Flu Infections Level Off As Adults Age

New findings published in PLOS Biology show that adults over the age of 30 may only catch the flu about twice a decade. The study results are based on the analysis of blood samples from volunteers in Southern China, while researchers examined antibody levels against nine different influenza strains that circulated from 1968 to 2009.

Children get the flu a lot more often than adults do, at once every other year. However, from the age of 30 onwards, flu infections tend to level off at a steady rate of every two decades or so.

"There's a lot of debate in the field as to how often people get flu, as opposed to flu-like illness caused by something else. These symptoms could sometimes be caused by common cold viruses, such as rhinovirus or coronavirus," said Dr. Adam Kucharski, who worked on the study at Imperial College London before moving to the London School of Hygiene & Tropical Medicine, in a news release. "Also, some people might not realise they had flu, but the infection will show up when a blood sample is subsequently tested. This is the first time anyone has reconstructed a group's history of infection from modern-day blood samples."

Researchers from the UK, the US and China also developed a mathematical model of how to determine how our immunity to flu changes over a lifetime as we encounter different strains of the virus, in addition to estimating the frequency of flu infection.

The immune system responds to flu viruses by producing antibodies that specifically target proteins on the virus surface. These proteins can change as the virus evolves, but we keep antibodies in the blood that have a memory for strains we've encountered before.

The research supported evidence from previous studies, showing that strains of the virus develop stronger immune responses that we meet later as we age.

"What we've done in this study is to analyse how a person's immunity builds up over a lifetime of flu infections," Dr. Kucharski concluded. "This information helps us understand the susceptibility of the population as a whole and how easy it is for new seasonal strains to spread through the population."

For more great science stories and general news, please visit our sister site, Headlines and Global News (HNGN).