Science, Pseudoscience, & Media Literacy

Will the Influenza Vaccine Make You Sick?

nurse administering intramuscular injection

I’m trotting out a reworked version of a post I did last fall because flu session is coming, and it’s time to decide whether or not to get the influenza vaccine.

There are a lot of myths floating around the influenza vaccine, and it’s always better to make choices related to your health that are based on facts rather than myths.  One of the common myths is that the vaccine will give you the flu, so that’s the focus of this post.

Vaccine basics

When an infectious agent enters the body, its goal is to start replicating and making more of itself.  Your immune system wants to shut that down.  There are several layers to the immune response, and a key element is the production of antibodies.  These are Y-shaped proteins your body makes that are specific to that infectious agent.  They latch onto it and sort of wrestle it to the ground so that other components of the immune system can go to town.

The body is good at remembering antibodies it has already made.  The next time it’s exposed to the exact same infectious agent, antibodies can be produced quickly so they can take care of the infectious agent before it makes you sick.

Vaccines expose you to a part of the infectious agent so your body can produce antibodies before you’re exposed to the infectious agent itself.  There are two broad groups of vaccines: one is live attenuated (weakened virus that is still capable of replicating) and the other is inactivated (the virus is unable to replicate).

The influenza vaccine

The diagram above shows an influenza virus.  The squiggly bits in the middle are the viral DNA, which is what gets you sick.  That’s contained within a capsule, which has various proteins sticking out of it (the purple and gold coloured bits).

The injectable flu vaccine contains proteins that are found on the outside of a flu virus, specifically forms of hemagglutinin (H) and neuraminidase (N).  There’s no viral DNA contained in the vaccine, and the DNA is what makes you sick, so the injectable flu vaccine can’t possibly give you the flu.  There’s simply no biological mechanism for this to happen.

The nasal spray formulation of the flu vaccine is different.  It contains live weakened virus.  It’s not going to make people with a healthy immune system sick, but people who are immunocompromised or on immunosuppressant medications can get sick, so it’s generally recommended that they avoid live vaccines.

What’s good and what’s not about the influenza vaccine

Let’s start with the bad.  Influenza is not a stable virus.  It mutates a lot, and the predominant strains change from year to year.  You may recall hearing about the H1N1  flu or other letter/number combinations.  The H and the N correspond to the hemagglutinin and the neuraminidase protein that the flu virus attacks.  The numbers refer to different variants of these proteins.  The World Health Organization predicts the most common strains for the upcoming flu season, and vaccines are developed to target those H and N types.

The problem is, the flu virus doesn’t necessarily do what the WHO predicts it’s going to do.  As a result, you may not end up covered for all the flu strains you might be exposed to in a given year.  This means the flu vaccine is a lot less effective overall than other vaccines for more stable infectious agents, and you may end up getting sick with the flu from a strain of the virus that’s not covered by the vaccine.

Now it’s time for the good.  Those immunocompromised people who shouldn’t take the live virus nasal spray vaccine?  If they catch the flu, it could actually kill them.  Same with the elderly.  People with chronic respiratory conditions can also have significant complications from the flu.  These are the people that need protecting, and that’s why getting vaccinated is important.

If you catch the flu, you’re already infectious the day before you start to feel sick.  Say you’re going to visit your grandparent in a care home.  You unwittingly spread your germs all over the place.  People get seriously sick.  Not good, right?

As a nurse, I’m required to get a flu shot, not for my own protection, but for the protection of my patients that I could pass my germs to.

If you’re not coming into contact with people who are at high risk of complications from the flu, it’s probably not that important to get the vaccine.  Then again, the more people who get vaccinated the safer it’s likely to be for at-risk people.  You can find out more about this concept in a post I did on herd immunity.

What if you get sick after the vaccine?

One option is that when your body is generating the immune response that it’s supposed to, you may feel a little under the weather.  This isn’t an infection, it’s your body doing its thing.

Another option is that you were exposed to a strain of flu virus that wasn’t covered by the vaccine, and the timing just happened to coincide with when you got the flu vaccine.

It’s also possible that you got a cold.  While colds and the flu are both respiratory infections, they are completely different viruses.  That means the flu vaccine gives you zero coverage for colds.  The flu causes achiness all over, extremely low energy, and a significant fever.  If you don’t have a fever, chances are you’ve got yourself a cold.

On a related note, the term “stomach flu” is a misnomer.  Influenza is a respiratory virus that doesn’t affect the gut.  “Stomach flu” can be caused by a variety of infectious viral or bacterial agents, none of which are influenza.

Well, there you have it.  It’s up to you whether you get the flu vaccine or not, but informed choices are always better than choices based on myths.

In 2020, the time of COVID, it’s actually even more important to get the flu vaccine. Read why here.

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37 thoughts on “Will the Influenza Vaccine Make You Sick?”

  1. I’ve been getting a flu shot every year since 1991, when I got the flu and was so sick. The one year I didn’t bother (2014)? Flu! Ughhh. I know I might get a strain that’s not perfectly covered by the shot, but so far so good!

  2. Great topic! Both me and my husband caught the flu recently and it was the worst! Myalgia, fever, chills, vomiting, headache! we were lucky we took oseltamivir very early ! And there’s another new treatment (baloxavir) which is only one dose.
    The vaccine recommendations keep changing regarding the doses, but as you have mentioned people have a lot of misconceptions! your post really clarify these misbelieves in a simplified way! thanks for sharing this !

  3. Very well covered, Ashley. I’ve always been reasonably encouraging towards the ‘get the flu jab’ way of thinking and must admit I thought the experiences of people getting the flu after the jab were just a coincidence. Then it happened to me, and my experience has been a little off-putting.. I know in theory it can’t give you the flu and that there’s no live virus. My mother very, very rarely gets sick. She hasn’t had a flu in years, I don’t think I can even remember her having it. Colds, yes. Flu? Not so much. She had her first flu jab two years ago and about 3 days later she came down with the flu and she was so incredibly poorly – she even went to bed in the day (that never happens!). She won’t have it again. Last year I had the flu jab for my second time – the first time was fine, but this time three days later I came down with the flu quite badly and I’ve never felt that poorly from the flu before. Got it again a month later, too! So I don’t know, it’s just a bit off-putting. I haven’t decided whether to get it this year or not now. xx

  4. Mixed experiences with the flu shot. I reacted poorly once and regretted it. I’m inconsistent over the past several years. Think I may get it this year because the flu never seems to leave me. Terrific post and timely.

  5. I have a question, maybe it’s a silly one I don’t know. Can it be that when many people get the vaccinatiion, the virus in it turn mutates more quickly? So the mutated form affects more people in the end?
    I myself never got the shot because I think it’s natural for the body to get ill. I never got the flu though while working.
    I think it was a very secret wish to have a rest. A very selfish one I can see now and I’m not proud of it. I would rather be ill in bed than dealing with the mental stuff. But that is a very different topic.

    1. Rest is nice… I doubt I’d get the flu shot if it wasn’t for work. For my own sake getting the flu would be unpleasant but not be that big a deal.

      I haven’t heard of vaccines promoting the way overuse of antibiotics can promote the propagation of antibiotic-resistant bacterial strains. High rates of vaccine use provide “herd immunity” because with so few people susceptible it’s hard for the bacteria or virus to spread. And smallpox was eradicated by high rates of vaccine use.

    2. I actually did just read an article somewhere that said the flu shot was found in some study to be less effective when you got it every year! But I still get it- it’s that or wear a mask at work, and I don’t want to do that. Plus, just in case…the flu sucks so bad.

  6. I hadn’t had the flu shot for 10 years til last year. It wasn’t on purpose, I just never thought about it. The first night I got the side effects which are similar to the flu but I was fine by morning. But I haven’t been sick all year except a few colds.

  7. You’ve inspired me to look into it already. I’ve been on the fence due to the whole ambiguity of it all, but I need to figure out what it’ll cost me and if going to Prague would increase or decrease my need. There’s a really nice little clinic at my grocery store, and I need to stop by and ask them!! Thanks for all this info!!

  8. I’ve had my flu jab not long ago andveach year I have it.
    I don’t know how many years I have accepted them. My asthma has been longer than the injections.

      1. I would recommend the flu jab if you are in the criteria for it.

        Mum did not have her flu jab last year, so that’s why she ended up in hospital with it, back in February.

          1. All depends on if mum has her flu injection.
            Mum is prone to chest infections, so she should really have it. It’s all because of the myths around it, giving you flu, etc

            1. I imagine with her being on the mental health unit ward and being quite a few vulnerable people on there, that someone comes on the ward to offer the flu injection. But not sure on this. With her not being in a position to go home yet.

  9. Thank you for ALL of this. As a person who works in healthcare, I cannot count the number of times I’ve heard “The flu shot gave me the flu” or “I have the stomach flu” & I have explained it until I’m blue in the damn face. The government isn’t trying to pull anything over on you. You aren’t allergic to the flu shot. Please gtfo of here with your nonsense. The worst thing you got was a sore arm and your “stomach flu” is another bug entirely. Just…stop. Hahahaha!

  10. I’ve taken the flu shot, because well last year I got SO sick for like a month and it really impacted my job (it didn’t help either that I worked with preschoolers either). So since last year I started taking the flu shot and helps me to avoid the flu or go through it without the harsh effects of the flu (seems ever since my anxiety has worsened, my immune system has taken a dive). The trick is to take one tablet of ibuprofen or Tylenol AFTER taking the flu shot.
    Though this year was different cuz I did undergo some flu like symptoms, but I don’t know if it’s because I got my shot from another clinic compared to the place I got from last time or the fact I’ve been working two jobs🤔😕

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