Direct and indirect effects of influenza vaccination

BMC Infectious Diseases

Table 1 Simulated number of symptomatic cases (pooled over 10 years, 2017–26) for children, for adults and for the total German population

Age group	Symptomatic cases over 10 years			Effects: direct effect in children d_C = I_V indirect effects I₀ - (I_S + I_V) in children (i_C), adults (i_A) and the total population (i_T)
Age group	Sim. 1: I₀ (no additional vaccinations)	Sim. 2: I_S (with additional protective QLAIV vaccinations)	Sim. 3: I_V (with additional non-protective vaccinations)
Children (target group)	10,315,818	6,826,372	1,080,655	d_C = 1,080,655 i_C = 2,408,791 ratio for children only: i_C / d_C = 2.2
Adults (non-target group)	30,560,738	25,024,812	0	i_A = 5,535,926
Total population	40,876,556	31,851,184	1,080,655	d_C = 1,080,655 i_T = 7,944,717 ratio for total population: i_T / d_C = 7.4

The 2nd column shows the results if QIV is used with unchanged baseline vaccination coverage (reference scenario). The 3rd column shows what happens if 20% QLAIV vaccination of 2–17 year old children is used in addition to the baseline QIV coverage of other age-grous. The 4th column shows what happens if the same strategy is used as in the 3rd column with a non-protective vaccine instead of QLAIV. The 5th column shows the calculations of direct and indirect effects and of ratios. For numerical results with different QLAIV coverage, see Additional file 1: Table S3

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