4Flu - an individual based simulation tool to study the effects of quadrivalent vaccination on seasonal influenza in Germany

Table 5 Sensitivity analysis exploring the influence of the duration of naturally acquired immunity D _I

D _I	Influenza A		Influenza B			Prevented
D _I	No vaccination	TIV or QIV	No vaccination	TIV	QIV	QIV-TIV	%
4	12644	6965	6743	4302	3785	517	4.6
4	(12548–12740)	(6896–7035)	(6681–6805)	(4256–4349)	(3741–3829)	(490–545)	(4.3-4.8)
6	9820	5597	5229	3346	2951	395	4.3
6	(9750–9891)	(5550–5643)	(5183–5275)	(3313–3379)	(2920–2982)	(376–414)	(4.1-4.5)
8	8482	4944	4474	2924	2595	329	4.1
8	(8385–8579)	(4878–5010)	(4410–4539)	(2879–2970)	(2552–2638)	(305–354)	(3.8-4.4)
10	7682	4524	4055	2631	2363	267	3.7
10	(7585–7780)	(4460–4589)	(3990–4119)	(2585–2676)	(2320–2406)	(243–291)	(3.3-4.0)
12	7209	4259	3766	2476	2194	282	4.1
12	(7110–7307)	(4195–4323)	(3702–3831)	(2432–2520)	(2152–2236)	(257–306)	(3.7-4.5)

Average annual results (with 95% confidence intervals) obtained for the 20 year evaluation period (calculated from 1,000 simulations for each combination of D _I and vaccination strategy in a simulated population of about 80,000 individuals (2,000 simulations each for the baseline value of 6 years; boldface line). The immunity loss rate (baseline value 1/(9.13 years)) is varied to obtain the average duration of immunity given in the D _I column; these values apply to A(H1N1) and to the B lineages. Due to the higher drift frequency, the resulting durations for A(H3N2) are lower: 3.2 years, 4.5 years, 5.5 years, 6.4 years and 7.1 years, respectively. The last column shows what percentage of all influenza A and B infections which occur under TIV vaccination can additionally be prevented by QIV.