SCIENTISTS have hailed the "tremendously exciting" news that a US coronavirus vaccine may prevent 94.5% of people from getting Covid-19.
Interim data from the US firm Moderna suggests its vaccine is highly effective in preventing people getting ill and also works across all age groups, including the elderly.
Scientists said the news bodes well for other Covid-19 vaccines, with the one for Oxford University and UK pharmaceutical giant AstraZeneca due to report in the coming days or weeks.
Moderna intends to submit an application for an Emergency Use Authorisation with the US Food and Drug Administration shortly and will submit further data on the vaccine's effectiveness and safety.
The firm's final-stage clinical trial is ongoing and includes more than 30,000 people in the US.
The interim analysis included 95 participants with confirmed cases of Covid-19, of which 90 had received the placebo and five the active vaccine.
The 95 cases included 15 older adults - aged 65 and over. This included 20 people who were not white - including 12 of whom were from Hispanic or Latino/a backgrounds, four African Americans, three Asian Americans and one who was multiracial.
Severe cases of coronavirus were also examined, including 11 severe cases in the first interim analysis.
All 11 cases occurred in the placebo group and none in the group which had received the vaccine, known currently as mRNA-1273.
Moderna said its available safety data does not indicate any significant safety concerns.
The vaccine was generally safe and well tolerated, and the majority of adverse events were mild or moderate in severity, it said.
Severe events after the first dose included injection site pain and after the second dose included fatigue, myalgia (muscle pain), arthralgia (joint pain), headache, pain, and redness at the injection site.
But these effects of the injection were generally short-lived, Moderna said.
The 94.5% efficacy from this analysis could drop as further results from the clinical trial are announced.
Dr Stephen Hoge, president of Moderna, said he "grinned ear to ear" when learning about the efficacy of the vaccine.
He told BBC News: "When we got the news from the data and safety monitoring board, I'll admit I broke character and grinned ear to ear for a minute.
"Because I didn't expect, I don't think any of us really hoped that the vaccine would be 94% effective at preventing Covid-19 disease, that was really a stunning realisation."
He said combined with data suggesting it can stop severe Covid-19, it means "that the vaccine really is a terrific tool for stopping the pandemic and hopefully stopping the worst of the disease that people are facing.
"When you combine it with the news of last week of Pfizer's vaccine, you've got now two vaccines that are over 90% effective.
"It really means I think we have the tools necessary to finally beat this virus back and I think that's probably the best news of the day for all of us, is that there really are now solutions in our hands and we need to deliver them to the people who can use them."
The announcement comes one week after Pfizer/BioNTech released interim study data suggesting their vaccine is more than 90% effective.
Peter Openshaw, professor of experimental medicine at Imperial College London, said: "This news from Moderna is tremendously exciting and considerably boosts optimism that we will have a choice of good vaccines in the next few months.
"First we heard 90% efficacy from Pfizer and BioNTech, then the Russians said 92% and now Moderna says 94.5%.
"This latest press release is based on a study of 30,000 US adults, including many high-risk or elderly persons.
"This gives us confidence that the results are relevant in the people who are most at risk of Covid-19 and in most need of the vaccines.
"Moderna have also announced that the vaccine can be kept in a conventional freezer (-20C) for up to six months, and that once thawed the vaccine can be kept for up to 30 days at standard refrigerator (2 to 8C). This makes the vaccine much easier to deliver."
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said: "This announcement from Moderna is a further encouragement that vaccines will be found to not only have an acceptable efficacy, but an efficacy that is much greater than we had anticipated.
"As with previous announcements, this is encouraging for other vaccines that may be expected to also have worthwhile efficacy.
"Although they reported efficacy being over 94%, there is statistical uncertainty in this, but based on these data, the likely efficacy will be better than 85% which would be greater than most scientists would have expected.
"This is the first study to report on severe cases and while uncertainty remains, the finding of no severe cases with the vaccine and 11 cases with placebo is very strong evidence that the vaccine prevents severe as well as mild disease."
He said more data was needed on the elderly "but this is definitely encouraging progress".
Professor Trudie Lang, from the University of Oxford, said: "It is very good news indeed to see another vaccine coming through with similar efficacy results as were reported last week from Pfizer."
She added: "These early results suggest that there was a representation across different age groups and diverse communities in the protected group.
"This is really encouraging and it further demonstrates that a vaccine for Covid is a real probability and that having more than one supplier should help assure better and more equitable global availability."