The results are in the same league as those announced last week by drugmakers Pfizer and BioNTech, which say their jointly-developed vaccine is 90-per-cent effective in preventing COVID-19.

"This is a pivotal moment in the development of our COVID-19 vaccine candidate," Moderna chief executive Stephane Bancel in a statement on Monday.

"Since early January, we have chased this virus with the intent to protect as many people around the world as possible."

Based on the results, Moderna said it would apply to the US Food and Drug Administration for emergency use authorisation in the coming weeks.

Similar applications will be made to other drug safety authorities worldwide.

The company expects it can have 20 million doses of the vaccine, known as mRNA-1273, ready by year's end for shipment within the US and between 500 million and 1 billion doses for global distribution in 2021.

According to the World Health Organization the news is "quite encouraging" but more data is needed, chief scientist Soumya Swaminathan said.

Trial participants need to be monitored for two more months for possible side effects, she told a press conference in Geneva.

"There are many questions still remaining" about the Moderna product and about Pfizer's rival vaccine candidate that has also shown to be very effective in trials, Swaminathan said.

More needs to be known about how long these vaccines protect against the novel coronavirus, to what extent they prevent severe cases of COVID-19 disease and what impact they have on elderly people, she said.

Like the BioNTech/Pfizer venture, Moderna's approach to stopping the pandemic - which has claimed at least 1.3 million lives since jumping into human hosts about a year ago - relies on genetic editing to create an organism that will prompt an immune system response to the virus.

Unlike the other venture, Moderna's research was supported by the White House's Operation Warp Speed program, which means the US government can claim responsibility for helping push the project along.

There has been no official White House response yet, though Anthony Fauci, the government's top infectious disease expert, heralded the discovery in an interview with CNN.

"It's just as good as it gets - 94.5 per cent is truly outstanding."

More than 30,000 people took part in the Moderna study.

The study results were based on results in a placebo group and in a second group two weeks after its members received a second dose of the vaccine.

In all, researchers discovered 95 individuals who developed COVID-19. Of those 90 were in the placebo group. Eleven of the COVID-19 cases were ranked as severe, again, all in the placebo group.

"Preliminary analysis suggests a broadly consistent safety and efficacy profile across all evaluated subgroups," read a statement.

In another good sign, the company said it should be able to keep mRNA-1273 stable for 30 days at between 2 and 8 degrees, which could be possible with distribution techniques.

Initial research from the Pfizer showed its vaccine had to be stored at -70 degrees for long-term storage, which would be a logistical challenge, especially in the developing world.

The European Commission is already negotiating with Moderna to supply up to 160 million doses.

Australian Associated Press