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For people with HIV who wish to breastfeed (chestfeed*), having an undetectable viral load greatly lowers the risk of transmission but does not completely eliminate it. For this reason, it is recommended that people with HIV formula feed rather than breastfeed their babies in Canada. However, there is a growing movement to support people with HIV who wish to breastfeed. This article will explore research about the risk of transmission through breastfeeding and factors that reduce the risk. It will also look at the reasons why a person may choose to breastfeed and ways that service providers can support people with infant feeding, whatever choice they make.

*A note on language: Chestfeeding is a gender-neutral term for breastfeeding, which is preferred by some people. We have used the term breastfeeding throughout this article, as this is the most commonly used term. When working with a client, it is important for service providers to ask them what terms they prefer and to use their preferred terms.

How HIV transmission can happen through breastfeeding

The biology of how HIV transmission happens through breastfeeding is not perfectly understood.

Transmission of HIV through breastfeeding is thought to occur when the mucosal membranes that line the back of the infant’s throat and stomach are exposed to breast milk that contains HIV.1 HIV can enter the infant’s body through these membranes in the throat or the stomach, where it can replicate and spread throughout the body to cause a permanent infection. Newborn babies are particularly vulnerable to HIV and other infections because their immune systems and their bodies are still developing.1

The viral load of the breastfeeding person is an important factor for HIV transmission during breastfeeding. Viral load is a measure of the amount of HIV in a bodily fluid, such as blood or breastmilk. An undetectable viral load in the breastfeeding parent substantially decreases the likelihood of transmission. So why doesn’t an undetectable viral load eliminate the risk for transmission through breastfeeding? It’s because HIV can live in the infected immune cells, where it is not detected by routine viral load tests. HIV can remain dormant, hiding in the immune cells, even when the viral load is undetectable.1 When HIV is hiding in the cells, it also can’t be killed by HIV treatment. If the immune cells that contain HIV are called upon to fight an infection in the breast, or in the gut of an infant, the cells can start producing large amounts of HIV in the breastmilk, which can cause HIV transmission to the infant. Other factors that can increase the risk of transmission include inflammation in the breast (caused by mastitis, breast abscess or engorgement); breastfeeding for a longer period of time; and mixed feeding (feeding a baby solid food as well as breastfeeding rather than exclusively breastfeeding).1

What we know about the risk of HIV transmission with and without an undetectable viral load

Without treatment, the risk of HIV transmission through breastfeeding is estimated to be about 15%.2,3 Research shows that HIV treatment reduces the chance of transmission through breastfeeding, but it does not eliminate the risk.

A systematic review found that among women on HIV treatment who breastfed, there was a 1% transmission rate after six months of breastfeeding, which increased to 3% after one year.4 However, the women were on treatment for varying amounts of time and were not given treatment beyond six months after giving birth, and the systematic review did not account for adherence to treatment or for viral load. This means that we do not know how many participants were taking treatment consistently or had an undetectable viral load at the time of transmission.

Only a few studies have measured the risk of transmission through breastfeeding when the mother was on treatment and had an undetectable viral load. The largest study to do so is called PROMISE and was done in several African countries and India.5 Among the 1,220 infants whose mother was taking treatment, seven acquired HIV through breastfeeding, an infection rate of 0.57%. In five out of the seven cases, the mother had a detectable viral load at their most recent viral load test before the baby tested positive. In the other two cases, the mother had an undetectable viral load at their most recent viral load test. This means that some infants acquired HIV despite the mother being on treatment and having an undetectable viral load near the time of transmission.

Three smaller studies have also looked at HIV transmission through breastfeeding in the context of treatment and an undetectable viral load.6–8 Two of those studies found no transmissions when the mother was taking treatment and had an undetectable viral load throughout the time they were breastfeeding.6,7 In the third study, two infants acquired HIV although their mothers had an undetectable viral load at their last test.8 Taken together, these studies suggest that the risk of transmission when the parent is on treatment and has an undetectable viral load is very low but not zero.

HIV medication for the infant to reduce the chance of HIV transmission

Research shows that the risk of HIV transmission through breastfeeding can also be dramatically reduced by giving the baby HIV medication for the period when they are breastfed.9,10 This is known as extended infant prophylaxis. This generally consists of medication given daily for the duration of breastfeeding and up to a few months after breastfeeding is stopped.10,11 The chance of HIV transmission varies depending on factors such as the medication(s) used for prophylaxis and the duration of time it is given to the infant.8 Some studies have found that the rate of HIV transmission when the infant was on prophylaxis was around 1%.10,12

There has not yet been a large study where the breastfeeding parents were taking treatment and their babies were taking prophylaxis at the same time. Experts have called for more research to better understand the risk of transmission when the parent is on successful HIV treatment and the infant is receiving prophylaxis.1,13 One small study in Canada documented the care of three babies whose mothers were supported to breastfeed. The mothers received treatment and had undetectable viral loads, and the infants received extended prophylaxis for the duration of breastfeeding. None of the babies contracted HIV.11 Another study in the United States reported on nine mothers living with HIV who were supported to breastfeed their 10 babies, using a similar protocol. All of those babies remained HIV-negative as well.14

Guidelines about infant feeding, and the movement to support people who choose to breastfeed

In high-income countries like Canada, it is recommended that people with HIV use formula to feed their babies rather than breastfeed, even if they have an undetectable viral load.15 This is because available evidence indicates that there is a small risk of HIV transmission to the infant through breastfeeding, even when the parent’s viral load is undetectable.

In many low-income countries, the recommendations are very different. In these settings it is recommended that people with HIV take treatment and breastfeed.16 This is because in these countries, the risk of passing HIV to a baby is outweighed by the benefits of breastfeeding for the baby’s health. Breastfeeding helps to build the baby’s immune system to fight life-threatening infections that are common in these countries, and it can help to prevent malnutrition. It is also safer than formula feeding if the person does not have access to clean water to mix with formula. The differing guidelines in different countries can be confusing for people, especially people who immigrate to Canada from a country where the recommendation and the cultural norm is to breastfeed.13

Another point of confusion is that Health Canada recommends breastfeeding over formula feeding for people who do not have HIV.17 This can make the decision to formula feed complicated for people who may have heard that “breast is best” for a baby’s health and development.13

Guidelines in Canada and other high-income countries are increasingly providing recommendations to support people who choose to breastfeed. Canadian guidelines, which were recently updated, still recommend exclusive formula feeding, but they also include recommendations on how to support someone who chooses to breastfeed. These recommendations include consultation before the baby is born, ensuring that the parent is supported to be able to maintain an undetectable viral load, and extended infant prophylaxis and monitoring for the baby. The guidelines also state that service providers should not report a person living with HIV to child protective services or police for breastfeeding.15

Reasons why people with HIV may wish to breastfeed, and challenges that they may face

In addition to the health benefits associated with breastfeeding, there are many personal, social and cultural reasons why a person may wish to breastfeed.13,18,19

Many people have a strong desire to breastfeed for a variety of reasons. Some of these reasons include feeling that breastfeeding helps with bonding to a baby, feeling that breastfeeding is the healthiest thing for a baby, and a belief that not breastfeeding may make them a bad parent.18–20

There are also social pressures to breastfeed. Breastfeeding is a social and cultural norm in many communities.19,20 In Canada and around the world, many people have a belief that “breast is best,” and people who choose to formula feed may face judgment or questioning about their choice from their family or community.9,21 In some communities, not breastfeeding may “out” someone as HIV positive, and the fear of having one’s status known may impact a person’s decision about whether or not to breastfeed.18

On the other hand, people with HIV who choose to breastfeed may face stigma from healthcare or other service providers who know their status. Fear of stigma, judgment and being reported to law enforcement or child protective services may make people hesitant to tell their healthcare providers that they are breastfeeding. Some people may then breastfeed without telling their healthcare provider for fear of these repercussions.22–24 This is problematic because if the healthcare provider doesn’t know that their patient is breastfeeding, they cannot provide the supports necessary to reduce the risk of transmission.

How service providers can support people with infant feeding

The decision on how to feed an infant can be a difficult one for people living with HIV. Service providers should be prepared to have open discussions with pregnant people living with HIV about their plans for feeding their babies. These discussions should include the following:

  • Ask clients about their feelings about infant feeding, and listen to their desires and concerns non-judgmentally. If a client shares that they have a desire to breastfeed, assure them that this is very normal and provide them with information to make an informed choice.22
  • Make clients aware that the recommendation in Canada is to exclusively formula feed, and if necessary, explain why it is different from the recommendation in some other countries.
  • Reassure clients that formula feeding is safe and healthy.

If a client decides that they will formula feed their baby, service providers can support them in the following ways:

  • Help to connect them with a free formula program if there is one available in the region.
  • Discuss concerns about formula feeding and offer strategies for managing these concerns (such as ways to bond with a baby without breastfeeding and help in deciding how to explain to friends and family why the baby is not being breastfed).

If a client decides to breastfeed, service providers can support them in the following ways:

  • Encourage them to connect with a healthcare provider to support their decision to breastfeed as safely as possible. This might include referring them to an HIV specialist who is willing to provide the necessary support including HIV medication and monitoring for their baby.
  • Provide support to help ensure they are able to take their HIV treatment and maintain an undetectable viral load. This can include providing practical tips for how to remember to take pills. It can also include helping to address broader issues in a person’s life that can make it difficult to adhere to treatment, such as insecure housing, substance use and mental health challenges.

Related resources

Canadian Paediatric and Perinatal HIV/AIDS Research Group consensus recommendations for infant feeding in the HIV context - guideline  

CATIE statement on the use of antiretroviral treatment (ART) to maintain an undetectable viral load as a highly effective strategy to prevent perinatal transmission of HIV – CATIE statement

HIV Transmission – fact sheet

Having a baby: What People Living with HIV Should Know about Pregnancy and Infant Feeding – client resource


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About the author(s)

Mallory Harrigan is CATIE's knowledge specialist, HIV testing. She has a master’s degree in community psychology from Wilfrid Laurier University.

Externally reviewed by: Dr. Sean (Ari) Bitnun & Catherine Rutto