Illness and Diseases

Invitation letters were sent to a convenience sample of 20 primary and 5 secondary schools. In 3 schools that agreed to participate, letters were distributed to the parents of 2190 children, and 54 households were enrolled. Fifteen hundred invitations were sent to households of children who are members of a local birth cohort, and 51 […]

Randomization. Randomization lists were prepared by a biostatistician (B.J.C.). Eligible study participants were randomly allocated to the TIV group or placebo group in the ratio 3:2 using a random number generator (R software). A block‐randomization sequence was generated with randomly permuted block sizes of 5, 10, and 15. More households were allocated to the TIV […]

Serum specimens were collected from study subjects at baseline immediately before vaccination (November–December 2008), 1 month after vaccination, after the winter influenza season (“mid‐season”; April 2009) and at the end of the follow‐up period (August–October 2009). Serum specimens were also collected from all household contacts at baseline, at mid‐season, and post‐season. All subjects and household […]

Trivalent inactivated influenza vaccine (TIV) is effective in preventing infection and illness associated with influenza A and B viruses in children during seasons when the vaccine components closely match circulating strains. On the basis of evidence from ecological studies, intervention trials, and simulation models, some health authorities have recommended vaccination of school‐age children against seasonal […]

Canadian investigators published the results of 4 observational studies in April 2010 that purported to show an association between the 2008 TIV and nH1N1 illness. The 4 studies were a test‐negative case‐control study based on the Canadian sentinel vaccine effectiveness monitoring system in 4 provinces, a conventional case‐control design in Quebec that used population control […]

A novel influenza A(H1N1) virus appeared in Mexico in March 2009. The prototype strain, A/California/09/2009(H1N1), was identified in April 2009, and the virus was found to have surface antigens that are distinct from those of the circulating seasonal influenza A(H1N1) virus. An early survey of antibody prevalence suggested that many persons 60 years of age […]

Because of limitations in study design and because they represented unexpected findings, we interpreted the results of this outbreak investigation as a paradoxical signal of possible concern—thought‐provoking but inconclusive and warranting further evaluation. Canadian investigators thus embarked on a series of confirmatory studies using more rigorous methods and laboratory‐confirmed outcomes through the summer of 2009, […]

There are, however, several limitations to this study warranting cautious interpretation of the results. First, the study relied upon a nonspecific clinical outcome (ILI) for defining pH1N1‐related illness. There are many causes of ILI, as evidenced by other contributing viruses identified through passive surveillance during the study period. We attempted to validate the ILI case […]

In additional sensitivity analyses based on logistic regression and restricted to the period of peak ILI activity (27 April–11 May 2009), the overall OR for 2008–2009 TIV effect adjusted for age, chronic conditions, Aboriginal status, and household density was higher (3.55; 95% CI, 1.70–7.34). When we used control subjects defined as fully asymptomatic persons rather […]

On‐reserve household participants.Two hundred twenty‐four individuals who participated in the community survey were reported as living on a surrounding reserve. After excluding individuals with unknown 2008–2009 TIV status (n=29), unknown chronic condition (n=1), or age 6 months on 31 December 2008 (n=4), the on‐reserve analysis included 191 survey participants, of whom 100 (52%) were aged