China’s CanSino Biologics, the world’s first company to kick start clinical trials of a vaccine in Wuhan for SARS-CoV-2, the causal of COVID-19. The vaccine makes use of a genetically engineered adenovirus for delivering SARS-CoV-2 spike protein gene into human cells. Researchers believe that the vaccine can train our immune systems to avoid infection from a real virus. The Phase I study included 108 people injected with the vaccine, and many of them developed immune responses. Scientists differentiate between the antibodies that bind to the spike protein and the one that prevents infection known as neutralizing antibodies.
The vaccine carries Ad5 adenovirus that causes the common cold. In Cansino’s study, around 50 per cent of the people with a history of infection with Ad5, developed neutralizing antibodies targeting Ad5 itself.
Higher doses of the vaccines can tackle the problem of developing the Ad5 neutralizing antibodies. But high doses of adenoviral vectors can be toxic. Therefore, CanSino decided not to proceed with the high dose due to safety concerns. However, the company has started its Phase II trials in April, comprising 500 people.
The DownsideAround 81 per cent of the people who took part in the study, reported an adverse reaction within seven days after the vaccination (Lancet, 2020). The major side effects include headache, muscle pain, fatigue, and fever. Among all the participants, nine suffered from a severe fever which may be because of viraemia caused by Ad5 vector infection.
It is also worth mentioning that till today, vaccines based on adenoviral vector didn’t work out for humans but has worked for wild animals in preventing the spread of rabies.
CanSino is a China-based company and was the first to publish its result in a peer-reviewed Journal. Apart from China, The US government is funding Johnson & Johnson and AstraZeneca for developing adenoviral vector vaccines. The vaccine race is on, and of all, China is desperate to win.