Hopes grow of a potential vaccine for the novel coronavirus after two trials, each by British and Chinese researchers, showed most volunteers had developed widespread antibody immune response.
Two coronavirus vaccine candidates have proven safe for humans and produced strong immune reactions among patients involved in separate clinical trials.
The first trial among more than 1,000 adults in Britain found that the vaccine induced "strong antibody and T cell immune responses" against the novel coronavirus, scientists said on Monday.
They said that they found their experimental Covid-19 vaccine produced a dual immune response in people aged 18 to 55 that lasted at least two months after they were immunised.
A separate trial in China involving more than 500 people showed most had developed widespread antibody immune response.
The studies, published in The Lancet medical journal, constitute a major step on the road towards a Covid-19 vaccine that is effective and safe for widespread use.
The authors of the studies said that they encountered few adverse side effects from the vaccine candidates.
However, they cautioned that more research was needed, particularly among older adults, who are disproportionately at risk of dying of coronavirus.
Co-author Sarah Gilbert from the University of Oxford said the results "hold promise."
"If our vaccine is effective, it is a promising option as these types of vaccine can be manufactured at large scale."
British researchers first began testing the vaccine in April in about 1,000 people, half of whom got the experimental vaccine.
Such early trials are usually designed only to evaluate safety, but in this case experts were also looking to see what kind of immune response was provoked.
Dr Adrian Hill, director of the Jenner Institute at Oxford University said how quickly scientists are able to determine the vaccine's effectiveness will depend largely on how much more transmission there is, but estimates they might have sufficient data by the end of the year to decide if the vaccine should be adopted for mass vaccination campaigns.
Hill said Oxford's vaccine is designed to reduce disease and transmission.
It uses a harmless virus — a chimpanzee cold virus, engineered so it can't spread — to carry the coronavirus' spike protein into the body, which should trigger an immune system response.
AstraZeneca making two billion doses
Hill said Oxford has partnered with drugmaker AstraZeneca to produce their vaccine globally, and that the company has already committed to making two billion doses.
AstraZeneca has said it will not seek to profit from the vaccine during the pandemic.
"Even 2 billion doses may not be enough," he said, underlining the importance of having multiple shots to combat the coronavirus.
AstraZeneca is looking to test two high doses of its experimental vaccine against the new coronavirus in later stage trials rather than focus on approval for single or lower doses of the vaccine, its biopharma chief said.
"Right now, the safe thing to do is go with two doses, and then we'll start exploring single doses or lower doses," MenePangalos, executive vice-president for BioPharmaceuticals R&D, told reporters.
UK to buy doses
British politicians have promised that if the shot proves effective, Britons will be the first to get it.
The UK government said it would purchase 100 million doses of the vaccine.
In a statement, the British government said it had secured access to 90 million doses of potential coronavirus vaccines in deals with biotech firms BioNTech, Pfizer and Valneva, the government said Monday.
Prime Minister Boris Johnson said he was "hopeful" of a vaccine, "but to say that I'm 100 percent confident that we will get a vaccine this year or indeed next year is, alas, just an exaggeration."
Also on Monday, Chinese researchers published a study on their experimental vaccine in the Lancet, using a similar technique as the Oxford scientists.
They reported that in their study of about 500 people, an immune response was detected in those who were immunised.
But they noted that because the participants weren't exposed to the coronavirus afterwards, it wasn't possible to tell if they were protected from the disease.
CanSino Biologics' vaccine is made similarly to Oxford’s except the Chinese shot is made with a human cold virus, and the study showed people whose bodies recognised it didn't get as much of the presumed Covid-19 benefit.
Still, China's government already gave special approval for the military to use CanSino's vaccine while it explores final-stage studies.
In an accompanying editorial, Naor Bar-Zeev and William Moss of the Johns Hopkins Bloomberg School of Public Health called both the Oxford and Chinese results "encouraging" but said further judgment should wait until the vaccine is tested on much bigger populations.
READ MORE: China leads Covid-19 vaccine race
Multiple trials under way
Last week, American researchers announced that the first Covid-19 vaccine tested there boosted people's immune systems just as scientists had hoped and the shots will now enter the final phase of testing.
That vaccine, developed by the National Institutes of Health and Moderna, produced the molecules key to blocking infection in volunteers who got it, at levels comparable to people who survived the infection.
The vaccine being developed by Pfizer also works to trigger a similar dual immune response as the Oxford shot.
Pfizer and its German partner BioNTech also released an encouraging Phase 1 report on Monday.
Nearly two dozen potential vaccines are in various stages of human testing worldwide, with a handful entering necessary late-stage testing to prove effectiveness.