Low 2012–13 Influenza Vaccine Effectiveness Associated with Mutation in the Egg-Adapted H3N2 Vaccine Strain Not Antigenic Drift in Circulating Viruses
NOTE: excludes specimens from patients failing to meet the influenza-like illness case definition or unknown; specimens collected >7 days after influenza-like illness onset or interval unknown; comorbidity unknown; age unknown or <1 year and influenza test results unavailable or inconclusive on typing. 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. One specimen diagnosed with both A/H3N2 and A(H1N1)pdm09 in week 2 is not presented in the graph. Vaccine effectiveness analysis spans week 44 to week 18.