How to lose friends by influenza-ing people

1918 Influenza Poster:The History of Medicine: image is in the public domain

The 1918 flu outbreak killed 50 million people. 1918 Influenza Poster:The History of Medicine: image is in the public domain

Ah, it’s the end of autumn, a lovely season. The air has turned cool and crisp, leaves are red and gold – and everyone beside you at the bus stop is sneezing and coughing. Influenza season is officially here! Are you ready? Have you had your flu vaccine? – well, you probably should.* No, it can’t give you the flu. And no, it doesn’t matter that you got one last year. Let me explain.

First of all, know your enemy. There’s a big difference between Big Bad Influenza** and the sniffles and stomach viruses that often get mislabelled as “flu”. Influenza is a potentially serious respiratory disease that starts out as a cough and sore throat. It then progresses to a fever with severe aches and chills. There’s a miserable week in store for anyone unfortunate enough to have been blindsided by someone’s sneeze. In some high-risk cases, influenza can kill. Luckily for us, influenza is one of several vaccine-preventable diseases. That means we have the power to stop flu from ever making us sick, as long as we can prepare the immune system in time.

That’s what vaccines do – they introduce a little fragment of a bad-guy virus or a bacterium to your immune system, which fights it as though it were a real enemy. Your white cells then leave wanted posters around your body, so if the same intruder ever tries to get back in it’ll be spotted and taken out immediately, before it can do any damage.

The cough, sore throat and misery associated with flu are caused by a virus that is partial to the human respiratory tract. The virus is a small core of genetic material called ribonucleic acid (RNA) which is wrapped in a protective envelope of glycoproteins (sugar molecules stuck onto proteins). Its infection strategy hinges on two particular glycoproteins, scattered across its envelope like sesame seeds on a bagel. These are haemagglutinin (H), which allows the viruses to enter the host cells so they can replicate, and neuraminidase (N), which busts the fresh army of viruses back out to infect other neighbouring cells. Those two glycoproteins are extremely variable, which means the genes that encode them are prone to mutations that alter the final product.

That variability is a major reason that underlies why making the flu vaccine is so tricky. Most of the other vaccines you’re familiar with – like measles and tetanus – target viruses or bacteria with a rather stable set of antigens. Once your immune system has gone through its training program (via vaccination or actual infection), it can’t miss the intruder if it comes back. But the influenza virus drifts around so much that a single vaccine can’t possibly cover all of the possibilities. It’s like the virus is Mr Potato Head, and every time it changes out its nose for a new look our immune system thinks it’s somebody new. Influenza is particularly drifty because the enzyme (RNA polymerase) that copies influenza’s genetic material is terrible at its job and doesn’t have a proofreading mechanism. This introduces tons of mutations and is essentially the reason why we need a new vaccine every year – within a short period the virus has mutated to an entirely new threat.

So how do we choose what to put in the vaccine? It’s not easy, and we don’t always get it right. Careful monitoring of flu cases in Asia can usually give us an idea about which variant is virulent enough to spread quickly and cause serious disease. That’s because Asia is a vast expanse of the world where many people still live in rural settings in close quarters with livestock – which matters because influenza can also infect animals. Birds and pigs are particularly susceptible to influenza, which is where the names “bird flu” and “swine flu” come from. When two viruses meet up in one body – whether it’s a chicken, a piglet, or you – they can get intimate with each other and spread new mutations. This unfortunately means that anywhere you have a large population of people, birds and pigs living close together is a perfect spot for new virus variations to sprout up: therefore this is why so many influenza epidemics get their start in countries such as China.

Colorized transmission electron micrograph of negatively stained SW31 (swine strain) influenza virus particles. Credit: NIAID Image licensed under CC BY 2.0

Colorized transmission electron micrograph of negatively stained SW31 (swine strain) influenza virus particles. Credit: NIAID
Image licensed under CC BY 2.0

Once the world’s expert epidemiologists make their guess at which variant(s) will be the most virulent and cause the biggest problems worldwide, the vaccine manufacturers use that information to make the next year’s batch of vaccine. There are a few ways to make the vaccine, but the most common method right now is to grow them in eggs: more specifically, fertilized chicken eggs. Because the influenza virus grows well in chickens, we’re able to inject virus into eggs, incubate these for a few days, and then harvest a few millilitres of liquid from each egg. That liquid is chock-full of viruses, which are then treated with chemical processes to make them inert and incapable of infection. The basics are all still there for the immune system to recognize, but they can’t get into host cells and replicate – so they can’t make you sick.

Many people hesitate to ask for the flu vaccine because they worry it’ll make them ill. Unfortunately, humans have a gift for imagining correlations where there may well be none, and so any illness caught around the same time as the vaccine might make some think they “caught flu” from that needle in their arm. Given that flu vaccination season comes right alongside sniffle season, it’s easy to see how so many people end up sick near their flu jabs. But the viruses in the vaccine are dead, – unless you are given the nasal mist, which contains has weakened viruses – this is specifically withheld from the very young or very old for that reason. A dead virus cannot infect you with influenza, so don’t blame your nurse!

The thing the flu vaccine can do, though, is make your arm sore for a day or two (you’ve been stabbed, give yourself permission to have a sore arm). It also triggers an immune response, and in some people that can mean a headache or body aches for a day or two.

The other thing the vaccine can do? Protect you from influenza, which is a nasty nasty illness even if you’re normally as strong as an ox.

So unless your doctor has said you have medical reasons to stay away from vaccines, or you’ve got an egg allergy – in which case alternative vaccines might be available if you ask – you should be in line with your sleeve rolled up for your vaccine. Not only are you protecting yourself, but you’re protecting everyone else who can’t get the vaccine. Join us in the herd!


JenJen MacCormack is a self-described “mad laboratorian” currently working on transforming human plasma into blood typing antisera. She’s approximately 40% coffee by volume and expends excess energy on her growing portfolio of science writing.

* Check your local doctor’s policy on offering the flu vaccine – in the UK, it is typically offered to people considered to be at a higher risk of complications, such as pregnant women, older people and those with heart conditions. However if you don’t belong to the above categories but work in a school or hospital you may also be eligible.

** The 1918 flu outbreak killed more people than the First World War.

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