Vaccines, in general, have been a massive boon to humanity. They’ve rid the world of an affliction that has plagued humanity for thousands of years in smallpox (for reference killing over 300 million people in the 20th century alone before it was eradicated), and have almost completely wiped out polio, all while preventing millions of deaths from countless other viruses every single year.

As for the flu vaccine, it’s recommended by the Center for Disease Control and Prevention (CDC), the National Institute of Health, and almost every other major health organization around the world. Despite this, outside of whether certain vaccines can give babies autism (see our article: Do Vaccines Cause Autism?), few vaccines garner as much controversy as the flu vaccine. So if vaccines are so great- and they unequivocally are, assuming you’re not a “watch the world burn” type- and the flu vaccine is so widely recommended by experts, why is there such controversy surrounding it? Today we’ll be doing a deep dive on this topic, as well as answering the question of whether the flu vaccine can give you the flu.

According the US census bureau, there are approximately 320 million people in the United States. The CDC states that about 20% of the population will be affected by the flu each year, and in 2013 in the U.S. there were around 57,000 deaths caused by influenza/pneumonia, with the CDC crediting 3,697 as dying from influenza specifically. In fact, in that same year the CDC reported that the flu was number eight on the top causes of death behind (in order) heart disease, cancer, chronic lower respiratory diseases, accidents, strokes, Alzheimer’s, and diabetes. It is estimated that if every person in the United States received a flu shot, it would cost approximately $4.8 billion and would save approximately 3,200 lives each year on top of what are already saved today at current vaccination levels, all while preventing around a whopping 100,000 hospitalizations.

As with everything, there’s a trade-off, however; this is, in part, where some of the controversy starts to creep in. In this case, if everyone were vaccinated, around a total of 320-640 people each year would hospitalized, suffer a life threatening illness, be permanently disabled or die as a result of the vaccine. On top of that, around 3.2 million per year of the total 320 million could potentially have an immune reaction causing flu-like symptoms, although more minor than the actual flu itself and the hard number on this latter point is somewhat up for debate. (It may actually be smaller, which we’ll get into later.)

To better understand these numbers and the controversy surrounding them, let’s look at what the flu is, why the flu vaccine doesn’t always seem to work, and the problems associated with creating vaccines to fight this particular deliverer-of-death.

The influenza virus is a member of the virus family Orthomyxoviridae and comes in four broad flavors- Type A, B, C and D. The flu vaccine is designed to protect you from A, B, and C. Type D will usually affect cattle and hasn’t been shown to infect people. Type A and B are the two usually causing seasonal epidemics, and they’re the two classes of viruses the seasonal vaccine is designed to protect you from. Type C will most likely cause mild respiratory illnesses and aren’t thought to be a cause of epidemics.

Type A has two subtypes; they are differentiated by the type of protein they have on the surface of the virus, Hemagglutinin or Neuraminidase. Hemagglutinin also comes in 18 different varieties and Neuraminidasse has 11; these are named H1-18 and N1-11. Combined, these classes can make up strains. Influenza type A strains are H1N1 and H3N2.

(In 2009, you might have been aware of the specific H1N1 virus. Prior to that year, H1N1 viruses circulating around the populous caused their normal web-of-woe. Unfortunately, a new strain of H1N1 began circulating causing worsened symptoms and was the first known flu pandemic in about four decades.)

Type B viruses are characterized by lineage, depending on the type of antibody they produce- Type B/Yamagata and type B/Victoria.

The annual flu vaccine will attempt to give you immunity from both H1N1 and H3N2 type A viruses, and either 1 or 2 of the type B. As previously alluded to, no current seasonal vaccine attempts to prevent type C.

This brings us to why flu vaccinations don’t always work. Due to the extremely large number of specific flu viruses, and the complexities in figuring out which ones are circulating, it’s nearly impossible to create a vaccine that will protect everyone from every type of virus. Instead, scientists will create annual flu vaccines depending on the most likely type of flu that will be circulating that year.

How do they figure out which flu virus is more likely to be circulating?

There are over 100 countries that have national influenza centers conducting year-round surveillance for flu. They send their results to five main World Health Organization research centers in Atlanta, London, Melbourne, Tokyo, and Beijing. Two times per year (in February for the Northern Hemisphere and September for the Southern) representatives from each research center meet up and review the results of studies looking at surveillance issues, laboratory results and clinical studies. They also asses the availability of vaccine viruses.

After analyzing all the data, they make recommendations for the composition of the next flu vaccine. Based on those recommendations, each individual country decides on the specific composition of the viruses included in their vaccines. (In the United States, the FDA makes the final decision on vaccines to be sold in the U.S. and the CDC collects data from five sites across the country to assess how well the vaccine is working.)

There are two main types of flu vaccines, Trivalent and quadrivalent. The former is so-named “Tri” because it protects you from three types of the flu- type A H1N1 and H3N2, and one of the B viruses; it could be either one. As for the latter quadrivalent, it simply adds the second type of B antigen to the mix. (For reference, of the estimated 157-168 million doses of vaccine available for the 2016-2017 flu season in the United States, about 96 million were quadrivalent.)

The two types of vaccines are made in one of three ways. Most use egg based manufacturing processes- they inject viruses into fertilized hen’s eggs and allow them to incubate for several days. The viruses are then removed, killed, and the antigens purified. That concoction is now a flu vaccine. More recently, the FDA has allowed these viruses to be just severely weakened, instead of killed. This allows for the vaccine to be produced as a nasal spray instead of injected. (However, for the 2016-2017 flu season the CDC issued a recommendation that this latter form of flu vaccination not be used owing to data showing it to be significantly less effective compared to other forms of flu vaccines between 2013-2016, and non-effective altogether during the 2015-2016 flu season.)

Cell based vaccines use pretty much the same process as the egg based manufacturing, except mammalian cells are called on to incubate the virus instead of eggs.

The third method uses recombinant technology. In a nutshell, they take the protein on the surface of the virus and combine it with portions of other viruses that grow well inside insect cells. Allowed to multiply inside the insect cells, the proteins from the original virus are harvested and purified for release as a vaccine.

No matter which method used, outside of potentially the relatively rarely administered nasal spray version, the vaccine will give you some level of protection against the flu.

With that background out of the way, we’ll now address the question of the hour- Can the flu vaccine give you the flu?

As you might have guessed already given our description of how flu vaccines are made, the answer is unequivocally no- you’re not going to get the flu from the flu vaccine. Beyond the process itself being perfected, extensive testing is done on the vaccine batches themselves to ensure no viable virus ever runs the gauntlet and finds its way into the solution injected into you. This fact is also backed up by countless studies looking at those who receive flu vaccines. So why are so many convinced that the flu vaccine can give you the flu?

As previously noted, the flu vaccine can, and commonly does, give you symptoms caused by an immune response. (An immune response is what you’re hoping for in the first place.) That stimulation can come with its own side effects. For instance, people may experience soreness, swelling around the injection site, muscle and joint pain, hives, rash, headache, nausea, general feelings of weakness, etc. from the flu vaccine.

If this sounds eerily like the symptoms the flu gives you, you’re correct. Usually, however, even if such a reaction does take place, it is generally much less severe than the actual flu itself. For reference here, in 2015, 86-92% of people who received the flu vaccine reported redness around the injection site; 50-59% said they had swelling; and 33-45% said itching was also a problem. Beyond the injection site, 9-15 % say they felt generally ill after getting the shot, while 10-13% said a headache also occurred.

That said, particularly these latter numbers need taken with a grain of salt. As the CDC points out, a portion of them appear to fall in line with the chance of becoming sick from every day things we come across at any given point, like other viruses, bacteria, fungi, etc. So, for example, said individual may get infected by one of the couple hundred or so viruses that cause the “common cold” around the time they get the flu vaccine, and go on to think that the vaccine gave them the flu or flu-like symptoms.

In fact, in one study with a sample size of about two thousand people, half were given a saline shot (salt-water) and half actual flu vaccines, with the result being the two groups reporting almost identical subsequent symptoms, with the exception being that those given the actual flu shots had more soreness near the injection site- the important thing for the discussion at hand being that those who reported “flu-like” symptoms (and all other excepting arm soreness) after getting the shot did so just as frequently whether they got the saline solution or flu vaccine.

Needless to say, it’s difficult to determine precisely how many people who report flu-like symptoms after receiving the flu vaccine have such symptoms because of the vaccine- correlation does not equal causation, no matter how much our brains seem pre-wired to think so.

No matter what the precise numbers really are- a very small percentage of people are generally thought to have a reaction to the flu shot that more or less feels to them like the flu, perhaps leading someone to think they got the flu from the flu shot, even though they have not.

In another scenario, similar to when acquiring a virus that gives you the “common cold” around the time of receiving the flu shot, someone might legitimately get the flu directly before or after getting the flu shot. In this case, however, it wasn’t the shot that gave them the flu; they either just acquired the live, full strength virus before their immune system had a chance to work its magic on the vaccine (which takes about two weeks) or they acquired a strain of the virus the vaccine didn’t help with.

These factors combined have led to the widespread idea that the flu vaccine can cause a person to get the flu, despite a significant amount of scientifically vetted evidence to the contrary. Again, it’s always good to keep in mind that correlation does not equal causation. And after forming such opinions, this is one of many times when one might need to fight a bit against the brain’s natural tendency towards confirmation bias and just look at what the significant amount of hard data says instead.

This may all have you wondering how the flu vaccine protects you from the flu at all given in the vast majority of cases you’re having dead viruses injected. In a nutshell, vaccines work because they trick your immune system into thinking there is a live virus present in the body.

As for the much more interesting nitty gritty details, your adaptive immune system has two types of cells, B and T cells, that seek out and destroy these viruses. B cells produce unique protein molecules (antibodies) that attach to receptor sites of antigens (in this case the flu vaccine). Once attached, they act like a red flag for T cells to recognize. Once identified, your immune system will immediately begin creating large numbers of identical cells to circulate throughout your body. They mobilize like a defending army and attempt to vanquish the enemy. Should your immune-infantry succeed, memory B and T cells will hang around for a while in case the same invader shows up later.

It’s these memory B and T cells that the vaccine is attempting to create within your body. If you get vaccinated and your body creates its memory B and T cells, when the actual flu rears its ugly head, you have the adaptive immunity to prevent the virus from being able to replicate and spread throughout your body.

Once you’re injected with a vaccine, as previously mentioned, it’ll usually take about two weeks for your immune system to work its magic and create the antibodies necessary to fight off a future flu attack. With the peak of flu season between December and February (see Why Do People Seem to Get Sick More in the Winter), you want to get the vaccine in the early fall, giving your immune system enough time to mobilize before you’re potentially exposed.

This brings us around to the question of how effective flu vaccines actually are.

This varies considerably from year to year based on how well matched a given year’s vaccine is for the strains of virus circulating, but according the CDC, from 2004-2015, the flu vaccine was effective 61% of the time against H1N1 and 33% effective against H3N2. Against type B, they were 54% effective. (It should also be noted that even if not fully effective, the symptoms a vaccinated person experiences may be somewhat less severe than those who are not vaccinated.)

This said, as you now know, there are many types of influenza viruses. The symptoms they cause are wide-ranging, from mild to deadly. Some people seek treatment for their symptoms, and many more do not. Many other types of illnesses can cause similar symptoms, leading many to say they have the flu when they, in fact, do not. Combined with the fact that to specifically diagnose the flu you need to have your blood drawn and a lab confirm it was the flu that caused your symptoms, it can be extremely difficult for researchers to nail down the exact numbers of those affected, which is why quoted numbers can, in some cases, vary a bit from study to study.

This caveat noted, as previously alluded to, the general consensus is that the flu causes between 3,000 and 49,000 deaths and 200,000 hospitalizations per year in the United States alone. The flu vaccine is currently the best weapon doctors have of preventing its spread, and its symptoms-of-suffering. The biggest concern for opponents of the flu vaccine is whether it should be recommended for everyone. (Many companies, mostly in the health industry, even require it as a condition of employment.)

Whatever side of the argument one is on, few would dispute that the flu vaccine isn’t as effective as we humans would like. Generally speaking, as previously mentioned, getting a flu vaccine is close to a coin flip in preventing you from getting the flu. And unfortunately, those who it’s most intended to protect- those over 65 and children under 2- seem to get the least protection from it.

In fact, surprisingly, one of the largest studies performed on flu vaccine effectiveness by age group in the United States, published in the Journal of Infectious Disease in May of 2015, Influenza Vaccine Effectiveness in the United States During 2012–2013: Variable Protection by Age and Virus Type, showed almost no effectiveness for those over 65. (However, there is some evidence that newer high-dose flu vaccines may lead to a stronger immune response in the elderly, potentially changing the numbers a bit, with further research needed.) As for healthy adults and older children, they see the most benefit from the vaccine. Ironically, they’re also the least likely to have serious medical complications from getting the flu to begin with.

So why is it recommended that these individuals get the flu vaccine at all then? Because, even given all this, studies have shown that for every 4000 people vaccinated against the flu, one person’s life will be saved. The CDC also points out that herd immunity helps prevent the flu’s widespread transmission. Essentially, if enough people get the vaccine, there will be a large portion of the populous that are immune to given strains; so when the flu does start to spread, there will be less of a chance of it affecting the population at large. So those elderly who it would appear the vaccine isn’t particularly effective for will at least get some level of protection via being less likely to encounter the flu if most everyone around them is vaccinated against the projected major strains of the virus in a given year.

Given this, how are there still any real opponents to flu vaccination?  Beyond those using faulty data and/or questionable logic, or just being generally anti-vaccine regardless of what any data says, there are some who have more legitimate concerns. While you may not get the flu from the flu vaccine, we said near the beginning of this article that some people die from getting the flu shot- a much worse prospect altogether.  So what’s going on here? Like any immune response, there are those who can have an over-reaction to the flu vaccine. Although extremely rare, the CDC states serious reactions- those defined as causing hospitalization, life threatening illness, permanent disability or death- occur in 1-2 people for every 1 million vaccinated. Yes, an almost literal case of “a one in a million shot.” In the words of Lloyd Christmas from Dumb and Dumber, “So your telling me there’s a chance?!?!”

Another condition, known as Guillain-Barré syndrome occurs in about 1 person per million vaccinated. This condition is where your immune system attacks your nerves leaving you with symptoms ranging from tingling and numbness and can lead to overall paralysis. (This said, a 2009 study in China looking at the administration of over 100 million doses of flu vaccine found only 0.1 cases of Guillain-Barré per million, which was oddly lower, not higher, than what would be expected of the general population who weren’t vaccinated.) Nevertheless, this is still widely cited as an exceptionally rare serious side effect of widespread use of flu vaccines, even though recent studies are beginning to cast some doubt on this notion.

If you’re starting to get a good picture on why getting a flu shot is such a hot topic, despite it being a net positive to society as a whole, there’s actually more wood to throw on the fire. Some studies show that repeated vaccinations will reduce vaccine effectiveness later on. So- get vaccinated now when you’re healthy and in your prime, potentially helping young children and the elderly in the process, if not yourself, and you could have less effectiveness as you age and start to really need the help from the vaccine. It should be noted though that there is more research that needs done here, as there are also studies using valid methodology that don’t seem to show these results. (Again, going back to how difficult it is to nail down precise numbers here without very expensive studies with massive sample-sizes or just a huge number of studies being done looking at something.) So the question of repeated dosing is still up in the air and in need of further research.

Nevertheless, opponents of the flu vaccine posit that since over half of the time the effectiveness of the vaccine is less than 50% it may not be worth it to take even a one in a million chance of being a person who has a severe reaction. On top of that, there are the potential minor reactions so many can have from the vaccine itself, when a given person may have never become infected with the flu anyway, even had they not been vaccinated- essentially causing them pain and discomfort for no net benefit to themselves. For these reasons, opponents of the flu vaccine sometimes note that it is inappropriate for any governmental organization to recommend or require its citizens to get a flu vaccine.

On the other side of the argument, proponents of the flu vaccine point out that, aside from washing your hands and covering your mouth when you cough, vaccination is the best way we have at preventing the massive number of hospitalizations and deaths that occur each year as a result of the flu- and that’s with us already benefiting from a level of herd immunity from current vaccination levels. In the extreme case of getting rid of flu vaccinations altogether, as some anti-vaccers propose, the problem would be much worse- in the worst case scenario perhaps even someday resembling such historic incidents as the 1918 flu pandemic when about 1 in 20 people (yep) on planet Earth died as a result of said flu outbreak (a strain of H1N1 influenza), with about 1 in 4 of the human population contracting the virus.

(This pandemic was so severe that another one that struck around the same time went largely unnoticed by the wider world despite killing a whopping 1 million people and affecting countless others, including leaving many trapped inside their own bodies, without the will to speak or move. Just as quickly as the disease appeared, it suddenly seemed to disappear, leaving the medical world completely stumped. It was only about a decade ago that researchers finally uncovered what seems to have caused the problem- a disease that’s actually still around today- a rare form of streptococcus- and whose symptoms start with a simple sore throat. For you hypochondriacs out there, try not to dwell on that one the next time you get strep-throat. For more on all this, see our article The Mysterious Encephalitis Lethargica Epidemic.)

In the end, even given current flu vaccines’ less than ideal effectiveness rates, the reason so many health organizations recommend everyone within certain age groups get the flu vaccine every year is that we as a society have the ability to relatively cheaply save many thousands of additional lives per year world wide on top of what is already saved via widespread flu vaccination. The main cost here is a significantly smaller number potentially having serious reactions and the rest merely suffering a mild inconvenience or no issues at all as a result of the vaccine- thus, in the vast majority of cases a tiny price to pay for saving so many people’s lives every year. Of course, opponents of flu vaccines argue that those precious handful pay the ultimate price in saving the lives of a much greater number each year- like the lotto, it probably won’t be you that “wins,” but somebody will.

Someday, the occasional heroes that are the beaker-geeks of the world might be able to create a universal flu vaccine to prevent all types of influenza viruses from causing their meshwork of mayhem- perhaps not long after even ridding the world of this occasional plague of humanity altogether, as humanity has done with smallpox. Until that day, there will undoubtedly be controversy surrounding the flu vaccine, particularly when mandatory flu vaccination programs are occasionally pushed.

Before you decide to take the plunge on one side or the other, make sure you talk to your doctor and get the specifics of your situation- some may have good reason not to get such a vaccine, such as those already immunocompromised from illness or disease. But for most everyone else, it might hurt a little to receive a flu vaccine, but it also should help- if not you, perhaps an individual of the particularly youthful or elderly persuasion you care about.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

• It is Possible for a Person’s Muscles and Other Connective Soft Tissues to Turn to Bone
• That Time About Two-Thirds of China’s Population, and then a Decade Later About Half of Europe’s, Up and Died
• Why Native Americans Didn’t Wipe Out Europeans With Diseases
• That Time in 1374 That Thousands of People on the Streets of Aachen, Germany Suddenly Suffer from the “Forgotten Plague”, Dance Mania
• The True Story Behind The Appalling Tuskegee Syphilis Experiment

Bonus Facts:

• It’s been theorized that the eradication of smallpox and the rapid rise of HIV around the same time was no coincidence.  Both HIV and smallpox exploit the same receptor (CCR5) and, interestingly enough, the vaccine for smallpox has been shown to provide some protection against HIV as well. Thus, when the masses suddenly stopped being commonly vaccinated for smallpox, it made it easier for HIV to spread.
• Should you suffer from such a side-effect of a flu vaccine, if you live in the United States, you might be able to get compensation through the Vaccine Injury Compensation Program. In fact, over $3 billion have been paid out to those who have had injuries from the government recommended vaccines under the National Childhood Vaccine Injury Act of 1986.