An approximation of herd effect due to vaccinating children against seasonal influenza – a potential solution to the incorporation of indirect effects into static models

Table 2 Point estimates for relationship between risk of infection in unvaccinated population and vaccine coverage

A. Effective coverage in children	0.0%	21.00%	35.00%	45.65%	49.00%	60.00%	62.30%
Proportion of children in the total population, for estimating B.		25.78% [24]	25.78% [24]	35.70% [11]	25.78% [24]	21.08% [29]	25.78% [24]
B. Change in effective coverage in entire population (induced by varying levels of effective coverage in children)	0.0%	5.41%	9.02%	16.30%	12.63%	12.65%	16.06%
Study and population analysed
Vynnycky et al. (2008) [29]	1.00					0.44
Influenza A, 15–44 years, minimum	1.00					0.44
Vynnycky et al. (2008) [29]	1.00					0.05
Influenza A, 15–44 years, maximum	1.00					0.05
Loeb et al. (2010) [11]	1.00			0.39
Entire (unvaccinated) population	1.00			0.39
Halloran et al. (2002) [24]	1.00	0.80	0.59		0.42		0.29
Unvaccinated children	1.00	0.80	0.59		0.42		0.29
Halloran et al. (2002) [24]	1.00	0.77	0.58		0.41		0.28
Adults	1.00	0.77	0.58		0.41		0.28
RR estimates from fitted general linear equation
A. In unvaccinated remainder of children *	1.00	0.75	0.58	0.45	0.41	0.28	0.25
B. In other age groups **	1.00	0.75	0.58	0.24	0.41	0.41	0.25

Point estimates for relationship between relative risk of infection in unvaccinated population as a function of (A) effective coverage in children, and (B) change in effective vaccine coverage in entire population induced by varying levels of effective coverage in children, and the corresponding RR estimates from the fitted general linear equations.
*RR _{unvaccinated children} = 1–1.2031*effective coverage in children.
**RR _{other age groups} = 1–4.6656*(effective coverage in children)* P _children.

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