A patient’s antibody response to the influenza virus is drastically shaped by preexisting immunity, according to a study published in Science Translational Medicine.

The flu vaccine woks by exposing the immune system to a small amount of the influenza virus, which causes B cells in the body to develop a biological memory. If the body encounters the same virus at a later date, the immune system is alerted to attack and eliminate the virus. However, new research suggests that vaccinations can draw upon preexisting immunity. 

The study found that most of the initial antibodies that are stimulated after flu infections and vaccinations come from old B cells. This indicates that cellular memory plays a big role in how the body reacts to early viral infection. Additionally, investigators found that there was a higher level of activity toward flu strains that circulated during childhood rather than more recent strains. 

The study highlights the importance of the seasonal flu vaccine, according to the authors. The structural parts of the influenza virus that do not change are better for antibodies to target than the parts that don’t. Investigators believe that a person’s age, exposure to influenza, and the type of exposure all factor into whether the immune system targets neutralizing or non-neutralizing sites on the virus. 

"For people who have caught the flu, their pre-existing immunity may make them susceptible to infection or increase the severity of their influenza symptoms if their antibodies are targeting 'bad' or non-neutralizing viral sites," said co-first author Jenna Guthmiller, PhD, in a press release.

The study authors said this research also plays an important role in the development of a universal flu vaccine. According to the study, a universal influenza vaccine must focus on the parts of the virus that do not mutate over time and antibodies that can effectively target them. 

REFERENCE:
Pre-existing flu immunity impacts antibody quality following infection and vaccination [News Release] December 11, 2020; Chicago, Ill. Accessed December 15, 2020. https://www.eurekalert.org/pub_releases/2020-12/uocm-pfi121120.php