We are talking about hybrid immunity, which is developed when a person has had a coronavirus, and six months later received a vaccine. There are two main types of immunity: humoral and cellular. In humoral disease, when a virus or vaccine first enters the body, the production of antibodies begins, which eventually disappear, but the immune memory stored in B-cells remains about them. Cellular immunity is provided by T-lymphocytes – T-helpers and T-killers. Helpers activate the killers of viral cells, and the latter destroy them. Helper T cells also activate B cells.
But no matter how effective these two types are, hybrid immunity gives a greater result – it increases the effectiveness of both humoral and T-cell immunities, additionally activating immune B-cells. It also enhances general immune mechanisms that do not depend on the specific variant of the virus.
This was proved first in the UK: in patients who had been ill with coronavirus, and then who were vaccinated, the level of antibodies was higher than in those who did not get sick, but who even received two doses of the vaccine. Later in the United States, it was confirmed that in such patients the level of antibodies can be 100 times higher than in those who had been ill, but not vaccinated, and 25 times higher than in simply vaccinated.
Scientists are also interested in whether hybrid immunity is developed in people who were first vaccinated and then ill. It is noted that such studies have not yet been carried out.