[tupshin]

The summary text explicitly called out why that would be unethical in this case.

[asveikau]

They don't ask people to live their lives any differently than they would, nor do they expose anyone to HIV on purpose; they just track them assuming that x% of people get HIV in any given year. So they compare what X is for people who got the shot, vs those who did not.

As I skim TFA, they say nobody who got the shot ended up getting HIV, which would be statistical anomaly for the population they tested.

[smeej]

It's not "no shot," though. It's other existing, widely available forms of pre-exposure prophylaxis.

They're not comparing the new treatment to nothing. They're comparing it to existing treatments.