Assessing the benefits of early pandemic influenza vaccine availability: a case study for Ontario, Canada

Abstract

New vaccine production technologies can significantly shorten the timelines for availability of a strain-specific vaccine in the event of an influenza pandemic. We sought to evaluate the potential benefits of early vaccination in reducing the clinical attack rate (CAR), taking into account the timing and speed of vaccination roll-out. Various scenarios corresponding to the transmissibility of a pandemic strain and vaccine prioritization strategies were simulated using an agent-based model of disease spread in Ontario, the largest Canadian province. We found that the relative reduction of the CAR reached 60% (90%CI: 44–100%) in a best-case scenario, in which the pandemic strain was moderately transmissible, vaccination started 4 weeks before the first imported case, the vaccine administration rate was 4 times higher than its average for seasonal influenza, and the vaccine efficacy was up to 90%. But the relative reductions in the CAR decreased significantly when the vaccination campaign was delayed or the administration rate reduced. In urban settings with similar characteristics to our population study, early availability and high rates of vaccine administration has the potential to substantially reduce the number of influenza cases. Low rates of vaccine administration or uptake can potentially offset the benefits of early vaccination.

Projecting influenza vaccine effectiveness: A simulation study

“…Latent period was drawn from a uniform distribution with the mean of 1.5 days within the range of 1–2 days [ 27 , 28 ]. The infectious periods for both symptomatic and asymptomatic infections were sampled from a truncated lognormal distribution with scale of 1 and shape of 0.4356, having mean of 3.38 days [ 27 , 28 ]. The probability of developing asymptomatic infection was sampled for each individual from a uniform distribution in the range 0.3–0.7 and was modified for vaccinated individuals according to the vaccine protection.…”

“…We considered a range of attack rates from low (4%) to high (40%) for calibration in the absence of vaccination, representing mild to severe influenza epidemic seasons. Latent period was drawn from a uniform distribution with the mean of 1.5 days within the range of 1-2 days [27,28]. The infectious periods for both symptomatic and asymptomatic infections were sampled from a truncated lognormal distribution with scale of 1 and shape of 0.4356, having mean of 3.38 days [27,28].…”