A person's ability to fight off influenza is determined by the subtypes of flu they've had in the past, according to a study published in journal PLoS Pathogens.
For the study, researchers from the University of California Los Angeles and University of Arizona in Tucson examined health records from the Arizona Department of Health Services.
They found two flu virus subtypes, H3N2 and H1N1, have been responsible for the seasonal outbreaks of the flu over the last several decades. The data also showed that those who were first exposed to H1N1 — the less severe strain of the two — during their childhoods were less likely to hospitalized if they were exposed to H1N1 again later in life, compared to people who were first exposed to H3N2.
Similarly, those exposed first to H3N2 during their childhoods gained extra protection against H3N2 later in life, than those who were first exposed to H1N1.
"The second subtype you're exposed to is not able to create an immune response that is as protective and durable as the first," said Michael Worobey, PhD, a co-author of the study and head of the University of Arizona's department of ecology and evolutionary biology.