Effect of vaccination campaign start date and vaccine efficacy on overall attack rates. For a given vaccination campaign start date, the percent reduction in final attack rate relative to that observed in the absence of vaccination is presented for vaccine efficacy of between 50% and 100%. The ranges of the percent reduction in attack rates are indicated by solid lines and labeled. Vaccination campaigns were implemented weekly, starting July 5, 2009, with the last campaign started November 22, 2009. The start of the Vancouver influenza season on September 6, 2009 is indicated by a vertical line. All simulations assumed R
0 of 1.4, latent period of 3 days, and infectious period of 7 days.