Global health advocates on the front lines of the effort to develop needed vaccines against Covid-19 outlined an $18 billion plan to roll out shots and end the pandemic’s worst phase by the end of next year.

The goal is to secure 2 billion doses by 2021 to try to halt the contagion that has sickened about 10 million people in a matter of months and created economic turmoil around the world. The World Health Organization, Gavi, the Vaccine Alliance, and the Coalition for Epidemic Preparedness Innovations are coordinating the initiative to deploy the shots, which still must show they can work in human tests.

With most of the world still susceptible to infection, “this virus could go on and on,” WHO Chief Scientist Soumya Swaminathan said Friday in a briefing with reporters. “The best bet we have really to bring an end to the acute phase of this pandemic is to have a vaccine as soon as possible.”

The challenges and stakes are immense. If researchers can fulfill their goals and successfully deliver vaccines in the coming months, supplies are likely to be limited, making it difficult to immunize global populations and halt the virus’s spread. Health groups have also warned about the risk that some countries will use their wealth to lock up supplies first.

“There is no scenario in which we will have enough doses of a successful vaccine to immunize the world in the first 18 months,” Seth Berkley, chief executive officer of Gavi, the global nonprofit, said in the briefing. “We’re always going to be in a supply-constrained environment.”

The aim will be to deploy those doses as wisely as possible, he said. The groups plan to initially prioritize health-care workers, people over 65 years old and those with medical conditions.

The urgency is rising from a health and financial perspective, underscored by a recent surge in U.S. cases. A working vaccine will prevent the loss of an estimated $375 billion to the global economy each month, they said.

Funds are needed for research, development and manufacturing investments, delivery costs and commitments from richer countries to procure about 950 million doses. The initiative, known as Covax, aims to give governments an opportunity to hedge the risk of backing unsuccessful candidates and give other nations with limited finances access to shots that would be otherwise unaffordable.

Gavi and CEPI want to build on a $750 million agreement they signed earlier this month with AstraZeneca Plc, the University of Oxford’s partner. Astra agreed to commit 300 million doses of the vaccine it’s developing with Oxford to the world, with delivery starting by the end of the year if it’s successful.

CEPI is backing vaccine projects that include experimental shots led by Moderna Inc., Inovio Pharmaceuticals Inc. and Oxford. The objective is to successfully develop at least two or three vaccines to increase supplies that could be available in 2021, according to Richard Hatchett, its CEO.

“To secure the level of funding that will be required, it’s critical to enlarge the scope of participation,” Hatchett said. “The more countries that participate, the higher the chance of success.”

This article was provided by Bloomberg News.