😰WHY DOES FLU KEEP
COMING BACK 🤕
☁️☁️☁️☁️☁️🌦🌦🌦🌦🌦🌦
🖍Flu is unique among human diseases.
🖍It circulates constantly in cool, dry areas of east Asia, conditions the virus prefers,
but when temperatures drop during the northern and southern winters, it breaks
out and begins a tour of the relevant hemisphere.
🖍Flu spreads from person to person efficiently in exhaled droplets, and can be picked up from contaminated surfaces, nearly everyone is exposed.
🖍And unlike, say, measles, having flu once doesn’t make you immune to catching it.
🖍 The virus is uniquely talented at dodging our immunesystems.
🔘🔘 The big haemagglutinin protein on its surface gets most of your immune system’s attention, and this protein constantly mutates at seven hotspots.
🖍Every few years it racks up such a number of mutations
that many antibodies you made to your last infection don’t recognise the virus, and you get sick again.
🖍You still have some immunity to kinds of flu that are only a little different from viruses you have seen before, which is why
much winter flu isn’t as severe as flu can be.
🖍The strains best able to evade this kind of prior immunity dominate the annual epidemic in each hemisphere, so we only need one vaccine per season but a new one each year.
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