[Fomite]

A few reasons:

- Women and girls make up the majority of HIV cases, especially in the developing world

- If you're estimating the effect in both men and women, you're reducing your power to detect an effect in either group. If you have a limited budget, it's going to be hard to recruit, etc., you may well be better off powering your study for the group you think is going to be the most impactful, then going back. We saw this with the HPV vaccine - getting it going in the highest impact groups, and then going back later

- Preventing HIV in women also prevents maternal to child transmission

- "Men with HIV" are actually two different groups - men who have sex exclusively with women, and men who have sex with men. You then also need to power your study for both sub-groups.

[mike_hearn]

That's inaccurate. The vast majority of all cases are in men. For instance in America only 22% of HIV+ people are women. Our World In Data has a map that shows this visually:

https://ourworldindata.org/hiv-aids

The only place this isn't true is sub-Saharan Africa. As there's no biological explanation for that discrepancy it's been hypothesized that it's because in Africa a lot of reported HIV cases are fraudulent, due to the large amount of AIDS/women specific foreign aid money and weak auditing standards.

[foldr]

It's not inaccurate. More than half of the people currently living with HIV worldwide are women:

https://www.unaids.org/en/resources/infographics/girls-and-w....

https://www.hiv.gov/hiv-basics/overview/data-and-trends/glob...

[mike_hearn]

The phrasing "majority of all cases, especially in the developing world" implies that it's true everywhere. Even putting that aside, it's only the bizarre situation in Africa makes the statement technically true. If we interpret it in the way it was meant to be interpreted then the statement isn't really true because everywhere that has reliable data shows the opposite: men get it the most.

[foldr]

I don't think the 'especially' has that implication when you consider the context of the article that we're commenting on. It's true that women and girls make up the majority of people living with HIV worldwide, and this is especially true of the developing world. On the other hand, your statement that "the vast majority of all cases are in men" is simply false. Depending on the interpretation of 'vast', it's arguably not even true in much of the West. For example, in the UK, about a third of people living with HIV are women; in the US it's about a quarter.

There's nothing 'bizarre' about the situation in Africa. People's sexual behaviour is different in different societies, and this can obviously influence how STIs are distributed among different groups in the population.

[bobthepanda]

There is a societal reason; condom use and polygamy. Condom use is less common and polygamy more amongst straight people in sub saharan Africa.

There was also very prominent AIDS denialism up to the 2000s so there was a bunch of lost time leading to an explosion in infections; the most notable example being South African president Thabo Mbeki.