Table 1.

 Changes in s‐IgA levels against viral antigens and neutralization activity in nasal washes and in serum levels of IgG antibodies and HI titers of IAV‐infected patients during follow‐up

Days after onset of illness	Within 3 days (<3 days)	4–21 days (<21 days)	22–300 days (<300 days)	>300 days
Nasal lavage fluid (U/μg total IgA × 100)
s‐IgA against A/H1N1	5·9 ± 2·9	31·4 ± 32·0*	17·9 ± 10·4*	8·6 ± 4·3
s‐IgA against A/H3N2	4·3 ± 1·3	20·9 ± 19·0*	21·0 ± 11·3*	10·4 ± 4·9
Neutralization activity against A/H1N1 (titer)	6·0 ± 10·8	40·3 ± 47·6**	27·9 ± 4·1	6·0 ± 2·8
No. of samples	8	16	9	4
Sampling after onset of illness (days)	1·4 ± 1·0	9·6 ± 3·3	143 ± 70	368 ± 25
Serum (U/ml)
IgG against A/H1N1	420 ± 324	858 ± 366*	837 ± 375**	1019 ± 628
IgG against A/H3N2	493 ± 456	847 ± 412	794 ± 353	657 ± 211
HI titer against A/H1N1	44 ± 32	89 ± 155	34 ± 19	47 ± 31
HI titer against A/H3N2	41 ± 49	37 ± 35	40 ± 16	53 ± 23
No. of samples	8	16	10	3
Sampling after onset of illness (days)	1·4 ± 1·0	9·6 ± 3·3	146 ± 66	370 ± 31

Values are mean ± SD.

*P < 0·01, **P < 0·05 versus the values of within 3 days.