Johnson & Johnson says that it and the US government will invest $US1 billion to create enough manufacturing capacity to make more than 1 billion doses of a vaccine it is testing to stop the coronavirus.

J&J said it had selected its own lead vaccine candidate and would start human testing by September, with an eye on having it ready under an emergency use authorisation in early 2021, far quicker than the typical 18-month period that it takes for vaccines to be tested, approved and then manufactured.

J&J Chief Scientific Officer Dr Paul Stoffels said the company had to start ramping up manufacturing capacity now, even before it has a signal that its experimental vaccine candidate works. The company will start making the vaccine at risk, without knowing for sure that it works.

“That is the only option for us to get it on time,” Stoffels said.

The company has a manufacturing plant in the Netherlands that can make up to 300 million doses of vaccine, Stoffels said, adding that “absolutely will not be sufficient for the world.”

He said J&J is starting to build a plant in the US now so it can be ready to manufacture vaccines by the end of the year, when data from its clinical trials will show whether the vaccine works.

Nearly half of the $US1 billion will come from the US Biomedical Advanced Research and Development Authority (BARDA), which is looking to expand on J&J’s previous collaboration with the agency.

Stoffels said the company is also scouting for manufacturing plants in other parts of Europe and Asia that are capable of making the type of vaccine the company is working on.

So far, J&J has not given any doses of its vaccine to humans. But Stoffels said the coronavirus vaccine will be based on the same technology used to make its Ebola vaccine, which has been widely used in people, and the company believes it will prove safe.