Comment by elsherbini | Hacker News Reader

Comment by elsherbini | Hacker News Reader

Some numbers for people interested in HIV:

Many countries in southern Africa have adult prevalence rates of >10% of HIV. In other parts of Africa most countries have a prevalence of ~1% or less. On other continents most countries have less than 1%, including the US with 0.3% adult prevalence. [1] For all the people wondering why this vaccine is being tested where it is, it's because just like we did for the covid vaccine, you split people up into placebo vs vaccine groups and then wait to see how many people get the virus from each group. If rates of HIV infection are as low as in the United States, you'd need to test the vaccine on ~100-1000x more people to see if it worked.

Non sequitur, but too interesting not to share: The estimated risk of acquiring HIV from a single sexual act is way lower than I realized until recently. Receptive vaginal sex with an infected individual is estimated to lead to infection only 8/10,000 times. Receptive anal sex is ~10-20 fold higher, 138/10,000. Sharing needles with an infected person is 63/10,000 [2]. That means you could have an ejaculates worth of HIV virions in your rectum, and be uninfected 49 times out of 50. (However, HIV infects immune cells, so it's way more likely to find an immune cell to infect if there are more in the area. That means infections or inflammation from other causes increase your risk of acquiring HIV compared to having no infection or inflammation. Similarly, way more target cells in blood, so if you have epithelial damage your risk goes up.)

[1] https://en.wikipedia.org/wiki/List_of_countries_by_HIV/AIDS_...

[2] https://www.cdc.gov/hiv/risk/estimates/riskbehaviors.html

Another caveat is that infectiousness is correlated to the current viral load of the HIV+ partner in all of these acts. Most estimates like the ones you give are averages for all viral loads at varying stages of HIV infection.

Someone about a year into the infection will be around the natural low-level during the dormant phase, with perhaps only 10,000s of viral copies per ml of blood. Someone a few weeks after infection, or in the early stages of AIDS after some years, can have millions of copies per ml. The relationship between viral load and infectiousness seems to be, approximately, a simple exponential curve. One Australian study found that your odds of infection with receptive anal sex with a newly HIV+ partner at peak viral load could be as high as 1 in 3, while in the latent phase in may be more like 1 in several hundred, or even lower.

Yeah and for men doing vaginal sex the risk is way lower of getting infection than being the receptacle.

HIV had to be rebranded away from being seen as a same-sex curse to a common ubiquitous threat in the 1990s to get society to care, but its really not something thats as big of a threat for most of us as it was suggested. A lot of it was just not accurate. Generations of heterosexual people running around scared. Probably did slow transmission down, since only “heterosexual” and bisexual men were/are spreading it to women via sex. But also viral load is suppressed and suppressible now.

I mean, for women in southern Africa, some communities have HIV prevalence of ~40% to this day. 4 in 10. Despite the lower risk associated with individual instances of vaginal sex, it absolutely is something to be worried about in those communities. And because those communities have lower access to healthcare, it often goes undiagnosed and untreated for far too long.

Yes, the reality in some countries on that continent is very different, there is no parallel to the west

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