Moderna Inc's vaccine is 94.5 per cent effective in preventing COVID-19 based on interim data, the company said, becoming the second US drugmaker to report results that far exceed expectations.
Together with Pfizer Inc's vaccine, which is also more than 90 per cent effective, and pending more safety data and regulatory review, the US could have two vaccines authorised for emergency use in December with as many as 60 million doses of vaccine available this year.
The vaccines, both developed with new technology known as messenger RNA (mRNA), represent powerful tools to fight a pandemic that has infected 54 million people worldwide and killed 1.3 million.
Unlike Pfizer's vaccine, Moderna's shot can be stored at normal fridge temperatures, which should make it easier to distribute, a critical factor as COVID-19 cases are soaring, hitting new records in the US and pushing some European countries back into lockdowns.
"We are going to have a vaccine that can stop COVID-19," Moderna President Stephen Hoge said in a telephone interview.
Moderna expects the vaccine to be stable at normal fridge temperatures of 2 to 8 degrees Celsius (36 to 48°F) for 30 days and it can be stored for up to 6 months at -20C.
Moderna's interim analysis was based on 95 infections among trial participants who received the vaccine or a placebo. Only five infections occurred in volunteers who received the vaccine mRNA-1273, which is administered in two shots 28 days apart.
"The vaccine is really the light at the end of the tunnel," Dr. Anthony Fauci, the top US infectious diseases expert said. He urged Americans not to let their guard down and to continue washing hands and being vigilant about social distancing.
Even with fast authorisation, the vaccines will not come in time for most people celebrating the US Thanksgiving and end-of-year holidays, when families and friends come together - just the type of gatherings public health officials warn against.
Moderna expects to have enough safety data required for US authorisation in the next week or so and expects to file for emergency use authorisation (EUA) in the coming weeks.
The company's shares, which have more than quadrupled this year, jumped 8 per cent, while European and US stocks rose. The benchmark S&P 500 rose 1 per cent, while the pan-European STOXX 600 climbed 1.3 per cent.
Shares in Pfizer and its partner BioNTech, whose vaccine must be transported at far colder temperatures, fell 4.3 per cent and 16.4 per cent respectively, while Britain's AstraZeneca , which has yet to release any results from its late-stage vaccine trials, was down 1 per cent.
Moderna's data provides further validation of the promising but previously unproven mRNA platform, which turns the human body into a vaccine factory by coaxing cells to make virus proteins that the immune system sees as a threat and attacks.