Tina Rosenberg. Ms. Rosenberg is a co-founder of the Solutions Journalism Network, which supports rigorous reporting about responses to social problems.

Second of two articles. Read the first one here.

Last week, the High Court of England and Wales announced a momentous decision: It invalidated the pharmaceutical company Gilead’s patent on Truvada, opening the way to generic competition.

Truvada, a combination of two drugs, is one of the world’s most-used H.I.V. medicines. For treating H.I.V., it’s used along with a third drug. But many H.I.V.-negative people also take Truvada daily as a preventive. That’s called pre-exposure prophylaxis, or PrEP.

In the United States, Truvada is available only as a brand-name drug. It costs $20,000 a year.

Here’s how it will work in Britain’s National Health Service, according to Dr. Andrew Hill, a senior research fellow at Liverpool University who studies the cost of medicines. “The N.H.S. will say to a group of generic companies: ‘We need PrEP for 20,000 people. Give us your best price.’” The cost of making PrEP is $55 per year, Dr. Hill said. He believes that the generic will sell for between $100 and $200.

All over the world, more and more people are taking H.I.V. drugs. These medicines are very good at their job — keeping people healthy and noncontagious — so most patients will take them until they die of something that isn’t H.I.V. Patients are also starting earlier on antiretroviral therapy; the new recommendation is to start immediately upon diagnosis. And now with PrEP, a potentially enormous new group of patients has arisen: H.I.V.-negative people who are at risk for catching the virus.

The National Health Service has to treat this soaring population for the same amount or less money each year. England’s region of the health service spends about half a billion dollars per year on H.I.V. drugs. There are no increases for inflation, and lots of pressures for further cuts.

It’s lucky, then, that Truvada will have generic competition. It should allow the health service to greatly lower costs and offer PrEP to anyone who needs it.

The health service does an admirable job with H.I.V. Around the world, countries measure the percentage of people living with H.I.V. who have no virus detectable in their blood. In the United States, only 49 percent have achieved this. In Britain, the number is 78 percent. Read more via New York Times