Influenza vaccines do not have satisfactory effective rates of preventing flu. Flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccine, according to the CDC. This is not considered highly effective for a vaccine.

Furthermore, there is the risk of mercury that is harmful to the body, according to Natural News.

Does it make sense for a healthy male in his early 40s to take the influenza vaccine, particularly when flu is an irritant but nowhere near deadly? Flu jabs come with mercury danger and does not sound effective. I am a lay man, so I may have miss out something important. Please correct me if I am wrong.

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    – JohnP
    Commented Jan 24, 2018 at 14:17
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    "mercury toxicity" is very variable. Eg. elemental mercury is pretty much inconsequential if ingested once. Even injecting mercury does little except mechanical blockage. Only repeated exposure allows elemental mercury to accumulate into toxic levels. On the other hand, a drop of dimethylmercury on hand wearing a latex glove is pretty much death sentence, that's how Karen Wetterhahn died. So, "contains mercury" alone says nothing, it's "what kind and how much" that matters. Just as pretty much everything, eg magnesium oxide vs magnesium citrate.
    – Agent_L
    Commented Jan 25, 2018 at 12:07
  • 3
    Uhm, "Natural News" is not exactly a reputable source. Any links from more well-known outlets?
    – user541686
    Commented Jan 26, 2018 at 2:14

6 Answers 6


In general, the benefit of flu shots is to the general population. Taking the cited value of 40%-60% from the CDC, we can say that it might be a coin toss for you personally to be protected from influenza by the shot. However, if many thousands of people take the flu shot, even if it only works on 40% of them, it helps protect the remaining population from the spread of the virus (AKA herd immunity). This is especially important to those within the population who cannot access the shot or cannot receive it due to a preexisting medical condition. As Graham Chiu's answer points out, influenza is no joke, especially for vulnerable members of the population (such as the elderly or people with certain medical conditions).

With regards to mercury in the flu shot, the specific additive is called "Thimerosal". Firstly: not all flu shots contain Thimerosal. If you feel strongly about it, ask your pharmacist for a vaccine that doesn't contain Thimerosal. The additive is a preservative to prevent bacteria or fungi from growing in multi-dose vials containing the influenza vaccine. For explanations as to why you don't need to worry about Thimerosal, see the other great answers below.

Some further information to put your mind at ease. In their article in Scientific American, Matthew F. Daly and Jason M. Glanz (a pediatrician and epidemiologist respectively at Kaiser Permanente's Institute for Health Research in Denver) have this to say about the safety of vaccines:

Because vaccines are given to huge numbers of people, including healthy infants, they are held to a much higher safety standard than medications used for people who are already sick.

From the same article:

The key facts [you] need to know, though, are that vaccines prevent potentially fatal diseases, that vaccines have a high degree of safety, and that their safety is constantly evaluated and reevaluated in a system operating independently from the pharmaceutical companies that make vaccines.

As a final note: in that article shared by the OP there are several scientifically unsound arguments and factual errors. I'm not going through the effort of refuting them all here. It is however worth pointing out that the presence of Thimerosal in vaccines is not a secret, and is well known among the scientific and medical community. In a brief search of medical literature in the medical science database PubMed.gov (free to the public, by the way) with the search terms "influenza vaccine safety" I could find no results making any claims about adverse side effects due to Thimerosal. In a database containing literally millions of independent, peer-reviewed medical scientific publications, you will be hard pressed to find any supporting the claims made in the aforementioned article shared by the OP.

In fact, this review article (where researchers summarize the results of 190 other sources on vaccine safety) had this to say on the topic of vaccine safety [paraphrased by me]:

  • Influenza causes substantial death, suffering and socioeconomic impact worldwide.
  • Vaccination is the best defense against influenza.
  • Influenza vaccines are "very safe".
  • The only known side effects of influenza vaccines are temporary nasal congestion (runny nose) and sometimes allergic reactions.
  • Allergic reactions appear in less than 1 out of every 1,000,000 doses.
  • Children with asthma under the age of 2 are particularly susceptible to the side effects of the influenza vaccine and more study is required to ensure it's safety for this particular high-risk group.

In other words, infants who have problems breathing might be more significantly affected by allergic reactions or congestion. That's all they have to say about flu vaccine side effects (regardless of whether they contain Thimerosal). Finally, a direct quote from the conclusion:

Vaccines have to meet higher safety standards, since they are administered to healthy people, mainly healthy children. The monitoring of annual influenza vaccine safety, which is particular [sic] important on account of the annual changes in the viral antigen composition of the vaccine, constitutes a critical component of the influenza vaccination program. Indeed, not only does this strategy ensure the safety of vaccines, it can also maintain public trust in the national vaccination program.

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – JohnP
    Commented Jan 24, 2018 at 14:20
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    Are you sure about the point that "The only known side effects of influenza vaccines are temporary nasal congestion"? Google (and personal experience) suggests that common side effects include soreness, redness, swelling, headache, fever, nausea, and muscle aches.
    – Shane
    Commented Jan 24, 2018 at 21:10
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    @Shane Good point. The paper's wording was "adverse events" (instead of side effects) caused by the vaccine so I guess they didn't include things that were not threatening to health. I can't tell you why they didn't include those kinds of side effects. Commented Jan 25, 2018 at 14:12
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    Herd immunity is important for many diseases, but in the specific case of the flu vaccine's ineffectiveness, I don't think herd immunity is relevant. The reason the flu vaccine is relatively ineffective is that flu strains evolve very quickly, so there's a high probability that you'll contract a strain that the vaccine doesn't help against. Since everyone is receiving a vaccine that protects against the same strains, herd immunity doesn't help with that problem.
    – ruakh
    Commented Jan 26, 2018 at 5:36
  • @ruakh If you read the link shared by the OP regarding the 40%-60% estimate you'll see the CDC says that's in seasons when it is well matched to the particular prevalent strains that season. In cases where the vaccine is well matched to the strains of flu that are spreading in that particular season, herd immunity is certainly relevant. In cases where it is not well matched, obviously it won't keep you or the "herd" from catching/spreading the flu. What you're saying is "sometimes the flu vaccine doesn't work, and when it doesn't work... it doesn't work". Commented Jan 26, 2018 at 14:17

Tackling your points in turn, in inverted order:

flu is an irritant but nowhere near deadly

You are probably confusing the flu (influenza) with the common cold, which is colloquially often called “the flu”, or gastroenteritis (colloquially called “stomach flu”). Unfortunately these are actually very different diseases. The common cold is indeed largely harmless. By contrast, influenza (and potentially also gastroenteritis) is a serious, and potentially deadly, disease. Its symptoms vary but it usually leads to high fever, strong pain, diarrhoea and difficulty sleeping. In a word, you’ll feel rotten for the better part of a week.

In addition, the mortality may not seem very high but (even ignoring that it caused the deadliest epidemic in human history) each year thousands of people die from it in the US alone. In fact, the numbers vary greatly with each season, from about 3,000 to almost 50,000.

As a healthy 40-year-old you are less likely to die from the flu but you could still get very seriously ill. Furthermore, by getting vaccinated, you contribute to herd immunity. This prevents the flu’s spread and protects other, less healthy people, from dying from the flu.

[40%–60% risk reduction] is not considered highly effective for a vaccine.

Even a 40% risk reduction is very effective. It’s maybe not considered “highly effective” compared to other vaccines because vaccines, in general, are extremely effective. But compared to other remedies, vaccines are one of the most effective treatment methods.

Rather than thinking of 40%–60% as a coin toss, think of it this way: amongst the vaccinated population, the incidence is more than halved (due to the compounding effect of reduced risk of infection in the population). This is impressive.

[The flu vaccine contains] mercury that is harmful to the body, according to Natural News.

This is intentionally deceptive: flu vaccines do not contain elementary mercury (and never have)! Some flu vaccines contain thiomersal (or “thimerosal”), which in turn contains ethylmercury. Despite its name, this is a different compound, and does not have the same chemical properties as elementary mercury.1 Contrary to what Natural News claims, thiomersal in vaccines is safe: it has never been found to produce a negative effect in humans.2

Beware of your news sources: Natural News is a scam website that lies to sell ineffective, unregulated, and potentially harmful supplements. When researching health topics, always cross-reference your information with respectable sources such as the WHO, the NHS or the CDC. You don’t need to exclusively rely on them but they accurately portray the scientific consensus and, unlike sites like Natural News, they have no financial interest in lying to the public, since they do not make profit off it. Furthermore, they are funded independently by different governments.

1 This is a very important point, so it bears explaining: Consider table salt. Table salt is the chemical compound sodium chloride. Both sodium and chloride, in isolation, are highly toxic. But when combined chemically, as in table salt, they form a harmless compound that is safe for normal consumption. The same is true for the relationship between mercury and ethylmercury.

2 As everywhere, the dose makes the poison. Thiomersal in high concentrations is toxic, just like table salt. Toxicity is often measured in LD50. Salt has an LD50 of 12357 mg/kg in humans, which means that approx. 58 tablespoons are problematic for an 80 kg man. Thiomersal has an LD50 of 75 mg/kg (in rats), which means that you’d need to vaccinate that 80 kg man over 100,000 times, at once, for a similar effect!

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – JohnP
    Commented Jan 24, 2018 at 14:18
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    "You are probably confusing the flu (influenza) with the common cold, which is colloquially often called 'the flu'" Another common confusion would be Gastroenteritis, which causes vomiting and is often called the stomach flu but is not caused by influenza.
    – Ray
    Commented Jan 24, 2018 at 17:26
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    @jpmc26 WHO/NHS/CDC... receive lots of money - Of course they do. Serving the health needs of millions of people is expensive. Since vaccines prevent disease, their use reduces the demand for health services. As for whether Natural News has an incentive to lie; as you say, if it can deliver actual results it would make a mint. However, if its products turned out to be ineffective, how else could it make a sale? Commented Jan 26, 2018 at 13:17
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    @jpmc26 It’s more that “several unrelated, governmental and intergovernmental agencies from across the world are in agreement”. You’d need to posit a world-wide conspiracy to explain why they would all publish the same lies (and, sure, some people believe that; it’s not worth arguing with them, though). Commented Jan 26, 2018 at 19:04
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    @jpmc26 I did edit that paragraph to make it clearer. But I really don’t want to tread out this purely incidental point any further. The answer is already too long, and the topic here is influenza, not the credibility of various health sources. I don’t really think I should have to argue extensively why scientific sources are superior on a health site. — That said, consensus totally is a valid argument in a discussion of whether somebody is telling the truth. The same lie being repeated by many independent sources is simply less likely. Commented Jan 26, 2018 at 19:20

Influenza deaths are not specifically tracked in those over the age of 18 but they can be estimated from death certificates.

CDC estimates that from 2010-2011 to 2013-2014, influenza-associated deaths in the United States ranged from a low of 12,000 (during 2011-2012) to a high of 56,000 (during 2012-2013). Death certificate data and weekly influenza virus surveillance information was used to estimate how many flu-related deaths occurred among people whose underlying cause of death on their death certificate included respiratory or circulatory causes.

So deaths from influenza are often from a secondary bacterial pneumonia or excessive immune response (cytokine storm) to the flu infection. Some young people can die within hours of the flu infection from the latter reason.

And if we just look at hospitalization rates we can see that for the age range 18-49, the rate of 41/100,000 is under half that of the average but twice higher than age range 5-17 years.

And 50 million deaths from the 1918 pandemic makes your statement that "flu is an irritant" completely erroneous.

Interestingly a new paradigm for managing seasonal flu has been suggested. The issue is that the people who most need the vaccination (elderly, sick, very young) are those that benefit the least from vaccination due to an impaired immune response to the vaccine, and it may be more effective to vaccinate the older young who respond well to vaccination:

Furthermore, influenza epidemiology is unfortunately characterised by dissociation between populations most likely to have severe disease (infants and elderly people), and populations most likely to benefit from vaccination (older children and adolescents—ie, those aged 2–16 years).3 Older children and adolescents seem to be important for the early propagation of influenza in populations, and the efficacy of influenza vaccines is greater in these populations than in elderly people, but they are generally not prioritised for immunisation because of their lower risk of morbidity and mortality from this infection.3 This paradoxical state of affairs has led some researchers to suggest that the best way to minimise the burden of seasonal influenza would be to focus immunisation programmes on children, adolescents, and young adults, with benefit accrued by elderly people and infants as a result of herd immunity.3

And ...

analysis highlights the importance of herd effects for decision makers: a rapidly implemented LAIV programme focused on children aged 2–16 years is actually more effective at preventing disease in elderly people than a more slowly implemented programme that includes both LAIV and direct immunisation of elderly people themselves. This finding is because a rapid, early focus on young individuals, in whom the vaccine is more effective, stops the influenza epidemic in its tracks.

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    FYI… Recent estimates published 2017 say between 291,000 and 646,000 people worldwide die from seasonal influenza-related respiratory illnesses each year. Commented Jan 23, 2018 at 4:09
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    How many of these deaths are healthy 40 year olds tho? I've always assumed all these deaths are either very young or very old and mostly people that don't have access to good medical care. To the OPs point, is there a real risk of the flu being anything other than annoying to him?
    – JPhi1618
    Commented Jan 23, 2018 at 14:28
  • The UK is now providing the vaccine to those in secondary school - ages 10-15. I don’t know if they also provide it in primary school for 4-9 year olds.
    – Tim
    Commented Jan 23, 2018 at 16:57
  • @JPhi1618 I've added a link to hospitalization rates stratified by age. Commented Jan 23, 2018 at 18:39
  • @JPhi1618 Important to note: by getting vaccinated, you would help protect the very young and very old (and the immunocompromised, of any age)
    – Alexander
    Commented Jan 23, 2018 at 20:50

Influenza vaccines do not have satisfactory effective rates of preventing flu. Flu vaccination reduces the risk of flu illness by between 40% and 60%

Vaccines aren't meant to stop diseases by making 100% invulnerable individuals. Of course we want the highest possible efficacy, but the primary benefit is the large impact they have on a collective level, by limiting the spread of a disease, so that it snuffs itself off.

It's all about reducing the basic reproduction number (R0), the number of cases of the disease that are caused by infection from one case of the desease. There are 3 ranges this number can fall into

  • 1 < R0 Each person, on average, infects more than 1 person before recovering. Disease spreads as more people get infected than people are recovering.
  • R0 = 1 Each person, on average, infects exactly 1 other person before recovering. The disease spread plateaus (i.e. the number of infected remains the same.), as the number of people getting infected exactly matches the number of people recovering.
  • 0 ≤ R0 < 1 Each person, on average, infects less than 1 person before recovering. The disease gets snuffed out over time, as people recover faster than people are getting infected.

The exponential math that models disease spread applies in many areas, such as in nuclear chain reactions, where the effective neutron multiplication factor is the average number of neutrons from one fission that cause another fission. Just as control rods are used in nuclear reactors to maintain the k around 1 (a stable, non-growning, non-dying rate of reaction), vaccines can be used to bring R0 below 1, so that deceases snuff themselves out.

Herd immunity is a proportional to the product of vaccine efficacy, and the vaccination rate. Here's a simplified visualization of herd immunity, which I think presumes 100% vaccine efficacy. We can compensate for lower vaccine efficacy by increasing the vaccination rate.

Herd immunity simulation

Not using a vaccine because it's "only" 40% - 60% effective is counterproductive: that's exactly when we need a high vaccination rate, the most!

  • 1
    Good answer with great images, except that "Vaccines aren't meant to stop diseases by making invulnerable individuals. They never have been." is just rubbish. That's not their only effect, but vaccines do not only exist for herd immunity. Vaccines are actually primarily intended to prevent the vaccinated person from getting the disease. Otherwise the HPV vaccine for example would not only be available to girls.
    – user12701
    Commented Jan 23, 2018 at 22:15
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    @MilesRout I misword that, I'll edit it. But has any vaccine ever achieved (100%) "invulnerable" status? It's a "nice to have" for sure, but vaccine efficacy has diminishing returns. Increasing efficacy from 99.0% to 99.1% wouldn't be worth it, if the same resources could have been used to cause a large rise in vaccination rates, instead.
    – Alexander
    Commented Jan 23, 2018 at 22:50
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    @MilesRout Many health professionals are proponents of routinely giving the HPV vaccine to boys for precisely this reason. The reason that this isn't currently done is a (previous, no longer) lack of studies, ethical considerations and (unfortunately) flawed economics arguments. (The situation had changed in the meantime, as there's now evidence for a beneficial effect of the vaccine in men, too.) Commented Jan 23, 2018 at 23:17
  • @Alexander of course they don't get to 100%, but it's still the goal.
    – user12701
    Commented Jan 24, 2018 at 22:24
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    @MilesRout Yes, but not at the expense of underfunding initiatives to drive up vaccination rates\
    – Alexander
    Commented Jan 24, 2018 at 23:04

Other answers have explained why being vaccinated is generally a good idea, and I fully support the ones that do. That said, the article you've linked to does indeed present some very scary points, and I fully understand why reading something like that would give you some doubts about your own safety, so I'd like to directly tackle the key point raised by it.

I have no medical qualifications whatsoever, so just like you I'm reading the information that's available as a lay person.

Mercury is toxic at any dose when injected into the body, even in micrograms.

Injecting a syringe full of mercury into your body is definitely a bad idea. The article is mostly worried about Thimerosal, which is used as a preservative. The US National Toxicology Department has tested this ingredient in response to fears, and you can see the results here. It tells us the following:

In this study, the LD50 of thimerosal in rats was 98 mg/kg

The LD50 being 98mg/kg means that, to have a 50% chance of killing a rat that weighs one kilogram, you'll need to inject 98mg of Thimerosal. Looking at this, 400g for a rat's weight seems like a reasonable estimate, so it'll take about 40mg of Thimerosal to have a 50% chance of killing a pet rat. Heading back to your article:

As you can see from this snapshot, the package insert readily admits that each vaccine dose “contains 50 mcg thimerosal (<25 mcg mercury).”

Yep, it absolutely does. Converting the units, 50mcg=0.05mg. If we want to kill that rat from Thimerosal poisoning, we'd need to inject it with 800 of these flu shots. I'm going to re-state this in big text just in case you're only skimming:

To stand a decent chance of killing a pet rat from mercury poisoning, you'd need to inject it with 800 of the flu vaccines discussed in that article, all at the same time

You're probably a lot bigger than your average lab rat, so we're talking tens of thousands of flu shots before the mercury inside it starts getting dangerous.

The article also discusses formaldehyde, and if you're interested you can do your own research into the toxicity of that and see how many flu shots you'd need to be in danger of death from formaldahyde poisoning.

It's a real shame that the articles trying to tell you vaccines are dangerous are so exciting to read, whilst articles describing actual scientific research are so dry and boring. You can see why ideas like this gain so much traction - it's terribly exciting to read! Unfortunately, it just doesn't stand up to any serious scrutiny.

  • 1
    Good points. If you're worried about scary stuff like formaldehyde, you'd end up having a very restricted diet because it occurs naturally in many foods.
    – JPhi1618
    Commented Jan 23, 2018 at 14:35
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    Also worth noting about formaldehyde: our own cells produce it as a waste product. Our renal system has no problem filtering it out and processing it into urine. I am not sure how much of it from a vaccine would overload our own natural processes for filtering it. However, Occam's razor tells me that since there are not droves of people in the ER after receiving vaccines, they probably do not contain enough to cause any problems.
    – user1241
    Commented Jan 23, 2018 at 15:51
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    For perspective, 800 flu shots would be about the same weight as the rat, maybe a little more.
    – Charles
    Commented Jan 23, 2018 at 22:24
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    "Injecting a syringe full of mercury into your body is definitely a bad idea." OK it's probably not a clever thing to do, but would it actually harm you in this form, or just be excreted?
    – RedSonja
    Commented Jan 24, 2018 at 11:41
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    Minor nitpick: the LD50 is a decent frame of reference, but it can be misleading. For substances that we metabolize and/or excrete easily, safe doses and the LD50 can be an order of magnitude apart or more. In between you have non-lethal doses that still cause significant acute harm (e.g. liver damage). For substances that we have trouble removing (such as certain heavy metal compounds), you can have chronic damage from doses multiple orders of magnitude smaller than the LD50.
    – Ian
    Commented Jan 24, 2018 at 14:43

A few more points, in addition to the good answers you already have and just addressing:

Does it make sense for a healthy male in his early 40s to take the influenza vaccine [...]?

Short answer: healthy 40-year-old male already excludes a number of high risk/priority groups, but not all of them (e.g. if you help taking care of 90- year-old grandma, maybe you don't want to risk her health).

long answer

  • Several answers above have already discussed the topic of herd immunity. The difficulty here with the flu is that it changes so rapidly that we cannot really get there (which is also the reason for the low efficacy of the flu shot and the need to develop and distribute new shots every flu season).

  • In general, whether it makes sense to try approaching herd immunity, i.e. to recommend vaccination for everyone also depends on circumstances.

    • E.g. in Germany we have no yellow fever, so vaccination is only recommended for people travelling to regions that have.
  • Now for the flu, at least with current vaccine development technology, we cannot reach true herd immunity (it changes too fast). However, if we can reduce the number of infections by half, and slow down the spread of the infection, that can make a vital difference for the health system: there are only so many patients that can be taken care of at a given time. If you can keep the number of patients below what the capabilities are, that's much better for everyone compared to situations where patients can only be put to beds in the hallway of the hospital and half of the staff is ill as well.
    From a macroscopic perspective, you can then ask what strategy is better: e.g. vaccination campaign or building more hospitals.

  • There's also an intermediate concept between full herd immunity and no vaccination: vaccinate only certain groups of people. These will typically be

    • persons more susceptible to the disesase (likely to contract and/or higher risk of (severe) complications)
    • persons that may be in the position to infect many other and/or many susceptible people (for the flu: public office, teachers, health care workers)
    • health care workers: you need them particularly when there's an outbreak of disease

    For the flu, these high risk/priority groups are:

    • Kids 6 months - 4 years (CDC)
    • People over 50 (CDC) or 60 (RKI)
    • People with certain chronic diseases (CDC and RKI)
    • Residents of retirement or nursing homes in general (CDC and RKI)
    • Pregnant women (CDC and RKI)
    • Caretakers and household contacts for high risk persons (CDC and RKI)
    • Persons with increased professional risk (health care workers, CDC and RKI), workers in public offices, teachers etc. (RKI)
    • Persons working with birds (this is in order to avoid double infection with human and avian influenza, RKI)
    • American Indians/Alaska Natives (CDC) (Lists from the documents linked below)
  • CDC decided that it is worth trying to get as many people vaccinated against flu as possible, whereas the RKI [German equivalent of CDC] has a certain groups policy
    Note that this does not necessary mean a controversy between experts, but this may be caused by regional differences.

  • Just to be complete: there are also counter-indications, but "healthy" pretty much excludes them.


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