Table 1.

Summary of infection outcomes in terms of the numbers of escapes, symptomatic (sym.) and asymptomatic (asym.) infections, by age group and pre-season antibody level, for the influenza H3N2 epidemic during 1977–1978 and the H1N1 epidemic during 1978–1979 in Seattle.

Status Category	1977–1978, H3N2				1978–1978, H1N1
	Total	Escape	Infection		Total	Escape	Infection
			Sym.	Asym.			Sym.	Asym.
Population	741	567	121	53	479	330	98	51
Age Group
Child	401	270	94	37	259	115	95	49
Adult	340	297	27	16	220	215	3	2
Baseline antibody titer level†
1	107	69	30	8	188	81	66	41
2	210	134	57	19	177	136	31	10
3	190	155	19	16	113	112	1	0
4	227	202	15	10
Unknown	7	7	0	0	1	1	0	0

^†HI titer levels for H3N2: (1) ≤ 10, (2) 20, (3) 40, (4) ≥ 80.

HI titer levels for H1N1: (1) < 10, (2) 10 and 20, (3) ≥ 40.