Hopes of getting a Covid-19 vaccine were raised today after Moderna's experimental jab was proven to trigger an immune response in all 45 injected volunteers.
Researchers also found the jab — one of the front-runners in the global coronavirus vaccine race — was safe and no participants suffered any serious side effects.
But more than half reported mild or moderate reactions such as fatigue, headache, chills, muscle aches or pain at the injection site. Scientists said side effects were a 'small price to pay' for protection against Covid-19.
'No matter how you slice this, this is good news,' said Dr Anthony Fauci, the US government's top infectious disease expert.
Massachusetts-based Moderna was the first US company to start human testing of a vaccine for the novel coronavirus on March 16, 66 days after the genetic sequence of the pathogen was released.
It's now preparing to start a 30,000-person trial later this month to prove the vaccine really is strong enough to protect against the coronavirus.
Scientists around the world are still desperately rushing to find a vaccine, which is considered crucial to unlocking the economy and ending the pandemic, which has killed almost 600,000 people worldwide since January.
It comes after a leading British scientist behind another experimental jab developed at Imperial College London claimed that a Covid-19 vaccine could be ready within a year if trials go well. And Oxford University's candidate is showing positive signs it could work, it was claimed today.
Moderna's experimental coronavirus vaccine triggered an immune response and only resulted in mild side effects in a trial of 45 healthy volunteers, according to results published Tuesday
'The world urgently needs vaccines to protect against Covid-19,' said Dr Lisa Jackson of Kaiser Permanente Washington Health Research Institute in Seattle and lead author of the study.
The US federal government is supporting Moderna's vaccine with nearly half a billion dollars in funding.
A successful Covid-19 jab could be a turning point for Moderna, which has never had a licensed product.
Moderna's vaccine, known as mRNA-1273, makes use of ribonucleic acid (RNA).
RNA is a chemical messenger in human bodies that contains instructions for making proteins.
The genetic material travels throughout the body's cells, giving final instructions on which proteins to build.
When lab-manufactured pieces of mRNA are injected into people, the hope is that the cells would take in the genetic snippets, make viral proteins and trigger an immune response against the SARS-CoV-2 virus, which causes Covid-19.
The vaccine instructs cells to make proteins that mimic the outer surface of the coronavirus.
This then trains the body to recognise these as a foreign invader, and mount an immune response against it.
The results, published in the prestigious New England Journal of Medicine, involved three groups of 15 volunteers aged 18-55.
The groups tested 25, 100 or 250 micrograms of the vaccine. Everyone got two doses, 28 days apart.
The team reported that individuals who got two doses of the vaccine had high levels of virus-killing neutralizing antibodies that exceeded the average levels seen in people who had recovered from Covid-19.
Neutralizing antibodies are able to kill the virus themselves, rather than just tagging it for other immune cells to attack.
Adverse events after the second dose occurred in seven of the 13 volunteers who got the 25-microgram dose.
However, all 15 participants who received the 100 microgram dose and all 14 who got the 250 microgram dose had adverse side effects.
In the highest-dose group, three patients had severe reactions such as fever, chills, headache or nausea. One of these had a fever of 103.3F (39.6C).
'We didn't see any events that are characterized as serious adverse events,' Dr Jackson said, referring to reactions that require hospitalisation or result in death.
'It's a good first step,' said Dr William Schaffner, a vaccine expert at Vanderbilt University Medical Center who was not involved in the study.
'There's nothing here that would inhibit one from going ahead to the Phase 2/Phase 3 trials,' he said.
'A little fatigue and headache and myalgia (muscle pain) and pain at the injection site is a small price to pay for protection against Covid-19.'
Dr Fauci called the findings 'good news', adding that testing will be expanded to include older adults, as well as people with chronic health conditions that make them more vulnerable to the virus — and Black and Latino populations.
The NIH-led Phase 1 study has been expanded to an additional six cohorts, involving adults aged above 56 who are more at risk of serious disease.
Moderna said it will follow the volunteers for a year after the second shot, to look for side effects and check how long immunity actually lasts.
A phase 2 trial of the vaccine, in 600 healthy adults, evaluating doses of 50 micrograms and 100 micrograms, is ongoing, having started dosing on May 29.
The final stage of testing (Phase III) will begin recruiting this month. It will be randomised and placebo-controlled, enrolling about 30,000 participants in the US.
Participants will receive a dose of 100 micrograms, Moderna said, to minimize adverse reactions.
At that dose, Moderna said the company is on track to deliver about 500million doses per year, and possibly up to one billion doses per year, starting in 2021, from the company's internal US manufacturing site and strategic collaboration with Swiss drugmaker Lonza.
However, the company said in March a commercially-available vaccine is not likely to be available for at least 12-18 months, but healthcare professionals may be able to access it from the fall of this year.
Efforts to produce the vaccine have been scaled up across the world, and as of July 14, there are 23 candidate vaccines in clinical evaluation, according to the World Health Organization. A further 140 are in the preclinical evaluation stage to see if they are safe to use.
Two leading vaccine candidates come from British scientists at University of Oxford and Imperial College London.
Professor Robin Shattock, who leads a team working to produce a vaccine at Imperial College London, said theirs could be ready within a year if trials go 'really well'.
Speaking on Sky News' Sophie Ridge On Sunday, Professor Shattock said: 'So we anticipate if everything goes really well that we'll get an answer as to whether it works by early next year.
'And we have put in place the infrastructure to make that vaccine for the whole of the UK.
'So, assuming that the funding is there to purchase that vaccine, we could have that vaccine rolled out across the UK in the first half of next year.'
Fifteen volunteers have already been given the trial vaccines and testing is expected to ramp up to include as many as 200-300 new participants in the coming weeks.
Clinical trials of the University of Oxford vaccine candidate were put into motion in April and might finish by September.
Phase III, or final-stage, trials are under way involving thousands of people in the UK as well as Brazil and South Africa where the virus is circulating more.
The science behind both British vaccine attempts hinges on recreating the 'spike' proteins that are found all over the outside of the Covid-19 virus.
Both will attempt to recreate or mimic these spikes inside the body. The difference between the two is how they achieve this effect.
Imperial College London will try to deliver genetic material (RNA) from the coronavirus — similar to Modernas.
The RNA programs cells inside the patient's body to recreate the spike proteins. It will transport the RNA inside liquid droplets injected into the bloodstream.
The team at the University of Oxford, on the other hand, will genetically engineer a virus to look like the coronavirus - to have the same spike proteins on the outside - but be unable to cause any infection inside a person.
This virus, weakened by genetic engineering, is a type of virus called an adenovirus, the same as those which cause common colds, that has been taken from chimpanzees.
If the vaccines can successfully mimic the spikes inside a person's bloodstream, and stimulate the immune system to create special antibodies to attack it, this could train the body to destroy the real coronavirus if they get infected with it in future.
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