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Home » Flu vaccine facts – countering those anti-vaxxer myths and tropes

Flu vaccine facts – countering those anti-vaxxer myths and tropes

It’s that time of year again, where we urge you to get the flu vaccination. And it’s time to provide you with the flu vaccine facts to debunk the anti-vaxxer fear, uncertainty, and doubt. Or we can just call them lies.

This article is not going to focus on every pseudoscientific anti-vaccine claim about the flu vaccine. It would take 10,000 words, and none of you, no matter how loyal you are to this old dinosaur, is going to read that many words. The goal of this post is to present flu vaccine facts for the biggest myths we read every year about the vaccine.

So, here we go.

Flu vaccine facts – producing the vaccine

Without getting too complicated, the flu vaccine induces a systemic immune response to a part of the influenza virus called hemagglutinin, which is a glycoprotein found on the surface of influenza viruses. Both inactivated and live, attenuated influenza vaccines induce virus-specific serum antibodies which should attack wild influenza virus possessing the same hemagglutinin antigen.

The reason that each flu season brings a new risk for contracting the disease is that the virus has frequent mutations of this hemagglutinin antigen, so the immune system doesn’t recognize the virus anymore, and you contract the flu. It doesn’t matter if you get the flu “naturally” or boost your immune system with a vaccine, you are generally susceptible to a newly mutated flu virus each year.

Of course, this makes it difficult to develop a flu vaccine every year, because national health organizations, like the US Centers for Disease Control and Prevention, have to scientifically predict which mutated viruses might be prevalent in the upcoming flu season. 

Moreover, vaccine manufacturers require a six-month lead time from choosing the virus to shipping the vaccine. This requires vaccine scientists to quickly determine what the new mutated types might be and pass the information to the manufacturers.

The first step in this process includes participation from over 100 national influenza centers in 100 countries who receive and test virus samples from patients in their countries. These centers then send samples of the most prevalent viruses to five World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza. Those collaborating centers are:

Twice a year, February for the Northern Hemisphere and September for the Southern Hemisphere, WHO gathers the five Collaborating Centers to meet and discuss which flu virus strains are going to be prevalent in those areas (see Note 1). 

The key scientists from each of these centers review the results of surveillance, laboratory, and clinical studies, and the availability of vaccine viruses and make recommendations on the composition of the upcoming season’s influenza vaccine. Generally, the group decides on three subtypes of the flu virus – H1N1 (a subtype of A flu), H3N2 (another subtype of A flu), and type B strains. Recently, a second subtype of the B type virus is included in the quadrivalent flu vaccines.

WHO recommends specific vaccine viruses for inclusion in influenza vaccines; however, each country reviews the data and may modify the viruses in the vaccines for their own country. For example, in the USA, the Food and Drug Administration (FDA) makes the final decision about vaccine viruses, with input from the CDC, that will be used in vaccines sold in the USA.

No, this decision process is not guesswork, it actually is a fairly complex scientific process to ascertain which strains of influenza A or B might circulate in the Northern and Southern hemispheres. As opposed to some of the beliefs out there, this isn’t random guessing, like throwing darts at influenza strains and say, “we’re including that one.” In fact, it is a logical, scientific process that includes some of the leading experts on the flu virus from across the world. Although the process is far from perfect, for example, it’s difficult to predict a new mutation that appears after the February or September meetings, it works well enough in most years.

The 2018-2019 flu vaccines will include the following strains:

  • A/Brisbane/02/2018 (H1N1)pdm09-like virus
  • A/Kansas/14/2017 (H3N2)-like virus
  • B/Colorado/06/2017-like virus (Victoria lineage)
  • Quadrivalent vaccines also include the B/Phuket/3073/2013-like virus (Yamagata lineage)
A baseball photo to go along with my baseball metaphor. Photo by Joshua Peacock on Unsplash.

Flu vaccine facts – flu vaccine effectiveness

In the 2018-19 flu season for the Northern Hemisphere, the CDC estimated that the overall effectiveness of the flu vaccine was around 29%. Although the effectiveness was around 49% for young children, it is clear that it is far from perfect. However, given the significant complications and costs of a flu infection, even reducing the risk by half has an important benefit to humans. Furthermore, given the very low risks from getting the shot, the benefit to cost equation is overwhelmingly on the side of benefit.

One of the odd anti-vaccine beliefs about vaccine effectiveness is that the effectiveness is “no better than random.” Math, it’s not that hard. 

Yes, if you flip a coin, which is completely random, you would expect that heads or tails would appear 50% of the time. Any deviation from that probably means there’s some extenuating non-random factor influencing the outcome.

Vaccines and flu infections are most certainly not random, outside of some chance variables like standing in a store next to some guy hacking out his mucous for you to inhale, just before getting the flu vaccine. 

Think of it this way – a good baseball player gets a hit about 30% of the time (hey, Keith Law, I’m using a baseball metaphor for a vaccine, that should be worthy of a mention on Baseball Tonight podcast). A really good player does it about 35%. If we thought baseball was totally random, then any player would get a hit 50% of the time based on some cosmic coin toss.

Now, there is some randomness to the game. A ball can be hit, and a fielder gets a late start and can’t catch the ball. Or a ball is hit and a breeze created by the flapping of butterfly wings in China changes the course of the ball. But all of the randomnesses of the game works both ways – it can cause a batter to get a great hit or nothing.

The difference between me, who would probably bat 0.00001 in Major League Baseball or someone who hits 0.350 isn’t randomness, it’s the skill and physical attributes of that player. 

So let’s take my analogy back to vaccines – effectiveness isn’t a stochastic process, it’s based on the right choice of antigens, the timing of the vaccination, and many other factors that escape my reptilian mind. 

If you get the seasonal flu vaccine, you have a greater than zero chance of not contracting the flu, because of the vaccine, not because of a flip of a coin. If you don’t get the vaccine, then you will have a substantially higher risk of contracting the flu, approaching 90% if you’re in an area that has a particularly severe outbreak. 

In other words, the flu vaccine can reduce your risk of flu by 28-49% at least, and frankly, in baseball, you’d get a $15 million contract if you hit that well. One more thing – if I had purchased a baseball team for $2 billion, the first thing I’d be doing is making certain that every player on the team got his flu vaccine. I don’t want to see a bunch of players get hit with the flu, like when a mumps outbreak hit an ice hockey team a few years ago

Flu vaccine facts – the flu is dangerous

Yes, you read that right, it’s dangerous.

Part of the problem is many people conflate the common cold with the flu. Other than being caused by viruses, the are fairly different

flu vaccine facts

Flu is a much more serious disease with more intense symptoms. 

But the complications from the flu are what separate it from the cold. During the 2018-19 flu season, 129 American children died of the flu. But, there’s more:

  • 37.4 – 42.9 million Americans contracted the flu
  • 17.3 – 20.1 million of those had a medical visit because of the flu
  • 531-647 thousand of those had to be hospitalized as an inpatient
  • Finally, 36,400 – 61,200 died
  • Worldwide, it is estimated that there will be approximately 290-650 thousand deaths. 

That makes the flu one of the leading causes of deaths for humans. Think about that.

Flu vaccine facts – the flu vaccine doesn’t give you the flu

One of the most pernicious flu vaccine myths is that somehow, in some magical way, the vaccine gives one the flu. It doesn’t.

First, the flu vaccine takes time, around 10-14 days, to induce a complete immune response. Thus, some people may contract the flu after receiving the vaccine, but they then blame the vaccine for giving them the flu. Correlation does not mean causation. It’s simply bad luck (back to math again).

Second, the flu vaccine, by its very nature, induces an immune response, so that you are protected against the influenza virus. But the virus in the vaccine is inactivated – it confers immunity but is not infectious. There is no way that a flu shot can give you a living, replicating influenza virus.

Third, the flu vaccine does have side effects that include feeling “under the weather.” It is temporary and a whole bunch less serious than actually getting the flu. In fact, part of the immune response to the flu antigen will often give a feeling of being sick, but it’s not even close to being like the real flu.

Obligatory cute cat photo. Not Bias Cat. Photo by Ramiz Dedaković on Unsplash.

Flu vaccine facts – the flu vaccine doesn’t contain mercury

Despite the whole “mercury” trope pushed by the anti-vaccine activists, it really has zero bases in fact, especially with respect to the flu vaccine

First, and most importantly, this flu vaccine myth tries to conflate elemental mercury, which is dangerous, with the ethyl mercury compound called thimerosal (or thiomersal if you speak non-American English). This would be like saying that table salt, which is sodium chloride, is dangerous because it contains sodium, an explosive metal, and chlorine, a highly poisonous gas.

That belief is a massive failure in the understanding of basic chemistry. Molecules, combinations of atoms, often have completely separate biological activity than what is seen with elements. If you inhaled pure chlorine, you would probably die. If you consume a reasonable amount of sodium chloride, you’ll be fine, because chlorine, in this case, has different properties as an ion in solution.

Secondly, only multi-use vials (generally, 10 shot vials) contain thimerosal. Why? Because thimerosal has one purpose in life, to prevent bacterial contamination. Multi-shot vials mean that 10 separate syringe needles are pushed into the vial, each with a chance of introducing bacterial contamination. Without thimerosal or another anti-bacterial agent, the vaccine could be contaminated and harm the patient.

And that’s all folks, sort of

There are many other anti-vaccine myths about the flu vaccine that are embraced by vaccine deniers. And of course, there’s Mark Crislip’s epic rant about healthcare workers who deny the flu vaccine. They are all wrong, contradicted by flu vaccine facts.

Get the flu vaccine. It might save your life or the lives of those whom you love.


  1. The reason they do this separately is that the flu circulates during the winter (mostly), and the flu season is offset by six months between hemispheres. 


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