According to a new research published in The Lancet, the early-stage trial was conducted by researchers at several laboratories and included 108 participants aged 18 to 60.
A report on The New York Times, indicates that those who received a single dose of the vaccine produced certain immune cells, called T cells, within two weeks. Antibodies needed for immunity peaked at 28 days after the inoculation.
The trial is the first step in testing the vaccine and was intended mainly to verify its safety.
In proving the effectiveness of the vaccine, trials will have to been taken in large numbers, maybe few thousands, or perhaps hundreds of thousands and even more people.
A vaccine for COVID-19 is considered to be the best long-term solution for allowing countries to reopen their economies and return to normalcy.
American business magnate, Bill Gates, had said it could take as long as two years or at least nine months before a vaccine can be found to tackle the deadly coronavirus pandemic that has claimed thousands of lives across the globe.
Mr Gates said as of April 9, 115 different COVID-19 potential vaccines were being developed globally.
The vaccine reported on Friday was made with a virus, called Ad5, modified to carry genetic instructions into a human cell.
The cell begins making a COVID-19 protein; the immune system learns to recognise the protein and attack it, in theory preventing the virus from ever gaining a foothold.
But Ad5 is a cold virus that many people probably have already been exposed to. About half of the participants in the trial had powerful antibodies to Ad5 before they got the vaccine.
In these people, “their immune systems will essentially rear up and blunt the effect of the vaccine,” said Kirsten Lyke, a vaccinologist at the University of Maryland who is leading another COVID-19 vaccine trial.
The researchers in China did find that people who had Ad5 antibodies were less likely to develop a strong immune response to the vaccine.
Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, said
That may limit the use of this vaccine.
“If you are comparing vaccines, the adenovirus ones so far seem to be on the lower end of the spectrum.”
Other teams have turned to adenoviruses to develop COVID-19 vaccines, but they are using less common strains, or even animal strains, to circumvent this problem.
Only a subset of people in the new trial produced neutralizing antibodies to th. virus, the kinds of molecules needed for immunity. Other vaccine candidates have reported better results in the levels of neutralising antibodies.
People between 45 and 60 years of age are said to have produced weaker immune responses following vaccination than younger participants.
Ms Lyke said the responses may turn out to be even weaker among people older than 60.
“That’s a very important target population that they would have to examine,” she said.
Ms Lyke suggested that this vaccine might be best suited to younger populations and children.
The results are based on data from a short period, and it is unclear how long the vaccine’s protection might last.
The researchers tested three doses and said the highest dose seemed to be the most effective.
Experts said this dose-response is encouraging. Unfortunately, people who got the highest dose also experienced the most side effects.
About 80 per cent of the participants reported at least one side effect, all expected with a viral vaccine, experts said.
Apart from pain at the injection site, close to half of the participants reported fever, fatigue and headaches, and about one in five had muscle pain.
Experts praised the researchers for publishing all of their data for others to review and said the results were promising overall.
“What we hope is that there will be not one vaccine but several vaccines that will be approved,” Mr Barouch said.
He said the world needs multiple vaccines.