIV transmission may need to be discussed with these clients. When exploring other prevention options, it’s important to clearly explain their limitations, factors that may decrease their effectiveness and how a person can keep their risk of HIV transmission as low as possible while using these strategies. No strategy—including condoms—is 100% effective; all have their limitations and can fail in different ways. Since condoms provide less than 100% protection, using other strategies in combination with condoms will help decrease a person's overall risk of HIV transmission. However, if a client or patient decreases their condom use in favour of a less protective strategy, they may be increasing their overall risk of HIV transmission.
AIDSMAP – Do condoms work?
CATIE News – High prevalence of condom use errors and problems – implications for HIV prevention messaging
Canadian HIV/AIDS Legal Network – HIV non-disclosure and the criminal law: Implications of recent Supreme Court of Canada decisions for people living with HIV: Questions & Answers
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About the author:
James Wilton is the Coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James is currently completing his master’s degree of Public Health in Epidemiology at the University of Toronto and has completed an undergraduate degree in Microbiology and Immunology at the University of British Columbia.