Moderna's interim analysis was based on 95 infections among trial participants who received either a placebo or the vaccine.
Though preliminary, the early results for the two vaccines suggest researchers can develop effective Covid-19 shots, which would be a big help in taming the pandemic.
With Pfizer and Moderna now saying their vaccines showed at least 90 per cent efficacy in large-scale stage three trials, Health Minister Christine Elliott said there is a team working away at how to best distribute vaccines once they arrive. Most of these complaints were generally short-lived, Moderna said.
Both these and Pfizer's vaccine candidate, which it developed in partnership with BioNTech, are mRNA-based vaccines.
Soumya Swaminathan, the WHO's chief scientist, said the Moderna announcement was "quite encouraging", but that only additional months of testing could ensure that the vaccine was safe in the longer term for all communities.
The World Health Organization (WHO) says there are 11 COVID-19 vaccine candidates now carrying out Phase 3 trials around the world. It said on 11 November that its vaccine was 92 per cent effective based on 20 infections in its large trial. It works by delivering genetic instructions that teach human cells to make a protein resembling one found on the surface of the coronavirus.
The vaccine was designed with assistance from the National Institute of Allergy and Infectious Diseases' vaccine research center; development of the vaccine has been supported by almost $1 billion in grants from the Biomedical Advanced Research and Development Authority.
Together with Pfizer's vaccine, which is also more than 90 per cent effective, and pending more safety data and regulatory review, the United States could have two vaccines authorized for emergency use in December with as many as 60 million doses of vaccine available this year. A large number of volunteers, however, experienced more severe body aches and pains after receiving the second of the two-shot treatment.
Next year, the USA government could have access to more than 1 billion doses just from the two vaccine makers, more than the amount needed for the country's 330 million residents.
The study's design called for the independent committee to conduct the first interim analysis of efficacy when 53 people came down with symptomatic Covid-19.
The Moderna vaccine reduced the risk of Covid-19 infection by 94.5%. Technically, the authorization would be for emergency use, rather than a standard approval. Both cautions apply to Pfizer's vaccine as well.
Dr. Stephen Hoge, Moderna's president, welcomed the "really important milestone" but said having similar results from two different companies is what's most reassuring.
The Moderna vaccine is given in two doses, 28 days apart.
Countries such as China and Russian Federation have already begun vaccinations.
Plans haven't been finalized, but a National Academy of Medicine committee has recommended that the first phase of vaccination cover about 5% of the population and include front-line health workers such as those in hospitals and nursing homes, workers who provide transportation and other services to health-care facilities, and first responders. Of particular note is a secondary endpoint tracking severe COVID-19 cases.
The federal government has ordered 76 million doses of Pfizer's vaccine candidate, as well as 20 million firm orders for the Moderna candidate, with an option for 36 million more.
Moderna, part of the USA government's Operation Warp Speed program, expects to produce about 20 million doses for the United States this year, millions of which the company has already made and is ready to ship if it gets FDA authorisation.