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Experimental COVID-19 vaccine gets mixed reviews from scientists
People who are already immune to the viral vaccine vector are less likely to produce antibodies. But how this will affect the protective properties of the vaccine, only further research can show.
Photo: Tristan Truesdell
On Friday, May 22, The Lancet published a Phase I clinical trial report of the first SARS-CoV-2 coronavirus vector vaccine. This publication caused a mixed reaction in the scientific community. Some leading scientists are quoted by Stat News.
First vector vaccine for COVID-19 shows effect in early phase of human study
This is the first full publication of the results of an experimental vaccine against the SARS-CoV-2 coronavirus.
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In the manufacture of a vaccine (manufacturer - CanSino Biologics), scientists used an adenoviral vector. That is, a section of the genome of the SARS-Cov-2 virus was delivered to the human body by weakened type 5 adenoviruses (Ad5). The study found that people who had immunity against Ad5 prior to vaccination may have difficulty developing immunity against COVID-19. In addition, the concentration of antibodies to Ad5 increased in such people after vaccination. That is, the immunity "viewed" the vaccine as a means of enhancing immunity against Ad5.
Immunity "occupied" by adenovirus
“This is definitely one of the biggest challenges with vector vaccines that humans may have previously been immune to,” Michael Mina, an infectious disease epidemiologist at the T.H. School of Public Health, told Stat News. Chan of Harvard University.
Mina explained that the existing immunity against the viral vector poses a risk that the immune response may be "skewed" in favor of the response to known antigens (antigens of the viral vector). Then immunity "does not focus so much on a new aspect, which in this case should be the coronavirus proteins placed in the adenovirus vector."
It is unlikely to be a vaccine for the elderly
Problems related to Ad5 immunity were more common among participants aged 45-60. Stat recalls that in some populations, immunity to this virus can occur in 70% of cases.
Scientists criticized the publication on the intermediate successes of the first vaccine against COVID-19
Experts believe that the published data do not allow judging even the early criteria for the effectiveness of the vaccine.
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“It probably won't be the vaccine you would like to give to people over the age of 65, as they may have a higher level of [existing immunity],” Kathryn Edwards, director of the Vanderbilt University Vaccine Research Program, told Stat News.
Will the vaccine produce a sufficient antibody titer?
Gary Kobinger, director of the Center for Infectious Diseases Research at Laval University, called the results predictable. He noted that he did not expect this vaccine to be successful.
Kobinger recalled that CanSino tested the Ebola vaccine with the same vector, and the problem of existing immunity against adenovirus was known. Manufacturers assumed that it could be circumvented by using a high dose of the vaccine or by changing the route of administration (for example, nasal use). But CanSino has already announced that the high dose vaccine will not be used in the Phase II study.
In the group of participants with existing immunity against Ad5, 28 days after the vaccine was administered, the number of antibodies against coronavirus quadrupled in 25% of cases (5 people) with a low dose of the vaccine and 37% (7 people) after a medium dose. Catherine Edwards notes that this data is a reason for caution. But she adds that today it is not known what concentration of antibodies is required to protect against coronavirus. It cannot be ruled out that even in this group of patients it will be sufficient; further studies will show this.
The trial of a vaccine against HIV infection, which was based on this principle, was stopped in 2007. For some unknown reason, people who were vaccinated were more likely to become infected with HIV during the Phase III study. The authors of the study of the vector vaccine against COVID-19 indicate that they are aware of the possibility of such complications and are going to monitor them.