Table 4.
Estimates of VE when the latent and infectious periods are not constant from 200 simulated influenza outbreaks
| Mean Length of Latent and Infectious Periods | Scenario | Value | V E M L H | V E M LC | V E M L O |
|---|---|---|---|---|---|
| L̄ = 2, Ī = 4 | All vaccinations (50%) occurred prior to the study | True | 0.477 | 0.747 | 0.607 |
| Estimate (95% CI) | 0.474 (0.349, 0.599) | 0.703 (0.635, 0.770) | 0.602 (0.546, 0.657) | ||
| Bias | −0.003 | −0.044 | −0.005 | ||
| SE (Empirical) | 0.064 | 0.035 | 0.028 | ||
| SE (Bootstrap) | 0.074 | 0.031 | 0.032 | ||
|
| |||||
| Vaccinations occurred prior to the study (25%), in month 1 (15%), and in month 2 (10%) | True | 0.471 | 0.745 | 0.606 | |
| Estimate (95% CI) | 0.470 (0.327, 0.612) | 0.699 (0.630, 0.768) | 0.600 (0.531, 0.669) | ||
| Bias | −0.001 | −0.046 | −0.006 | ||
| SE (Empirical) | 0.073 | 0.035 | 0.035 | ||
| SE (Bootstrap) | 0.070 | 0.034 | 0.033 | ||
|
| |||||
| L̄ = 2.7, Ī = 5 | All vaccinations (50%) occurred prior to the study | True | 0.469 | 0.745 | 0.605 |
| Estimate (95% CI) | 0.440 (0.303, 0.577) | 0.679 (0.617, 0.740) | 0.589 (0.542, 0.636) | ||
| Bias | −0.029 | −0.066 | −0.016 | ||
| SE (Empirical) | 0.070 | 0.031 | 0.024 | ||
| SE (Bootstrap) | 0.074 | 0.028 | 0.027 | ||
|
| |||||
| Vaccinations occurred prior to the study (25%), in month 1 (15%), and in month 2 (10%) | True | 0.462 | 0.743 | 0.604 | |
| Estimate (95% CI) | 0.442 (0.298, 0.559) | 0.657 (0.584, 0.720) | 0.575 (0.525, 0.623) | ||
| Bias | −0.020 | −0.086 | −0.029 | ||
| SE (Empirical) | 0.067 | 0.035 | 0.026 | ||
| SE (Bootstrap) | 0.075 | 0.033 | 0.030 | ||
Bias of VE estimates were calculated allowing the latent and infectious periods to follow a distribution. V E M L H, V E M LC, and V E M L O denote VE estimates using the maximum likelihood approach against household, community, and overall transmission, respectively. We considered two situations. First, the mean length of the latent (L̄) and infectious (Ī) periods were L̄ = 2 and Ī = 4 (i.e., they were correctly specified). Second, L̄ = 2.7 and Ī = 5 (i.e., they were misspecified). In both situations, during the estimation procedure, it was assumed that L=2 and I=4. VE estimates were obtained from 200 simulations under two different vaccination scenarios. SEs were calculated empirically and by parametric bootstrap.