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In New Study, HIV Prevention Pill Truvada Is 100% Effective
An anonymous reader writes: A study published in the journal Clinical Infectious Diseases details the recent trial of a drug named Truvada, which researchers think might excel at preventing HIV infections (abstract). The scientists administered the drug to 657 people at high risk for contracting HIV, including users of injected drugs. At the end of the study, every single subject was still free of the virus. This is encouraging news in the fight against AIDS, though it shouldn't be taken to mean the drug is perfectly effective. Since researchers can't ethically expose people to HIV, we don't know for sure that any of the subjects were definitely saved by the drug. Other studies have also had to be stopped because it was clear subjects who were on a placebo were suffering from noticeably higher rates of infection. Leaders in the fight against AIDS say this new study closes a "critical gap" in existing research by demonstrating that Truvada can work in real-world health programs.
As someone who is gay, I have done a fair bit of research in to HIV, the way people become infected, treatments, preventative measures, etc. I am not HIV positive, so perhaps not as much research as someone who is HIV positive... but in being gay, HIV is a topic that pops up. I am not a biochemist, but I know the basics.
Truvada IS one of the drugs you can take if you become infected with HIV. If you are HIV positive, it works in combination with other drugs to prevent the virus from replicating itself. It inhibits some process the virus uses to attach to other cells in order to get the cell to manufacture new copies of the virus. This means the virus is unable to replicate itself in your blood stream.
When you become HIV positive the virus also lives in parts of your body other than your blood stream. The HIV medications can't reach these locations so they just live there and it doesn't compromise your immune system for the virus to be in those parts of your body. Your blood stream is clear of the virus so your immune system operates more normally and can fight infections. But once you stop taking the drug, the component of the drug that inhibits its replication in the blood stream is no longer there. So the virus is able to then start replicating itself in your blood stream again and symptoms return.
Truvada as a preventative works because the virus can never gain a foot hold in your blood stream to make it to the other parts of your body it can live outside of the influence of the drug. If you get exposed to HIV while on Truvada, the virus just enters your blood stream, can't replicate, and it eventually dies.
At a 9% incidence rate (p=0.09), a 95% confidence interval would be 1.96 * sqrt( p*(1-p) / n ) = 1.96 * sqrt(.09*.91/388) = 0.02847, or 2.8%.
So you would have expected 35 +/- 11 cases.
A 99% confidence interval would be 3.7%, or 35 +/- 14.5 cases. So these are very promising results. Though converting 657 people to 388 person-years may be a bit suspect. Maybe HIV isn't detectable in some people after just a half year post-infection? And I'm not sure how the fact that a person can only be infected once skews the distribution (e.g. a sample of 2 people for 100 person-years has a maximum of 2 infections, while a sample of 200 people for 100 person-years has a maximum of 200 infections.)