The U.S. decision to back an effort to open up the intellectual property underpinning Covid-19 vaccines is stirring hope that more drug manufacturers, particularly in poor countries, can start churning out shots they sorely lack.

But trade officials, health authorities and pharmaceutical executives say lengthy international negotiations required to lift patent protections and technological challenges involved in making new vaccines mean the impact of such a move may not be felt for months or years.

Instead, in the short term, additional supply could come from extra capacity drug companies are currently adding, as well as new licenses they might extend to more contract manufacturers around the world. Developing-world countries have also been pressing rich countries to release unneeded vaccines to them.

On Wednesday, the U.S. said it would support a temporary waiver of provisions protecting the intellectual property associated with Covid-19 vaccines, a move developing countries have pushed for as coronavirus infections and deaths surge in poor nations.

“On the current trajectory, if we don’t do more, if the entire world doesn’t do more, the world won’t be vaccinated until 2024,” said Secretary of State Antony Blinken on Thursday during an interview on MSNBC. “We can speed this up and get that done, I think, in a much shorter time.”