Scientists from a range of Chinese research institutions found the vaccine candidate provoked a double immune response by stimulating two types of antibodies and also T-cells.
The second phase of testing was conducted over the course of April, and aimed to evaluate the immune response, safety and determine the most suitable dose for a third round of trials.
Because there is still no universally successful Covid-19 therapy, participants were not deliberately exposed the virus.
As a result, it is still unclear whether the level of immune response provided by the vaccine is sufficient to protect against infection.
NEW—Chinese phase 2 trial finds #COVID19 vaccine is safe and induces an immune response https://t.co/y19Tg7VmUT pic.twitter.com/olXJsOgTFv
Advertisement— The Lancet (@TheLancet) July 20, 2020
During the trial, 253 people received a high dose of the vaccine, 129 received a low dose, while 126 were given a placebo.
The research, published in The Lancet, found 95% of participants in the high-dose group and 91% of the low-does group showed either antibody or T-cell immune response 28 days after vaccination.
These two immune responses work together to resist infection – antibodies are found in bodily fluids and tackle viruses by either neutralising them or binding to them to flag them up to other immune cells.
T-cells can recognise and kill a cell that has been hijacked by a virus and turned into a little factory generating new viruses – acting as a backstop if viruses do manage to get past the antibodies.
The study found:
– The vaccine generated a neutralising antibody response in 59% of high-dose and 47% of low-dose participants,
– It generated a binding antibody response in 96% of the high-dose and 97% of the low-dose group,
– The participants in the placebo group showed no antibody increase from baseline,
– T-cell responses were found in 90% of the high-dose participants and 88% of the low-dose participants,
– Twenty-four people in the high-dose group had a severe reaction to the vaccine, one in the low-dose group and two people in the placebo group – the most common severe reaction was fever.
It is possible that an additional dose may be needed in order to induce a stronger immune response in the elderly population, but further research is under way to evaluate this
Professor Feng-Cai Zhu, of China’s Jiangsu Provincial Centre for Disease Control and Prevention, said: “This is an important step in evaluating this early-stage experimental vaccine and phase-three trials are now under way.”
Just 13% of those involved were over the age of 55, and the third round of testing is expected to include much greater numbers of older people.
Professor Wei Chen, from the Beijing Institute of Biotechnology, says: “Since elderly individuals face a high risk of serious illness and even death associated with Covid-19 infection, they are an important target population for a Covid-19 vaccine.
“It is possible that an additional dose may be needed in order to induce a stronger immune response in the elderly population, but further research is under way to evaluate this.”
The researchers also emphasised it is not clear if any immune response may last, as participants were last tested just 28 days after receiving their dose of the vaccine.
