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Low 2012–13 Influenza Vaccine Effectiveness Associated with Mutation in the Egg-Adapted H3N2 Vaccine Strain Not Antigenic Drift in Circulating Viruses

Figure 1

Specimen exclusion for influenza vaccine effectiveness analysis, Canada, 2012–13 sentinel surveillance system.

NOTE: exclusions shown here in stepwise fashion to arrive at total case and control tally (i.e. those meeting multiple exclusion criteria are counted on the basis of the first exclusion criterion met in the list shown). Missing collection dates were imputed as the laboratory accession date minus two days, the average time period between collection date and laboratory accession date for records with valid data for both fields.

Figure 1