Table 1. Incidence rate differences (IRDs) and incidence rate ratios (IRRs) for paediatric hospitalizations for pneumonia and empyema before and after the introduction of the 7-valent pneumococcal conjugate vaccine, Australia.

Age group (years), by disease category	July 1998 to June 2004				July 2005 to June 2010				IRDc (95% CI)	IRRd (95% CI)
	PY	Hospitalizations	Incidencea		PY	Hospitalizations (no.)		Incidencea
						Expectedb	Observed
All pneumonias
0–19	31 846 901	78 552	2467		27 713 068	68 356	53 052	1914	−552 (−576 to −529)	0.78 (0.77 to 0.78)
< 1	1 499 975	10 894	7263		1 388 287	10 083	5938	4277	−2986 (−3160 to −2811)	0.59 (0.57 to 0.61)
1–4	6 186 032	42 258	6831		5 346 009	36 520	27 534	5150	−1681 (−1770 to −1592)	0.75 (0.74 to 0.78)
5–9	8 064 185	14 333	1777		6 726 493	11 955	10 667	1586	−192 (−233 to −150)	0.89 (0.87 to 0.91)
10–14	8 084 575	5785	716		7 011 457	5017	4510	643	−72 (−99 to −46)	0.90 (0.86 to 0.93)
15–19	8 012 134	5291	660		7 240 822	4782	4403	608	−52 (−78 to −27)	0.92 (0.88 to 0.96)
Bacterial pneumonia
0–19	31 846 901	71 338	2240		27 713 068	62 078	44 822	1617	−623 (−645 to −600)	0.72 (0.71 to 0.73)
< 1	1 499 975	9364	6243		1 388 287	8667	4761	3429	−2813 (−2973 to −2654)	0.55 (0.53 to 0.57)
1–4	6 186 032	37 493	6061		5 346 009	32 402	21 716	4062	−1999 (−2081 to −1917)	0.67 (0.66 to 0.68)
5–9	8 064 185	13 707	1700		6 726 493	11 433	9819	1460	−240 (−281 to −199)	0.86 (0.84 to 0.88)
10–14	8 084 575	5614	694		7 011 457	4869	4279	610	−84 (−110 to −58)	0.88 (0.84 to 0.91)
15–19	8 012 134	5160	644		7 240 822	4663	4247	587	−58 (−82 to −33)	0.91 (0.87 to 0.95)
Viral pneumonia
0–19	31 846 901	7223	227		27 713 068	6285	8230	297	70 (62 to 78)	1.31 (1.27 to 1.35)
< 1	1 499 975	1530	1020		1 388 287	1416	1177	848	−172 (−243 to −102)	0.83 (0.77 to 0.90)
1–4	6 186 032	4765	591		5 346 009	3159	5818	1088	318 (283 to 354)	1.41 (1.36 to 1.47)
5–9	8 064 185	626	78		6 726 493	522	848	126	48 (38 to 59)	1.62 (1.46 to 1.80)
10–14	8 084 575	171	21		7 011 457	150	231	33	12 (6 to 17)	1.56 (1.27 to 1.91)
15–19	8 012 134	131	16		7 240 822	118	156	22	5 (1 to 10)	1.32 (1.04 to 1.68)
Empyema
0–19	31 846 901	274	9		27 713 068	238	321	12	3 (1 to 5)	1.35 (1.14 to 1.59)
< 1	1 499 975	35	23		1 388 287	32	48	35	11 (−1 to 24)	1.48 (0.94 to 2.36)
1–4	6 186 032	96	16		5 346 009	83	146	27	12 (6 to 17)	1.76 (1.35 to 2.30)
5–9	8 064 185	39	5		6 726 493	33	31	5	0 (−2 to 2)	0.95 (0.57 to 1.57)
10–14	8 084 575	29	4		7 011 457	25	35	5	1 (−1 to 4)	1.39 (0.83 to 2.36)
15–19	8 012 134	71	9		7 240 822	64	61	8	0 (−3 to 3)	0.95 (0.66 to 1.36)

CI, confidence interval; PY, person–years.

^a Hospitalizations per million (10⁶) person–years.

^b The number of hospitalizations expected in the post-vaccine period was derived by multiplying the hospitalization incidence rate in the pre-vaccine period by the number of person–years in the post-vaccine period.

^c IRD is the incidence rate in pre-vaccine period minus incidence rate in post-vaccine period

^d IRR is the incidence rate in post-vaccine period divided by incidence rate in pre-vaccine period