A potential coronavirus vaccine has been deemed to be 94.5% effective at preventing people from getting the virus.
US biotechnology company Moderna made the claim - based on preliminary data - on Monday.
It comes just a week after a similar announcement from competitor Pfizer, which determined that its vaccine candidate is 90% effective.
"This is a pivotal moment in the development of our COVID-19 vaccine candidate. Since early January, we have chased this virus with the intent to protect as many people around the world as possible. All along, we have known that each day matters,” said Stéphane Bancel, chief executive officer of Moderna.
"This positive interim analysis from our Phase 3 study has given us the first clinical validation that our vaccine can prevent COVID-19 disease, including severe disease," Bancel added.
The hopeful news from both companies comes as many European countries are in the middle of a second lockdown to prevent the spread of COVID-19, with hospitals nearly at capacity.
Meanwhile, the US has also seen record high numbers of infections per day, with the country now reaching more than 11 million cases.
Moderna's phase three trials - to determine the vaccine's safety and effectiveness - had enrolled more than 30,000 participants in the US. Pfizer had enrolled more than 43,500 participants.
Representatives from both companies hailed the results as an important "milestone" in their vaccine development.
The Moderna vaccine's efficacy is determined by the appearance of 95 COVID-19 cases among participants, of which 90 cases "were observed in the placebo group versus 5 cases observed" in those who were given the candidate vaccine.
There were 11 severe cases among participants who were given a placebo and none among those who had received two vaccine doses.
This efficacy could change however as trials continue and more COVID-19 cases are recorded among participants.
The vaccine's side effects were generally "mild or moderate" and included pain at the injection site, fatigue, muscle pain and headache, the company said.
The vaccine is based on new technology that contains mRNA or genetic instructions that help the body to recognise the coronavirus' spike protein -- which it uses to enter the body's cells.
When could the vaccine become available?
Based on the early data, the company will apply for an Emergency Use Authorisation (EUA) with the US Food and Drug Administration (FDA) and will submit applications to global regulatory agencies.
That US process authorisation process could take two months. Moderna said it was on track to develop 500 million to 1 billion doses globally in 2021.
British Health Secretary Matt Hancock swiftly announced that the country has signed an agreement with the US company for 5 million doses "when it comes on stream in spring next year", adding to the 40 million doses it secured from Pfizer and BioNTech.
The European Medicines Agency announced Monday that it started a "rolling review" of the Moderna vaccine which will continue "until enough evidence is available to support a formal marketing authorisation application."
The EU currently has five vaccine contracts after announcing an agreement to buy up to 405 million doses of the candidate vaccine produced by European company CureVac. European Commission President Ursula von der Leyen said that the EU was working on a sixth contract with Moderna.
In an interview with Euronews, Dan Staner, Vice-president and Head of EMEA region at Moderna said that a deal with the EU could be signed within the next week to two weeks.
"We're having very good conversations with the European Commission and the European tender, so we hope as soon as possible, so if tomorrow that would be the best, tomorrow will be the best opportunity," he said. "So, on our side, those conversations continue and have been extremely active in the last couple of weeks".
Pressed for a timescale, he said: "I believe, that's my best guess, probably in the next one to two weeks probably we'll come to a conclusion with the European Union".
Pfizer forecast last week production of 50 million doses in 2020 and up to 1.3 billion in 2021. The EU announced a deal for 300 million doses of Pfizer's experimental coronavirus vaccine after news broke about its efficacy.
"If all goes well and of course this is pending authorisation by the European Medicine's Agency once they submit to be authorised, we would expect that we could possibly have vaccines available, possibly end of 2020, beginning 2021," said EU Commissioner for Health Stella Kyriakides just last week.
Kyriakides tweeted on Monday that the news from Moderna was once again "encouraging" and that the EU was "doing everything we can to secure safe & effective vaccines."
At a press conference at the World Health Organization on Monday, Assistant Director-General Dr Mariângela Simão also said the Moderna results were "positive" and "promising".
"We are very happy to hear positive results but there are many vaccine candidates coming up with results before the end of this year and the beginning of next year, and some will be easier to implement on country level but some will be more challenging," she said.
"But overall, we see the landscape is very, very promising so far in the fact that we have already two vaccine candidates that are showing interim results at 90, 94.5 per cent efficacy. It is quite encouraging".
Her colleague, WHO Chief Scientist Dr Soumya Swaminathan cautioned that the rollout of any potential vaccine would take time.
"We are looking at at least the first half of next year as being a period of very, very limited doses. Supplies are going to be limited. There are bilateral deals that companies have done. So many of the doses have already been booked by some countries," she said.
"We are hoping there will be enough in the [WHO's covax] facility so that the AMC [Advance Market Commitment] countries - the 92 countries in the AMC group - will also get access to these doses at the same time but right now, it is just a question of planning: week by week and day by day".