TABLE 4.

HI titers of pandemic H1N1 2009 influenza virus-positive and Sw/Kor/CAN01/04 virus-positive sera collected from August to December^a

Range of HI titers of positive sera	No. of sera positive for:
	Sw/Korea/CAN01/04	Sw/Korea/SCJ01/09
20-40	27	14
80-160	26	20
320-640	17	28
1,280-2,560	2	10
Total	72	72

^aLimit of detection for the HI assays was set to <20 HI units, and HI titers are expressed as the reciprocal of the highest dilution of serum that inhibits 8 HA units of virus (e.g., as 80 vs 1:80).