by Xinhua writer Zhang Jiawei

LONDON, May 22 (Xinhua) -- China's COVID-19 vaccine trial, the first such vaccine to reach phase 1 clinical trial, has been found to be safe, well-tolerated, and able to generate an immune response against SARS-CoV-2 in humans, according to a study published online Friday by the medical journal The Lancet.

The open-label trial in 108 healthy adults demonstrates promising results after 28 days and the final results will be evaluated in six months, The Lancet said in a press statement.

Further trials are needed to tell whether the immune response it elicits effectively protects against SARS-CoV-2 infection, said the medical journal.

During the 73rd session of the World Health Assembly ealier this week, China pledged to make the country's COVID-19 vaccine a global public good when available.

"These results represent an important milestone. The trial demonstrates that a single dose of the new adenovirus type 5 vectored COVID-19 (Ad5-nCoV) vaccine produces virus-specific antibodies and T cells in 14 days, making it a potential candidate for further investigation," said Professor Wei Chen from the Beijing Institute of Biotechnology in Beijing, China, who is responsible for the study.

"However, these results should be interpreted cautiously. The challenges in the development of a COVID-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from COVID-19. This result shows a promising vision for the development of COVID-19 vaccines, but we are still a long way from this vaccine being available to all," said Chen.

The authors note that the main limitations of the trial are its small sample size, relatively short duration, and lack of randomized control group, which limits the ability to pick up rarer adverse reactions to the vaccine or provide robust evidence for its ability to generate an immune reaction. Further research will be needed before this trial vaccine becomes available to all.

A randomized, double-blinded, placebo-controlled phase 2 trial of the Ad5-nCoV vaccine has been initiated in the central Chinese city of Wuhan to determine whether the results can be replicated, and if there are any adverse events up to six months after vaccination, in 500 healthy adults-250 volunteers given a middle dose, 125 given a low dose, and 125 given a placebo as a control, according to The Lancet.

For the first time, this will include participants over 60 years old, an important target population for the vaccine.

The creation of an effective vaccine is seen as the long-term solution to controlling the COVID-19 pandemic. Currently, there are more than 100 candidate COVID-19 vaccines in development worldwide, according to The Lancet.

"The likelihood of developing a vaccine against SARS-CoV-2 that has some measurable effectiveness and does not have unacceptable side-effects is pretty high although not certain. After all, we have vaccines against most of the infectious diseases where a serious effort has been made to develop them -- most but not all," said Adam Finn, professor of paediatrics at the University of Bristol.

Aside from the vaccine efforts in China, researchers in Britain and the United States are also pushing forward similar trials.

In April, researchers at the University of Oxford have begun vaccine trials on humans. More than 1,000 immunizations for phase 1 trial in healthy adult volunteers have been completed and follow-up is currently ongoing, according to Oxford.

The phase 2 part of the study involves expanding the age range of people the vaccine is assessed in, to include a small number of older adults and children, while phase 3 will see researchers assess how the vaccine works in a large number of people over the age of 18.

"The best-case scenario is that by the autumn of 2020 we have the results about the effectiveness of the vaccine from a phase 3 trial and the ability to manufacture large amounts of the vaccine," professor Sarah Gilbert from the University of Oxford told Xinhua through email in a previous interview.

"But these best-case timeframes are highly ambitious and subject to change," said professor Gilbert, who is one of the scientists leading the COVID-19 vaccine development program at Oxford.

The vaccine used in the Oxford trials is called ChAdOx1 nCoV-19. It is made from a virus (ChAdOx1), which is a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees, that has been genetically changed so that it is impossible for it to grow in humans.

"The clinical studies are progressing very well and we are now initiating studies to evaluate how well the vaccine induces immune responses in older adults, and to test whether it can provide protection in the wider population," Professor Andrew Pollard, head of the Oxford Vaccine Group, said in a statement released Friday by Oxford.

But experts are still cautious when it comes to the development of a viable vaccine.

"What is more difficult to predict is how long it will take to get there and how well the vaccine(s) will work to prevent serious illness and/or prevent infectiousness and how long any such beneficial effects would last after vaccine administration," said Finn. Enditem

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