What Your Birth Year Might Say About Your Flu Risk

A new study's findings go against what experts have believed for decades.

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When it comes to the flu, no news is usually the best news. But we've got some potentially good flu news for you: Just for enduring your very first bout of the flu when you were a kid, you might have a significantly reduced risk of infection by similar, more severe flu viruses — but which one depends on the year you were born.

In a November 2016 study, researchers from the University of Arizona and the University of California, Los Angeles, found a connection between the year of someone's birth and their risk of serious infection or even death by certain types of influenza A (aka avian or bird flu) viruses. This is major, because up until this point experts had always thought that you couldn't develop immunity to influenza A viruses.

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The researchers looked at the medical data of every known patient who had either become seriously ill or died as a result of two types of influenza A — the H5N1 virus and the H7N9 virus — both of which are known for causing severe illness or death when they spread from birds to humans. A pattern emerged: People born prior to 1968 were less likely to get seriously infected with the H5N1 virus, and people born after 1968 were less likely to get seriously infected with H7N9 virus.

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Influenza A viruses can be separated into two different groups based on the type of hemagglutinins, aka receptor proteins, they carry: "Group 1" is made up of the H1, H2, and H5 viruses, and "Group 2" includes the H3 and H7 viruses. The researchers found that people who were less likely to get H5N1 (aka born before 1968) were most often exposed to H1 and H2 viruses in their youth, while people who were less likely to get H7N9 (aka born after 1968) were most often exposed to H3 viruses. This suggests that if your very first flu was a Group 1 virus, that virus might have made an "imprint" on your immune system, which in turn might reduce your risk of being infected by another type of Group 1 virus later on in life.

Of course, there are some limitations to this research. For starters, it's more difficult to determine which type of virus first infected a person born in the 1970s or later and how that affected his or her immune system, because at that point both Group 1 and Group 2 viruses existed and were infecting humans. Researchers also aren't sure just how well this "imprint" protects a person from other similar flu viruses: Could it mean he or she is completely immune and will never even get infected by that group of viruses again? Or could they could still get infected by the virus but just not get as sick? Clearly, more research is needed.

But in the end, this is a huge step forward in our knowledge of influenza A viruses, and with further research, scientists might be able to use this info to improve vaccines. But until then, it's definitely your best bet to continue to get the flu vaccine each year.

[h/t CNN]

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