ba Mahmud 2011.

Methods	Pandemic vaccines: population‐based case‐control study assessing the effectiveness of the pandemic H1N1 and seasonal TIV used during the 2009 mass vaccination campaign in Manitoba (Canada) in preventing laboratory‐confirmed H1N1 infections. Study uses data from Cadham Provincial Laboratory (CPL) and the Manitoba Immunization Monitoring System (MIMS). All Manitoba residents ≥ 6 months of age who had a respiratory specimen tested at CPL for H1N1 were included in the study.
Participants	Any adult or child ≥ 6 months of age who normally resides in Manitoba and who had a respiratory sample submitted to CPL for  influenza testing during the study period was eligible for inclusion in the study. The study was conducted from 2 November 2009 (1 week after the start of mass vaccination in Manitoba) to 10 February 2010.   Description of cases Cases were individuals who tested positive for pandemic H1N1 influenza A by reverse transcriptase‐PCR (RT‐PCR). RT‐PCR assay developed by the National Microbiology Laboratory.   Description of controls Controls were individuals who tested negative for both influenza A and B. Information on receipt of TIV or H1N1 vaccine was obtained by record linkage with MIMS, the population‐based, province‐wide immunisation registry. The date of specimen collection was considered the "index date".   Exclusion criteria 12 individuals were excluded because they tested positive for influenza A but not for H1N1.
Interventions	For all cases and controls, information on the receipt of the pandemic H1N1, TIV, and the polyvalent pneumococcal polysaccharide (PPV23) vaccines during or before the 2009/10 season was obtained from MIMS, the population‐based, province‐wide registry recording virtually all immunisations administered to Manitoba residents since 1988. Estimates of the completeness and accuracy of the recorded vaccination information are high. Vaccinated individuals were classified into 3 groups depending on whether vaccination had occurred 1 to 6, 7 to 13, or ≥ 14 days before the index date.
Outcomes	Laboratory‐confirmed influenza
Funding Source	Government
Notes	The authors conclude that "Overall, we found that the adjuvanted H1N1 vaccine was 86% effective in preventing laboratory‐confirmed H1N1 infections when received ≥ 14 days before testing, although effectiveness seemed lower among persons aged ≥ 50 years (51%) and among those with immunocompromising conditions (67%). We demonstrated that the adjuvanted H1N1 vaccine used during Manitoba’s mass vaccination campaign was highly effective against laboratory‐confirmed H1N1 infections, especially among children and younger adults. Despite logistical and communication challenges to vaccine delivery during the campaign, vaccine effectiveness appears comparable to that observed for influenza vaccines during non‐pandemic seasons in years with good antigenic match. This study demonstrates the utility of laboratory information systems and administrative databases for evaluating the effectiveness of influenza vaccines". A well‐conducted and well‐reported case‐control study
Risk of bias
Bias	Authors' judgement	Support for judgement
CC‐Case Selection	Low risk	Record linkage
CC‐Control Selection	Low risk	Drawn from the same population
CC‐Comparability	Low risk	Adjustment by confounding factors
CC‐Exposure	Low risk	Secure record
Summary assessments	Low risk	Plausible bias unlikely to seriously alter the results.