While children typically get flu once in two years, adults who are at least 30 years old catch flu only about twice in a decade, suggesting that adults who felt sick and blamed it on flu could be wrong.
For the new study, which was published in the journal PLOS Biology on Mar. 3, Steven Riley from the Imperial College London in the United Kingdom and colleagues examined the blood samples of 151 individuals from Southern China, testing each of these against nine strains of influenza A, or H3N2, virus that circulated between 1968 and 2009.
By looking at the presence of antibodies in the participants' blood, the researchers were able to determine whether a volunteer had been infected with flu and how often. The body's immune system responds to flu virus with the production of antibodies that target proteins on the surface of the virus. These proteins may change with the evolution of the virus, but the antibodies in the blood have a signature for strains that an individual has encountered before.
They found that while children get flu every other year on average, flu infection appears to become less frequent with age. In individuals who are at least 30 years old, flu infection was likely to occur about twice per decade, showing that influenza infection is much less common than what some people think. The frequency of infection, however, depends on vaccination and background levels of flu.
The researchers were likewise able to come up with a mathematical model of how immunity against the disease can change over lifetime as people encounter different strains of the virus, strengthening results of other earlier studies showing that the flu virus strains that people encounter earlier in life produce stronger immune responses compared with those that infect them later.
Findings of the new study are crucial as these could help scientists predict how the flu virus will evolve in the future. The results also show how immunity to the historical strains will have an impact on how vaccines work and how effective they will be in providing protection against the illness.
"These results demonstrate the value of interpreting immune responses in the context of a lifetime of infection," the researchers wrote. "Integrating the life course of immunity into future analyses of influenza dynamics could therefore lead to a better understanding of population susceptibility and the potential transmissibility of new seasonal strains."
Photo: Tara Hunt | Flickr
