# 4728
It was called, euphemistically, the `Canadian Problem’.
News of a controversial, yet unpublished, Canadian study that began to emerge last September suggesting those who had received a seasonal flu shot in the previous year were more susceptible to the pandemic H1N1 virus.
Helen Branswell, science and medical reporter for the Canadian Press, was among the first to report on it (see Branswell On The Canadian Flu Shot Controversy).
In a matter of days a number of Canadian Provinces halted or announced delays in rolling out the seasonal flu shot, even though the study had yet to be published (see Ontario Adjusts Vaccination Plan).
The CDC and the World Health Organization, meanwhile, stated they saw no evidence in their data to suggest a link, but that they were continuing to investigate the matter.
Since then we’ve seen conflicting information.
In early October we saw a study published in the BMJ (British Medical Journal) that suggested exactly the opposite - that getting the seasonal flu vaccination may be slightly protective against the swine flu (see When Studies Collide).
Which, admittedly, ran contrary to what we’d heard previously from the CDC, who maintained that the seasonal vaccine was not expected to offer any protection against the novel H1N1 swine flu virus.
By November, with no compelling corroboration of the `Canadian Problem’, Canada’s National Advisory Committee on Immunization (NACI) came out in favor of resuming seasonal flu jabs (see NACI: Canada Should Resume Seasonal Flu Vaccinations).
In April, writing for CIDRAP, Maryn McKenna wrote of the publication of these four controversial studies in PLoS Medicine.
New Canadian studies suggest seasonal flu shot increased H1N1 risk
Maryn McKenna
Contributing Writer
Apr 6, 2010 (CIDRAP News) – Despite a rapidly launched range of studies, investigators in Canada are still unable to say—or to rule out—whether receiving a seasonal flu vaccination in the 2008-09 season made it more likely that Canadians would become ill from 2009 pandemic H1N1 flu.
Which brings us, today, to a newly published study in Eurosurveillance on a household study conducted in Australia on the very issue.
A hat tip to Ironorehopper on FluTrackers for posting this link.
Eurosurveillance, Volume 15, Issue 28, 15 July 2010
Rapid communications
D Carcione, C Giele, L S Goggin, K S Kwan, D W Smith, G K Dowse, D B Mak, P Effler
We conducted a prospective household transmission study to examine whether receipt of 2009 trivalent influenza vaccine (TIV) was associated with increased risk of influenza-like illness (ILI) among contacts of confirmed pandemic influenza A(H1N1) 2009 patients.
In the week following onset of pandemic illness in a household member, 46 (15%) of 304 TIV-vaccinated contacts, and 174 (15%) of 1,162 unvaccinated contacts developed ILI (p= 0.95).
Receipt of 2009 TIV had no effect on one’s risk of pandemic illness.
Although one would hope for a definitive, etched-in-stone answer here, as always there are limitations to this study. In the author’s discussion, they write:
Several limitations of our study should be noted. First, the outcome sought was clinical ILI and not laboratory-proven influenza. Only a small subset of household contacts who developed ILI were tested for influenza; however, a high proportion of the contacts tested by PCR within two days of developing ILI were confirmed as having pandemic influenza A(H1N1) 2009 infection.
Second, vaccination histories were not verified through medical records. Most seasonal 2009 TIV vaccinations would have been administered between the months of March and June 2009, and interviews to determine vaccination status were conducted between late May and early August 2009. Whilst errors in recall may have occurred, it seems reasonable to assume that were this the case such errors would be similar among the cohort who later developed ILI, compared to those who did not.
While this study did not find an association – either positive or negative – to prior inoculation and contracting novel H1N1, the authors regard this as an interim analysis.
No doubt, this is a subject that will command additional study and analysis. For now, however, if there is an association . . . it doesn’t appear to be pervasive.
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