The discovery comes via research conducted by Penn Medicine, which completed studies of blood work taken from 140 children (aged 1 to 17) and 212 adults (aged 18 to 90). The results, published in the journal Nature Communications, showed that middle-aged people born 40 to 50 years ago had specific antibodies present in their system that were able to bind to the H3N2 viruses that cause the flu, but not prevent full infection from occurring—putting anyone in that age group at a higher risk of developing the flu.ae0fcc31ae342fd3a1346ebb1f342fcb The study also found that children between the ages of 3 and 10 had high levels of “neutralizing antibodies” in their system, making the younger generation better able to stave off the disease. Since childhood exposure to the H3N2 viruses by the age of 4 is responsible for establishing lifelong immune system responses, researchers concluded that a change in the prevalent strain of the virus over time has made certain adults less capable of fighting off the yearly bug. “We found that different aged individuals have different H3N2 flu virus antibody specificities,” lead author Scott Hensley, PhD, an associate professor of Microbiology at the Perelman School of Medicine at the University of Pennsylvania, said in a statement. “Our studies show that early childhood infections can leave lifelong immunological imprints that affect how individuals respond to antigenically distinct viral strains later in life.” RELATED: For more up-to-date information, sign up for our daily newsletter. The study upholds a previous theory that a lack of specific antibodies in middle-aged adults can put them at a higher risk of getting the flu. According to the CDC, the 2013-2014 flu season saw an unusually high number of middle-aged patients struck down by the virus. A recurrence of the phenomenon during the 2017-2018 season was also referenced by the study’s researchers. However, while susceptibility may increase for some Gen Xers, the CDC points out that the risk of hospitalization and death from a severe case of the flu typically increases once you hit the age of 65. And for more on how age may be more than just a number, check out COVID Is 14 Times Deadlier If You’re Over This Age, Research Shows.