Earlier this year, the Centers for Disease Control and Prevention announced its annual flu vaccine was only 23 percent effective. For many people, news of this efficacy rate meant the recommended inoculation was simply not worth the bother. Now, a team of researchers may add fuel to the apathy fire with their suggestion that, once you hit 30, you most likely will come down with the flu only twice a decade anyway.

Many people would never describe themselves as “anti-vaxxers,” yet in practice they demonstrate a few of those tendencies; they avoid getting the government-recommended yearly flu shot and look away whenever someone asks them whether their teen-aged son has gotten his shots for Gardasil, the HPV vaccine. (“Does he really need it,” they mutter before changing the subject.) Some parents, due to confusion or a desire to “space out” the pain for their young children, will delay shots and create their own vaccination schedule, though no one in the health care business would ever recommend this.

Our true opinions are best expressed by our actions, which fall somewhere along a continuum between two extremes, with anti-vaxxers on the one end and pro-vaccination types at the other end. Naturally, most of us are moderates. We avoid the hot light of controversy and get away with whatever we can. Hey, there’s freedom in the middle.

Building Immunity Naturally

For the current study, a team of researchers from Imperial College London and Johns Hopkins University analyzed blood samples from volunteers in Southern China. They looked at antibody levels against nine different influenza strains that circulated in the region between the years 1968 and 2009. Next they calculated the effects of each person's individual medical history, since every bout of the flu confers some natural immunity against future viruses.

“What we've done in this study is to analyze how a person's immunity builds up over a lifetime of flu infections,” said Dr. Adam Kucharski, of London School of Hygiene and Tropical Medicine.

What did Kucharski and his colleagues discover? Kids, on average, became infected every other year, while adults got the flu less frequently over time. In fact, from age 30 onwards, the participants in the study came down with the chills and fevers of the flu at a steady rate of about just two times per decade.

“For adults, we found that influenza infection is actually much less common than some people think,” said Dr. Steven Riley, senior author and a professor at Imperial College London.

But hey, you decide whether this will influence your thoughts about an annual flu shot.

Source: Kucharski AJ, Lessler J, Read JM, et al. Estimating the Life Course of Influenza A(H3N2) Antibody Responses from Cross-Sectional Data. PLoS Biol. 2015.