HIV transmission via breastfeeding, despite undetectable viral load
A major topic of scientific debate over the last year has been whether “undetectable = untransmittable” applies to breastfeeding as well as to sexual transmission. While we have good evidence that people who take their HIV treatment consistently and have had an undetectable viral load for several months do not pass HIV on to their sexual partners, it has been less clear whether this is also true for mothers living with HIV who breastfeed their babies.
One year ago, a leading UK paediatrician said that while effective HIV treatment greatly reduces the risk of onward transmission during breastfeeding, it does not appear that the risk is zero. This summer, Swiss doctors argued that pregnant women with HIV should be told about this uncertainty in the evidence, so that they can weigh up the potential benefits and harms of breastfeeding themselves.
Also in the summer, an international group of researchers outlined a series of research questions on the topic that remain to be answered. One of them was: Is there a level of HIV in blood plasma or breast milk below which the virus cannot be transmitted?
It now appears that the answer to that question is ‘no’. Researchers have looked back at records from a large international study conducted several years ago. They have identified two babies who tested positive for HIV DNA despite their mothers having an undetectable viral load.
In one case, there is good evidence that the mother had been undetectable for several months. In the other, the mother had only recently become undetectable, so it is possible that she was actually detectable when transmission occurred.
One possible explanation is that even when HIV is undetectable in blood, it may still be transmitted because of the persistence of what is known as cell-associated virus in breast milk. Another is that because babies consume a large volume of breast milk, the transmission risk may be higher than during sexual transmission.
This shows that we cannot say that undetectable means untransmittable in the case of breastfeeding. Recent guidance from the British HIV Association advises that, in the UK and similar settings, the safest way to feed infants born to mothers with HIV is with formula milk.
HIV-2 more dangerous than previously thought
Most people in the world who are living with HIV have HIV-1, a virus that has many different subtypes (for example, subtypes B and C).
There is also a distinct virus called HIV-2. It is most common in western Africa and is becoming more common in India, although numbers there are still relatively small. Small numbers of cases have also been seen in Portugal, France, other European countries and the Americas.
HIV-2 has long been considered to be less harmful than HIV-1, with a lower risk of AIDS and death. However, it turns out that this belief has been based on very little evidence.
Researchers compared data on a group of people in the West African country of Guinea-Bissau, from 1990 to 2013. During the study period, 225 acquired HIV-1 and 87 acquired HIV-2. The researchers had an approximate date of infection for each person and collected data on their health for up to 20 years each.
As very few people had access to HIV treatment in the country at this time, the data shows us what happens to people’s health over several years when treatment is not provided. Often, people with HIV-2 were not encouraged to take treatment because it was not thought to be needed.
The study does show that HIV-1 is a more dangerous virus than HIV-2:
- AIDS developed in 54% of people with HIV-1 and 43% of people with HIV-2.
- After eight years, half of those with HIV-1 had died. In comparison, after 15 years, half of those with HIV-2 had died.
But clearly HIV-2 is also very harmful when it is left untreated. While the rate of disease progression is slower, HIV-1 and HIV-2 follow a comparable disease course – people with both viruses progress to AIDS and death if they do not receive HIV treatment.
The main conclusion from the study is that people with HIV-2 should take HIV treatment as soon as they can, just as people with HIV-1 do. Prompt HIV treatment is recommended for all people living with HIV.
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