Figure 2.

Percentage histogram of influenza A(H3N2) cases (overall and clade-specific) and controls by single year of age and vaccination status, Canadian Sentinel Practitioner Surveillance Network, 2018/19 (n = 1,993)

CI: confidence interval; VE: vaccine effectiveness.

Age distributions are displayed for unvaccinated (left side) and vaccinated (right side) study participants for A(H3N2) cases overall (panels A and B), for clade 3C.2a1b (further stratified by cases with T135K or T131K substitution) (panels C and D) and for clade 3C.3a (panels E and F). The percentages of all influenza A(H3N2) cases belonging to a given single year of age are displayed as coloured bars. The same information for influenza test-negative controls is superimposed as a dotted line to indicate the sampling distribution; note that the control distribution is the same in each panel. The p values displayed are for the comparison between median ages of cases and controls within the same season. Vaccination status is based on self-report (or by parent/guardian) of receiving at least one dose of influenza vaccine at least 2 weeks before onset of influenza-like illness.