A friend of mine tried to say that people shouldn't take vaccines because people who receive flu vaccines year after year can sometimes show reduced protection. This effect has been dubbed the "Canadian Problem".

People who receive flu vaccines year after year can sometimes show reduced protection, an effect that Canadian infectious disease specialists say muddies public health messages for annual flu vaccine campaigns.

The article talks about how the body is too busy fighting off the flu vaccine, that it gets the flu running around?

Sure, nothing in here says "well, don't take the vaccine", but has this effect been validated, or debunked?

1 Answer 1


The article you quote says that several studies have been done that confirm the 'Canadian effect', so I think we can take it as true. However it's important to note that it is specific to the 2009 H1N1 flu strain. There is no evidence that the effect would be repeated with other flu strains, pandemic or otherwise. There is no possible way to interpret this as indicating any reason to not take the flu vaccine.

  • Many studies tried to look at the "Canadian effect". A few saw similar effects; more failed to see any effect. There's no consensus in the field on why the differences. It's certainly dishonest to not mention the contrary findings, though.
    – iayork
    Commented Dec 28, 2015 at 13:41
  • @iayork If you can cite references for that it would make a good answer. Commented Jan 1, 2016 at 18:43
  • There are too many to list individually but I'll add links to a couple reviews. You can add them to your answer if you want. I would recommend changing or deleting your answer, because as it is it is misleading in its endorsement of the original study.
    – iayork
    Commented Jan 1, 2016 at 19:13
  • Canadian study, early response and summary of other studies, review of multiple studies, another review. Should be enough to get started, there are many, many more followups
    – iayork
    Commented Jan 1, 2016 at 19:21
  • I would recommend writing your own answer using those links. Commented Jan 1, 2016 at 22:59

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