For years, Gilead Sciences has said its antiviral drug Truvada, used to treat and prevent HIV infection, wouldn’t face generic competition until 2021. But Gilead recently—and quietly—moved its generic expectations up a year.

That not only puts Truvada's $2.6 billion in U.S. sales on the line earlier than expected, but gives Gilead less time to convert patients over to its newer drug Descovy, which recently put up positive data as a preventative, or PrEP.

Teva is now set to launch its copycat in the U.S. next September 30, Gilead said in its most recent quarterly securities filing. As recently as February, Gilead had been saying Truvada copies wouldn't hit until 2021, citing a 2014 patent deal with Teva. The latest filing cites the same Teva deal and a 2020 rollout date.

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The generic news comes on the heels of Descovy's new PrEP data, which Gilead plans to use to expand the drug's list of indications. When the data posted in March, SVB Leerink analyst Geoffrey Porges said it “sets the stage for Gilead to actively transition the more than $2 billion in current PrEP revenue for Truvada to Descovy."

And what's more, Porges said, investors would likely expect most of that revenue haul to head Descovy’s way before Truvada’s September 2021 exclusivity loss.

While patient advocates are happy, they’re also asking questions, given Gilead's previous disclosures. The contract may have had an acceleration clause allowing Teva to move its launch date up but Gilead wouldn't comment on the contract itself.