CanSino Biologics, a Chinese vaccine firm became the world's first company on March 16 to start a clinical trial study of potential Coronavirus vaccine. Within 10 weeks, the firm again achieves a milestone by sharing peer-reviewed data assessing the safety and immunogenicity of a SARS-CoV-2 vaccine, beating US firm Moderna, which did not share such data.
Last week, Chinese biotechnology firm CanSino Biologics said in its phase 1 trial of COVID-19 vaccine, an immune response in 108 people was recorded and that the level of response was underwhelming. "It is not great, but it is better than nothing," said vaccine researcher Hildegund Ertl.
This is close on the heels of a similar announcement by US biotechnology company Moderna that claimed its vaccine has shown tentatively positive results. The vaccines are, however, different. Moderna's is a messenger-RNA vaccine based on unproven technology, whereas CanSino's uses a genetically engineered adenovirus, with better-understood characteristics. Moderna has not shared its data though it made its results public in a press release.
It should be noted that the vaccine uses an adenoviral vector, which us a genetically engineered adenovirus. This is used to deliver the gene which encodes the novel Coronavirus spike protein into human cells. As per the scientists, they are hoping that the spike proteins generated from the Chinese vaccine will give the immune systems some target practice to quickly halt an infection of the real virus.
The Chinese government approved the CanSino's Ad5-based Ebola vaccine, for emergency use and national stockpiling in 2017 which was only tested in a Phase II study. Adenoviral vector vaccines, which are not proven to work on humans, got the only approval outside China by the Canadian government to prevent the spread of rabies in wild animals. But recently the National Research Council of Canada stated that it would begin manufacturing CanSino's COVID-19 vaccine.
Clinical trials of the vaccine are expected to begin soon in Canada, which would make it the most advanced COVID-19 vaccine program in that country.
The study by CanSino Biologics
It should be mentioned that in the Phase I safety study, the Chinese researchers had given three doses of the vaccine to 108 people. Later, they noticed that most of the participants have developed immune responses, which was measured by the levels of antibodies and T cells that target the spike protein.
But scientists claimed that developing neutralizing antibodies, which defend a cell from a pathogen, is a crucial step that human bodies should take to prevent the virus from gaining a foothold in the first place.
The study published in The Lancet, showed that about 75 percent of people who received the high dose of CanSino's vaccine and 50 pecent of people who received a medium or low dose of the vaccine developed levels of neutralizing antibodies deemed high by the researchers
Dennis Burton, an immunologist at Scripps Research said what levels of neutralizing antibodies are needed to protect from novel Coronavirus infection, remain to be decided yet. He also added that the levels induced by this particular Chinese vaccine "are not overwhelming by any means at all."
Hildegund C.J. Ertl, a scientist who develops and studies adenoviral vector vaccines at the Wistar Institute in Philadelphia, explained that the antibody responses are "a little disappointing," especially in the oldest participants in the research program, aged between 45 and 60, who are less likely to develop neutralizing antibodies.
Problems with the Chinese vaccine candidate
It should be noted that the CanSino's vaccine is based on a prevalent adenovirus, known as Ad5 which causes the common cold. It was noticed that people infected with Ad5 developed high levels of neutralizing antibodies that target Ad5 which includes half the people in the recent study who were less likely to have a strong antibody response to the CanSino's vaccine.
Even though, it is possible that a higher dosage of the vaccine can overcome the Ad5 neutralizing antibodies, as per Ertl the increased level of vaccine dosages can be toxic. However, understanding the safety issues using high doses, the Chinese firm decided to drop the idea to increase the vaccine doses. Currently, the vaccine company is working on its Phase II study including 500 people, who are being administrated with low and medium doses.
It should be mentioned that around 81 percent of the participants have experienced vaccine side effects such as headache, muscle pain, fatigue, and fever. As per Ertl, nine participants had shown signs of severe fevers, including five people who received a high dose of the vaccine.
