In this 2018 letter to the British Medical Journal, a retired pediatrician claimed that

In any discussion of influenza epidemiology we should acknowledge the careful and steady (one could even say fearless) work of Danuta Skowronski and her Canadian public health colleagues. It was they who found that the 2008-9 flu shot doubled the risk of illness from the 2009 H1N1 pandemic flu. Their observations were considered important enough to alter Canadian vaccine recommendations for the 2009-10 season. However, for some reason, they had a good deal of difficulty getting their study finally published. (Skowronski, PLoS Med 2010;7(4):e1000258)

Did the 2008-9 flu shot double the risk of getting the H1N1 flu?


1 Answer 1


According to Does Seasonal Influenza Vaccination Increase the Risk of Illness with the 2009 A/H1N1 Pandemic Virus?, wherein reference "4" is the Skowronski reference of the OP:

Given the uncertainty associated with observational studies, we believe it would be premature to conclude that TIV increased the risk of 2009 pandemic illness, especially in light of six other contemporaneous observational studies in civilian populations that have produced highly conflicting results (see Table 1 for details on study design, population sampled, and results) [10]–[15]. We note the large spread of vaccine effectiveness estimates in those studies; indeed, four of the studies set in the US and Australia did not show any association [12]–[15], whereas two Mexican studies suggested a protective effect of 35%–73% [10],[11]. The most recent Canadian study in this issue of PLoS Medicine [4] is clearly at odds with these results, with an estimated average negative effectiveness of −68% based on their Sentinel system. Only one study, set in the US military population, potentially corroborated the findings of the Canadian study [16].

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    So, In English, 4 studies did not replicate the Skowronski finding, but the US military study may have done so? Commented Nov 14, 2018 at 15:08
  • @JoshuaFrank the military study says "Patients with H1N1 virus infection were also more likely to have received influenza vaccination within the previous year (66% vs 40%; P<.01) and to have received LAIV (52% vs 28%; P<.01). " academic.oup.com/cid/article/49/12/1801/436062
    – DavePhD
    Commented Nov 14, 2018 at 15:15
  • @DavePhD The quote does not establish that there is any causal relation between flu shots and flu. Apparently, not everyone got the flu shot, or there wouldn't be a non-vaccinated group for comparison. On what basis was the flu shot administered? If it was administered to people considered more likely to get the flu, it could be somewhat effective while people with the shot got flu at a higher rate. Commented Nov 14, 2018 at 22:45
  • @DavidThornley According to the Canadian study, though the vaccine protected from other strains of the flu, it increased the risk of H1N1.
    – DavePhD
    Commented Nov 15, 2018 at 18:17

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