We estimate that the effect of vaccination in the US reduced the illness attack rate from about 23% to about 20%.
The biggest impact of vaccination would have been in the temperate northern hemisphere, reducing the illness attack rate from 16% to 9%.
We summarize the impact of different diagnosis delays and diagnosis coverages on the overall illness attack rate and the peak daily incidence in Table 1.
We have used "illness attack rate" or "attack rate" to mean the proportion of the population who experience symptomatic infection, while "infection rate" refers to the proportion who were infected with symptomatic or asymptomatic infection.
With a minimum diagnosis coverage of 10% none of the antiviral drug strategies can contain the epidemic i.e. reduce the illness attack rate to less than 10% of the population.
As might be expected, our results indicate that a higher case diagnosis coverage will reduce the final illness attack rate and the peak daily incidence, as shown in Figures 3A and 3B.
Modelling studies oriented to H5N1 have been used to determine their effectiveness in reducing illness attack rates; examples include reducing illness amongst health care workers [7], [8] and in the wider community [9], [10], [11], [12], [13].
In addition, our models predicted that the temperate northern hemisphere would have had considerable reduction in the influenza illness attack rates had vaccine been distributed in the quantities indicated, i.e., rapid 50% coverage, on October 1.
Our simulation experiments allowed us to quantify reductions in the overall illness attack rate and in the maximum daily case load under a range of diagnosis delays and diagnosis coverages for both treatment-only and treatment plus prophylaxis strategies.
Baseline parameters were chosen to give rise to an epidemic with the following characteristics: an R0 of 1.5 giving a final illness attack rate of 34%, with 43% of infections occurring in households, 29% in schools and workplaces, and 26% from community contact.
However, child sequestering still decreased illness attack rates by >75% from base cases.
