The flu shot: to vaccinate or not?

Science-ish explains why getting the shot is a worthy gamble


Rich Pedroncelli/AP Photo

“… those who are so willing to inject mercury containing vaccines into people under the delusion that they are forwarding public health… should be required to submit the scientific evidence for their decisions.” — Flu vaccine statistics don’t add up, in the Nelson Star, 15/11/2011

In a world where paranoia and distrust of science abound, this op-ed in a local B.C. paper certainly fueled uncertainty around flu vaccines. In the piece, the writer suggests that public health officials and the media were deliberately misinterpreting data from a recent Lancet review about the flu shot by concluding that it’s effective for most people.

Science-ish poked around in the studies, and found a more nuanced story about the flu shot.

What’s in a flu shot?

Each year, the World Health Organization sets the flu vaccine content. Three influenza viruses—one influenza A (H3N2) virus, one seasonal influenza A (H1N1) virus, and one influenza B virus—are selected. This decision is made on the basis of a number of factors, explained McMaster University infectious diseases specialist Dr. Mark Loeb, “including surveillance data about circulating strains, how they spread, and whether there is a vaccine virus available that would provide protection against viruses likely to circulate.” For the vaccine to be most effective, he noted, there should be a match between the antigen in the vaccine and the circulating strains in a given season. So does this mean vaccination is a gamble?


The short answer is “yes.” But not so fast.

First, there is quite a bit of variation in the conclusions of studies about whether flu vaccines are effective. In the research that focuses on preventing the flu in particular populations—the elderly, those with asthma—the science isn’t all that great. This systematic review on the effectiveness of vaccination among individuals aged 65 and older concluded that the evidence wasn’t solid enough to draw conclusions, since it is mostly based on observational studies—which are at a great risk of bias—instead of good quality trials. Another review about vaccinating asthmatic patients reached similarly uncertain conclusions: “Few trials have been carried out in a way that tests whether asthma attacks following influenza infection (as opposed to following the vaccination) are significantly reduced by having influenza vaccination, so uncertainty remains in terms of how much difference vaccination makes to people with asthma.”

As for healthy adults, the evidence is more promising. A recent review on the flu shot for this group concluded that the vaccine has “a modest effect in reducing influenza symptoms and working days lost.”

Why “modest”? Well, when the vaccine matched the circulating virus, only 33 adults needed to be vaccinated to avoid one getting the flu. In “average” conditions, however, when the vaccine partially matched the circulating viral configuration, 100 people needed to be vaccinated to avoid one case of flu.

The thing is, these results aren’t so modest when considered at the population level, particularly in a year when the vaccine is well matched to the flu strains out there. “As with most preventive maneuvers,” explained Dr. Brian Haynes, chief of McMaster’s Health Information Research Unit, “a lot of people have to be treated to prevent a few cases. But a lot of deaths occur from  influenza consequences each year, mainly in vulnerable people—such as patients with chronic illnesses—who often get flu from healthier people. And then there is the 1918 flu pandemic that wiped out a lot of people.” If there was a flu-shot program then, many lives would have been saved…

Risks and benefits

As with any medication, there is evidence of potential harm—severe allergic reactions, or in the worst case, the Guillain-Barré syndrome. But the evidence strongly suggests that the benefits outweigh the harms. For one, the side-effects mentioned above are exceedingly rare (one per million vaccinations for Guillain-Barré), while the economic benefits of flu vaccine programs abound. (See this recent economic appraisal of Ontario’s universal flu immunization program, and this recommendation statement on prevention of influenza in the general population.)

There are indirect benefits related to the flu shot, too. This 2010 randomized trial involving 947 Canadian children and adolescents who received flu vaccine and 2,326 community members who did not, showed that immunizing the younger cohort in the population protected unimmunized residents against the flu. So even if it’s not proven to be effective in one group, fewer people overall get sick with more immunization.

Bottom line

In a good year, when the WHO’s infectious diseases specialists get the right match, the flu vaccine is effective. “Overall, (flu) vaccines do work,” said Dr. Haynes. “I’m basing my conclusion on the studies in which well-matched vaccines appear to have a consistent effect. Of course, going into a flu season, you can’t know that the vaccine will be well matched to the flu virus that becomes prevalent.”

But medicine is an exercise of weighing harms and benefits. In this case, getting the shot is a worthy gamble—if you want to minimize your risk of getting the flu, spreading it to your elder, younger, or sickly family members, and taking sick days from school or work. As Dr. Haynes put it: “People bet on many far longer odds: lotteries, refusal to fly. And the thing is, going into a flu season, you never know what the odds are.”

Science-ish is a joint project of Maclean’s, The Medical Post, and the McMaster Health Forum. Julia Belluz is the associate editor at The Medical Post. Got a tip? Seen something that’s Science-ish? Message her at or on Twitter @juliaoftoronto


The flu shot: to vaccinate or not?

  1. Ahhh time again for the annual mad panic over flu shots complete with mention of 1918.

    • I rarely…strike that…have never…agreed with anything you’ve ever posted Emily.

      But I gave you a “like” on this one.

      The annual flu hysteria is hysterical.

  2. Anti-vaccination loons are a public health hazard all by themselves, and any paper that would encourage them is playing with fire.

  3. Why no addressing of the “mercury containing vaccines” slur?

    It’s my understanding that one ingests less mercury from a flu shot than one would from eating a can of tuna.  Is that right?

    • Separate issue not addressed here.

      The whole mercury/autism stuff was debunked, and the doctor’s license removed.

      He was the one who started the whole anti-vaccine crowd crap.

    • You are right, LKO.  I think perhaps they do not address the “mercury containing vaccines” slur because it is hard to change people’s minds once they are set against vaccination.  That is why they removed all the perservative from the pediatric vaccines and I believe they will continue to move toward packaging vaccines in single dose vials which don’t require the perservative (mercury-based Thimersol) even though it will cost a lot more money.
      I wonder if all those people getting tatoos, realize that there is Thimersol in their tatoo ink?

    • it isnt being injected directly into your tissues..

      • Just because a substance is injested rather than injected does not make it less harmful.  In fact, if you look up mercury poisoning, you will see that Jeremy Priven and others have suffered from mercury poisoning from eating too much sushi and seafood.  However, you will be hard pressed to find a record incidence of anyone who has gotten mercury poisoning from a vaccination that contains Thimersol as a preservative.

    • Wrong. If you open a case of tuna it isn’t classified as a toxic substance. If you dropped a carton of serum on the floor and it broke open it would be.

      • Gee. Damaged vaccine is treated differently than an opened can of tuna!


        Clearly the entire medical community is conspiring to give us all mercury poisoning.

      • Could you provide a source for your claim that vaccine on a surface is a toxic substance.  Thank you.

    • It’s like 1/10th of what you’d get from a can of tuna, and in most cases, mercury has been removed to appease the vaccine-nuts.

  4. Thimersol is a mercury-based perservative that is used in multi-dose vaccines as an antiseptic and antifungal to keep the multi-dose vaccine safe from contamination.  It is not found in vaccines provided in single vial doses and as such is only found in a few vaccines in Canada, one of which is the influenza vaccine.  It has not been used in pediatric vaccines in Canada for many years.  
    This year if you don’t want to get the influenza vaccine in a needle, it is available in Canada in a quick and painless nasal spray.

  5. “Many people might conclude that if you are exposed to a virus and you don’t get sick, it’s because the virus didn’t stick or it was so weak, it just passed right through your system and your system didn’t notice. That’s not a correct notion,” says Alfred Hero, professor at the University of Michigan College of Engineering and author of the study, which was published Thursday in the journal PLoS Genetics.

    He continues, “There is an active immune response which accounts for the resistance of certain people getting sick, and that response is just as active as the response we all know and hate, which is being sick with the sniffles, fever, coughing and sneezing. It’s just that the responses are different.”

    Some people have naturally resilient immune systems and a powerful ability to combat invaders.

    • It makes a difference in communicability. 

  6. The bottom line is that this is a “worthy gamble” compared to lotteries and refusal to fly?  

    I’m a pretty pro-science kind of guy, but that’s a lousy argument.

    • I think what he is trying to say is that from a risk/benefit perspective, the influenza vaccine offers the possibility of many benefits for very little risk….the amount of benefit increases of course if the scientists correctly predict the prevalent influenza viruses for the season. 

  7. 43% of Americans risked their brain health for the flu shot, did you?  The CDC states that the annual flu vaccine is the “best” way to avoid catching the seasonal flu, but what many fail to realize is that there’s virtually NO valid scientific evidence to support it, in either its effectiveness or its safety. This is particularly true for key target groups for which the CDC says the flu shot is most important, like seniors, children and pregnant women!

    • I think this article speaks well to the question of effectiveness and safety of the vaccine.  The source you have cited is heavily dependent on the opinions of a retired neurologist Russell Baylock who as you will find in Wikipedia holds many views that are in opposition to what the rest of the scientific community believes.  He is very anti-vaccination and believes aspartame is the cause of multiple sclerosis. 

      • The article posted is based on the “The Cochrane Database Review”—the gold standard for assessing the scientific evidence for the effectiveness of commonly used medical interventions—has concluded that flu vaccines do not appear to have any measurable benefit either for children, adults, or seniors.

        And my sister developed Chronic Fatigue Syndrome over 20 years ago after drinking one too many aspartame diet sodas.  Aspartames involvement in autoimmune illnesses does not surprise me.

        • Yes, I did notice that “your” article sourced The Cochrane Database Review, which they called the “gold standard for assessing scientific evidence”.  Did you notice that this article sourced the EXACT same article from The Cochrane Database Review, dated July 2010 but that the authors interpreted the information in the research totally differently???

  8. I get the flu shot every year. The one year I didnt go I was in bed sick with the flu for almost 3 weeks and off work. Dont miss anymore

  9. This was a pretty good post by julia although I found some of her conclusions odd.  As the article points out, the evidence shows that populations that effectively immunize themselves benefit enormously while for a healthy individual the net personal risk probably weighs (slightly) against getting the shot although if you have loved ones in at risk categories that changes dramatically.

    In the final analysis it would seem we should all get the flu shot, but we really should be paid for doing so.

    • What do you feel would be adequate payment?

  10. No mention of the nasty effects of the mercury. Why did you even bother putting that in the article?

    • You mean the mercury that has been used in vaccines for 70 years and has never been shown to be harmful in the extremely small amounts used?

    • Yes as DirtyOldTown says, no indication that the mercury based preservative is dangerous.  It is in the article because the newspaper they lifted the headline from made the claim that the preservative was dangerous.

  11. Neither I nor any of my family members get the flu shot.  In my personal experience, anyone who gets the flu shot seems to be sicker than those who do not.  My kids & I take vitamin D on a daily basis and I use essential oils if we get sick, namely ravensara and eucalyptus.  If we start feeling ill, I administer liquid bentonite for a few days: 1/2 tsp diluted in liquid to my kids, or 1 tbsp to myself.  Through all the H1N1, strep throat & flu scares over the years, we’ve been just fine, even with direct contact with those who are infected.  So no to the flu shot.  We’ll be fine. 

    • Most healthy people don’t get the flu. That doesn’t men your homemade health regime works. It means you’re fortunate, and in the majority. And basing your observational hypothesis on “in my personal experience” discounts any credibility you may otherise have. 

  12. They compared the health risks to economic benefit.  Sorry but I am not willing to risk my health for economics.  Mercury is the second most toxic substance on earth, let’s inject it into our bodies. Mercury being toxic is a problem regardless if autism is or isn’t linked.  It is still poisoning you little by little. 

    • Sorry, but in a singlepayer health care system, that which benefits the economy of health care delivery benefits your health. The 20,000 o so fewer emerg visits every year because of free flu vaccination is pretty damned good for the system.  

    • If you are concerned about the preservative…you could use the nasal spray vaccine…no preservative – no mercury.

  13. For a modest (1% less) chance of not getting the flu against the potential risk however small, why would the average person get vaccinated. As a matter of fact a Canadian study showed the H1N1 vaccine marginally increased the risk of getting the flu.
    “In “average” conditions, however, when the vaccine partially matched the
    circulating viral configuration, 100 people needed to be vaccinated to
    avoid one case of flu.”

  14. Hi there- I am a nurse and am looking to raise awareness by creating a video to promote the flu shot.. I was hoping to connect with someone who may have experience a tragedy related to not getting the flu shot. I live in Ontario. If you or someone you may know has gone through a related tragedy and would like to raise awareness by talking about their experience please contact me at… I have three weeks to put a one minute video together so hopefully I can hear back soon!