Cell: Improving cellular responses and mixed immunity

People who were infected with SARS-CoV-2 before being vaccinated developed a more specific immune response and produced a more Broad antibody response

"Vaccines alone are very good at preventing disease; they just don't produce as diverse an immune response as a post-vaccination infection," said Marion Pepper, an associate professor in Washington University's Department of Immunology who led the study.

Pepper and colleagues published their findings in the journal Cell

Immunity to SARS-CoV-2 can be acquired in two ways: infection or vaccination

In the new study, the researchers tried to find out why

They found that after vaccination, those who had been previously infected developed more memory B cells, which produced antibodies that neutralize the virus and prevent infection

"Even if their first infection was caused by the earliest Wuhan strain and their vaccine was based on that strain, people with hybrid immunity are able to produce neutralizing antibodies against what we gave them," Pepper said.

Mixed immunity also generates a cellular immune response, more specifically against viral infection, called the Th1 response

"While additional vaccination increased the number of CD4+ T cells in the uninfected population to levels seen in the infected population, it failed to generate the same quality of CD4+ T cell responses as the mixed immune population," Pepper said

Several factors could explain why mixed immunity appears stronger

In the case of the mixed immunization group, one year from the time of infection until they received the vaccine

Another factor may be where the immune system first interacts with invading pathogens

Exposure to lung and mucosal tissues, such as cells in the nasal passages, may result in better immune responses to respiratory pathogens because the cells are better retained at those sites, Pepper said

Pepper said that while vaccination following a previous infection appeared to generate an enhanced immune response to SARS-CoV-2 infection, it was crucial that people who were already infected were vaccinated to reap this benefit

article title

Imprinted SARS-CoV-2-specific memory lymphocytes define mixed immunity