(Yicai Global) May 25 -- Shares of China's CanSino Biologics slumped despite the promising results of the world's first concluded phase one trial of a Covid-19 vaccine as investors took in profits after the reliability of the study raised some concerns.

CanSino's stock price [HK: 6185] surged more than 7 percent in the morning but fell back nearly 20 percent to HKD178.50 (USD23) in the afternoon. The price has tripled this year, prompting US J.P. Morgan Chase and Los Angeles-headquartered Capital Group hike their stakes several times, according to news outlet 36Kr.

The adenovirus type 5 vectored Covid-19 vaccine has generated neutralizing antibodies and T-cell responses in healthy adults in a study conducted in Wuhan, the early epicenter of the pandemic, according to an article published on The Lancet on May 22.

However, some half of the participants already had pre-existing immunity to the inactivated virus that the vaccine contained, which could compromise some of the results.

Still, the Tianjin-based company forges ahead with phase two, started last month, which includes adults older than 60 years of age.

Drug firms around the world have raced to come up with a product to protect people against the new type of coronavirus. On May 18, US Moderna disclosed preliminary results of its first trial phase, causing a stock price rally.

T-cell responses were noted 14 days after the inoculation, and humoral responses peaked at day 28, meaning that in 28 days all vaccine takers should be protected, the Chinese biomedicine company revealed about the study that included 108 participants. But the vaccine "warrants further investigation," it added.

Trial participants received low, mid-level, or high doses of the experimental vaccine and the lower doses seemed the safest. The most common side effects were fever, fatigue, headache, and muscle pain.

The vaccine maker has joined hands with Co & Institute Of Biotechnology and China's Academy Of Military Medical Sciences to develop the inoculation.

Editor: Emmi Laine