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According to new research published in The Lancet, the open-label trial in 108 healthy adults demonstrates promising results after 28 days.
The first vaccine against covid-19 that has reached phase 1 of the clinical trial is safe, well tolerated and capable of generating an immune response against SARS-CoV-2 in humans, according to new research published in the journal ' The Lancet'. The open-label trial in 108 healthy adults demonstrates promising results after 28 days. The final results will be evaluated in six months. In any case, more trials are needed to know if the immune response it provokes effectively protects against SARS-CoV-2 infection.
"These results represent an important milestone. The trial demonstrates that a single dose of the new adenovirus type 19 vectored covid-5 vaccine (Ad5-nCoV) produces specific antibodies against the virus and T cells in 14 days, making it a potential candidate for further investigation," explains the person responsible for the work, Wei Chen, from the Beijing Institute of Biotechnology (China).
"However, these results should be interpreted with caution. The challenges in developing 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 very far from this vaccine being available to everyone," the scientist points out. Currently, there are more than 100 Covid-19 vaccine candidates in development around the world.
The new Ad19-vectored covid-5 vaccine evaluated in this trial is the first to be tested in humans. It uses a weakened common cold virus (adenovirus, which easily infects human cells but is unable to cause disease) to deliver genetic material encoding the SARS-CoV-2 spike protein to cells. These cells produce the spike protein and travel to the lymph nodes, where the immune system creates antibodies that recognize that spike protein and fight the coronavirus.
The trial evaluated the safety and ability to generate an immune response of different doses of the new Ad5-nCoV vaccine in 108 healthy adults between 18 and 60 years of age who were not infected with SARS-CoV-2. Volunteers from a center in Wuhan, China, were enrolled and assigned a single intramuscular injection of the new Ad5 vaccine at a low, medium, or high dose.
The researchers tested the volunteers' blood at regular intervals after vaccination to see if the vaccine stimulated both arms of the immune system: the body's "humoral response" (the part of the immune system that produces neutralizing antibodies that can fight infection and which could offer a level of immunity), and the cell-mediated arm of the body (which relies on a group of T cells, rather than antibodies, to fight the virus). The ideal vaccine could generate both antibody and T cell responses to defend against SARS-CoV-2.
The vaccine candidate was well tolerated at all doses, with no serious adverse events reported within 28 days of vaccination. Most adverse events were mild or moderate, with 83 percent (30/36) of those receiving low and medium doses of the vaccine and 75 percent (27/36) in the high-dose group reporting at least one adverse reaction within 7 days of vaccination.
Two weeks after vaccination, all dose levels of the vaccine triggered some level of immune response in the form of agglutinating antibodies (which can bind to the coronavirus but do not necessarily attack it - low dose group 16/36, 44%; medium dose 18/36, 50%; high dose 22/36, 61%), and some participants had detectable neutralizing antibodies against SARS-CoV-2 (low dose group 10/36, 28%; medium dose 11/36 , 31%; high dose 15/36, 42%).
After 28 days, most participants had a fourfold increase in binding antibodies (35/36, 97% in the low-dose group; 34/36 (94%) in the medium-dose group; and 36/36, 100% in the low-dose group. high dose), and half (18/36) of the participants in the low and medium dose groups and three quarters (27/36) of those in the high dose group showed neutralizing antibodies against SARS-CoV-2 .
The Ad5-nCoV vaccine also stimulated a rapid T cell response in most volunteers, which was greatest in those receiving the highest and middle doses of the vaccine, with levels peaking at 14 days. vaccination (low dose group (30/36, 83,3%), medium dose group (35/36, 97,2%) and high dose group (35/36, 97,2%) at 14 days).
Further analyzes showed that 28 days after vaccination, the majority of recipients showed a positive T cell response or had detectable neutralizing antibodies against SARS-CoV-2 (low dose group 28/36, 78%; medium dose 33/36, 92%; high dose group 36/36, 100%).
However, the authors point out that both antibody and T cell responses could be reduced by high pre-existing immunity to adenovirus type 5 (the vector/carrier of the common cold virus); In the study, between 44 and 56 percent of trial participants had high pre-existing immunity to adenovirus type 5 and had a less positive antibody and T cell response to the vaccine.
"Our study found that pre-existing immunity to Ad5 could slow down rapid immune responses to SARS-CoV-2 and also reduce the peak level of responses. Furthermore, high pre-existing immunity to Ad5 could also have a negative effect on persistence of immune responses elicited by the vaccine," says Feng-Cai Zhu of China's Jiangsu Provincial Center for Disease Control and Prevention, who led the study.
The authors note that the main limitations of the trial are the small sample size, the relatively short duration and the lack of a randomized control group, which limits the ability to detect rarer adverse reactions to the vaccine or to provide robust evidence. of its ability to generate an immunological reaction. More research will be needed before this trial vaccine is available to everyone.
A randomized, double-blind, placebo-controlled phase 2 trial of the Ad5-nCoV vaccine has begun in Wuhan to determine if the results can be reproduced, and if there are any adverse events up to 6 months after vaccination, in 500 adults healthy, 250 volunteers who were given a medium dose, 125 who were given a low dose and 125 who were given a placebo as a control. For the first time, this will include participants over the age of 60, an important target population for the vaccine.
