PMC

Pandemic H1N1 detections, and cumulative proportion vaccinated against pandemic H1N1 among cases and controls, by week (n=3898). Excludes specimens from patients who failed to meet the influenza-like illness case definition or had unknown status; specimens collected >7 days after influenza-like illness onset or with unknown interval; and patients with chronic conditions unknown, age unknown, or influenza test results unavailable or inconclusive on typing. One specimen positive for seasonal A/H1N1 (week 46) and four positive for seasonal A/H3N2 (weeks 33, 41, 44, and 50) are not represented on graph. Primary analysis period captures week 45 (8 November) to week 48 (5 December). Secondary analysis period captures week 44 (1 November) to week 52 (31 December). Cumulative percentages for patients vaccinated ≥2 weeks before illness onset exclude from numerator and denominator those vaccinated <2 weeks before illness onset. Figure shows cumulative percentages vaccinated from week 43 that are not directly comparable to proportions shown in table 3 for weeks 45-48