An experimental coronavirus vaccine has shown early signs of success after volunteers developed antibodies against COVID-19, a US biotech company says.

Moderna will start testing its vaccine on thousands of people in July after the company’s chief medical officer, Dr Tal Zaks, declared it “actually works” due to its ability to “stimulate the immune system”.

He announced that each one of Moderna’s 45 volunteers who received the vaccine developed antibodies that might protect them from falling sick with COVID-19.

The research has not been peer-reviewed or published in a scientific journal, but the data does provide some hope for scientists that the experimental drug could work to protect people from the virus.

These results come from phase one of Moderna’s trial, which assesses how safe and effective the vaccine is when it is injected in a handful of subjects.

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Volunteers who had the lowest dose possible elicited a similar response to that “naturally” seen in recovered coronavirus patients, the company said.

“These interim phase one data, while early, demonstrate that vaccination with mRNA-1273 elicits an immune response of the magnitude caused by natural infection,” Dr Zaks stated in the company’s official release.

“These data substantiate our belief that mRNA-1273 has the potential to prevent COVID-19 disease and advance our ability to select a dose for pivotal trials.”

Meanwhile, those who received a medium dose benefited from “more antibodies” than naturally recovered patients.

Volunteers suffered minor side effects, including redness and soreness from the jabs, but it was “generally safe and well-tolerated”, Dr Zaks said.

Based on preliminary data, Dr Zaks predicted the vaccine would likely go on the US market at “about the end of the year, the start of next year”.

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The positive early results drove the company’s shares to jump as much as 39 per cent.

While the company has passed only the first phase of its human trial, Goldman analyst Salveen Richter predicts the vaccine has a 75 per cent chance of success.

The bank is “optimistic on the forward outlook for the vaccine” and expects phase-two trials to begin in the current quarter, Business Insider reported on Tuesday morning.

Moderna must now see how 600 more volunteers respond to the jab as part of its second phase, which has already received the green light from the US Food and Drug Administration.

Then comes the third phase, which the company said would begin in July. It will be the largest and most important to validate the efficacy of the vaccine.

Moderna CEO Stephane Bancel said the preliminary tests inspired confidence that mRNA-1273 had “a high probability to provide protection” against the virus.

“We could not be happier about these interim data,” Mr Bancel said of the phase one.

-with agencies