While the dangers of the flu may make headlines every flu season, researchers have calculated that adults over the age of 30 only catch the flu about once every five years.
While children catch the flu more often than not, usually averaging every other year, influenza infections become less frequent as people mature through childhood and early adulthood. From the age of 30 onwards, flu infections tend to occur at a steady rate of two per decade.
"For adults, we found that influenza infection is actually much less common than some people think," senior author of the study, Steven Riley from at Imperial College London says. "In childhood and adolescence, it is much more common, possibly because we mix more with other people."
For the study published in the journal PLOS Biology, researchers analyzed blood samples from volunteers in China, examining antibody levels against different strains of influenza that circulated between 1968 and 2009.
"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," said Adam Kucharski, who worked on the study at Imperial College London before moving to the London School of Hygiene & Tropical Medicine.
"These symptoms could sometimes be caused by common cold viruses, such as rhinovirus or coronavirus. Also, some people might not realize they had flu, but the infection will show up when a blood sample is subsequently tested."
Other viruses and illnesses can show flu-like symptoms, making it difficult to assess how often people are actually infected with influenza.
In addition to estimating the frequency of flu infection, researchers also developed a mathematical model of how immunity to flu changes over a lifetime as we encounter different strains of the virus. The model supported evidence from other studies that the strains of influenza we encounter earlier in life evoke stronger immune responses compared to those we meet later.
Despite these new statistics, that doesn't mean you shouldn't get a flu shot each year. The flu shot is one of the best ways to protect yourself from the flu and considering the seriousness of some of the strains of influenza, the shot could mean the difference between life and death. However, this new data demonstrates that it is often not as infectious as we once thought and, in many cases, our bodies are easily able to fight off the virus depending on the strain of influenza we encounter.
