Design of field trials for the evaluation of transmissible vaccines in animal populations
Table 2
Estimated overall protection or risk difference from and required sample sizes, NT*, for trials comparing a transmissible vaccine to a traditional vaccine when clusters have overdispersed contact structures. Prior to the outbreak, α%=5% of each cluster is vaccinated with either a transmissible or traditional, non-transmissible vaccine. The contact structure is moderately overdispersed (k=1) and trials are anticipatory. The estimand of interest is noted in the first column: Δ1(5) refers to the overall protection, Δ3(5) refers to the spillover protection, θ1(5) refers to the difference in risk of infection for indirectly vaccinated animals in the transmissible case compared to those unvaccinated in the traditional case, and θ2(5) refers to the difference in risk of infection for never vaccinated animals in the transmissible case. Vax. Eff. is the true direct efficacy of the vaccine to decrease susceptibility of vaccinated animals. R0,v refers to the R0 of the vaccine. Estimate Protection or risk difference is the mean estimate of the noted estimand comparing transmissible vaccines to traditional vaccines. <.> indicates the mean 95% confidence interval width. Req. sample size from simulation, NT* is the number of clusters and number of animals required to estimate the effect in order to achieve at least 80% power. Power is the percentage of simulations with a p-value ≤ 5% across 1000 trial simulations. Type I error is the percentage of simulations with a p-value ≤ 5% across 3000 trial simulations for this sample size with a traditional vaccine.