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Ready for a little mosquito bite?



That’s what my pediatrician used to say when he was about to give me a shot. Although shots were much scarier when I was 6, I wouldn’t exactly say I’ve grown into them. That’s why when flu season comes around I’m not the first in line to get vaccinated. I’ve gotten plenty of flu shots in my life, but in recent years I have not taken the vaccine as seriously as some perhaps do. However, considering the way vaccines work I should probably rethink my logic.

Before we can think about vaccines though, we should probably think about viruses themselves. A virus is sort of pitiful because it can’t multiply on its own. Unlike our cells which can grow and divide happily, the virus needs a host cell to help it multiply. Instead of asking politely, the virus sneaks some of its genetic material into our healthy cells and our cells unknowingly regenerate this genetic material into more viruses!  Luckily, this is when our immune system kicks in.

Our immune system is a slurry of specialized cells whose main job is to search and destroy foreign entities like viruses. However, these specialized cells need some way of figuring out which entities are viruses and which are healthy cells. Imagine you are blindfolded and told that one of your good friends is about to greet you. You can’t see them so you must depend on other clues, like the way their hand feels when you shake it or how tall they are when you hug them. This is sort of how your immune system recognizes the viruses it is working so hard to destroy.

Just like your friend has a distinctive shape, viruses have molecules protruding from their bodies that have distinctive shapes. Our immune cells “shake hands” with all the entities they come into contact with and distinguish the viruses from healthy cells by the shape of those protruding molecular hands. But if our bodies are so good at detecting and destroying viruses why do we use vaccines?

Vaccines give our bodies a leg up in the search and destroy part of the immune response. The first time a virus enters our body it will take a while for our immune cells to recognize the threat because they have never encountered the virus’ molecular shape before. However, our immune systems are good at remembering what molecular shapes they have encountered in the past, and when they meet again the virus doesn’t stand a chance.

You’ve probably heard that vaccines contain a little bit of virus in them, which sounds terrifying! The doctors are injecting you with the flu! This is true to an extent, but the shot only contains bits and pieces of the virus. Crucially, it only contains the bits and pieces that allow your immune system to meet the virus and “shake hands” with it without any real danger of a full blown infection. This way if some of the active virus does get into your body from your friend’s sneeze or your neighbor’s cough, your immune system will recognize it immediately and kill it before it kills you.

There is a lot more to learn about viruses and vaccines. Why do we need a new flu vaccine every year if we only need one measles vaccine in our lifetime? What are the virus’ “molecular hands” actually made of? Answer to those questions and more can be found in the sources and further reading, and all over the internet!

Sources and further reading
“Influenza, an ever-evolving target for vaccine development." Understanding Evolution. University of California Museum of Paleontology. 1 October 2013. http://evolution.berkeley.edu/evolibrary/news/130201_flu

Saranya Sridhar, et al. (2013) Cellular immune correlates of protection against symptomatic pandemic influenza. Nature Medicine, published ahead of print 22 Sept 2013.

Zambon, M.C. (2001) The Pathogenesis of influenza in humans. Rev. Med. Virol. (4) pp 227-241.

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