Discovering the secret of the power of hybrid immunity in the battle of “Covid-19”

People who were infected with the “emerging corona virus” before vaccination generate a more specific immune response to fight viral infections, and produce broader antibodies than people for whom the only protection is the vaccine, according to a study by researchers at the University of Washington School of Medicine published in the journal “Cell” on March 23 ( March) current. “Vaccines alone work very well in protecting against disease, but they do not generate an immune response as diverse as the infection followed by vaccination,” said Marion Pepper, assistant professor in the Department of Immunology at the University of Washington, who led the research team in a report published on the university’s website in conjunction with the publication of the study. .

Immunity against the virus can be acquired in two ways, either through infection or by obtaining a vaccine. The first is called “naturally acquired immunity,” and the second is “vaccine-acquired immunity,” but if you become infected and then receive the vaccine, it is “hybrid immunity.” Previous research indicated that “hybrid immunity” provides better protection against the virus than either naturally acquired or vaccine-acquired immunity. In the new study, the researchers sought to find out why, comparing differences in the immune response to the virus over three doses of the vaccine in 30 people who were previously infected, and in 24 people who were vaccinated but never infected.

They found that after vaccination, those who had previously been infected were born from memory B cells, which generate antibodies that can neutralize the virus and prevent infection.

The memory B cells in people with hybrid immunity also produced a variety of antibodies that could neutralize not only the original strain of the virus, but also modern variants such as delta and omicron. “Even if the first infection was caused by the first strain, the Wuhan strain, and the vaccine they received was based on that strain, people with hybrid immunity were able to produce neutralizing antibodies against all species,” says Pepper.

Hybrid immunity also generated a more specific cellular immune response to fight viral infections, called the Th1 response. In this response, CD4+ T cells release inflammatory signals, specifically a cytokine called interferon-gamma, which is an antiviral. “While additional vaccination can increase the number of CD4+ T cells in those who have not been infected to levels similar to those who have been infected, it cannot generate the same type of response seen in those with hybrid immunity,” says Pepper. ».

Several factors can explain why hybrid immunity appears to be more robust. Time may simply be one factor. After exposure to pathogens, immune cells in the lymph nodes improve the immune response, and this process of immune maturation generates bodies and cells that are more effective against new infections.

In the case of the hybrid immune group, a year passed from infection to receiving the vaccine, on the other hand, individuals in the vaccine group only received their second dose only a few weeks after the first dose, giving the immune system much less time to improve its response. Another factor may be where the immune system first interacts with the invading pathogen, as the immune cells of the study participants with hybrid immunity first encountered the virus in the lungs and nasal passages, by contrast, only the cells of the vaccine group encountered the viral protein in muscle where she received the vaccine.

“It is possible that exposure in the lungs and mucosal tissues such as those in the nasal passages generates a better immune response to respiratory pathogens because cells can be better retained in these locations,” says Pepper. “Our findings could help design vaccines that take advantage of this effect, such as those that can be administered into the nasal passages or inhaled into the lung,” she says.