People who already have immunity to the viral vector of the vaccine produce worse antibodies. But how this will affect the protective properties of the vaccine, only further studies can show.
Friday, May 22, a magazine 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. Testimonials from some leading scientists Stat news,
In the manufacture of the vaccine (manufacturer - CanSino Biologics), scientists used an adenoviral vector. That is, a portion of the SARS-Cov-2 virus genome was delivered to the human body by attenuated type 5 adenoviruses (Ad5). The study showed that people who had immunity against Ad5 before vaccination might have difficulty developing immunity against COVID-19. In addition, in such people, after vaccination, the concentration of antibodies to Ad5 increased. That is, immunity "considered" the vaccine as a means of enhancing immunity against Ad5.
Immunity "busy" with adenovirus
“Definitely, this is one of the biggest problems with using vector vaccines that people could previously be immune to,” said Michael Mina, an epidemiologist of infectious diseases at the School of Public Health T.H. Chan 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 a reaction 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 located in the adenoviral vector."
This is unlikely to become a vaccine for the elderly.
Problems that are related to immunity to Ad5 were more likely to be experienced by participants aged 45-60. Stat recalls that in some populations, immunity to this virus can occur in 70% of cases.
“It probably won’t be the vaccine you would like to give to people over 65 because they may have a higher level [имевшегося иммунитета]“, Said Kathryn Edwards, director of Vanderbilt University's vaccine research program, to Stat News.
Will the vaccine give a sufficient titer of antibodies?
The results of the study were predictable by Gary Kobinger, director of the Center for the Study of Infectious Diseases at the University of Laval. He noted that he did not expect this vaccine to be successful.
Cobinger recalled that CanSino was testing an Ebola vaccine with the same vector, and the problem of existing immunity against adenovirus was known. Manufacturers have suggested that it can be circumvented by using a high dose of the vaccine or by changing the route of administration (for example, with nasal use). But CanSino has already reported that a high dose vaccine will not be used in a phase II study.
In the group of participants with existing immunity against Ad5, 28 days after the introduction of the vaccine, the number of antibodies against coronavirus increased four times in 25% of cases (5 people) when using a low dose of the vaccine and 37% (7 people) after the average dose. Katherine Edwards notes that this data is a cause 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 HIV vaccine test, which was based on this principle, was stopped in 2007. For an unknown reason, people who were vaccinated were more likely to become infected during the phase III study. The authors of the study of the vector vaccine against COVID-19 indicate that they remember the possibility of such complications and are going to monitor them.