Table 3.

Frequency of reduced susceptibility to antivirals of selected clinical isolates from Japan (2018)/2019 season.^a.

Type/subtype	Drug	Total frequency	Age group (years)
			0–11	12 –19	20–64	>65	Unknown
A(H1N1)pdm09	NAI	0.9%b (21/2252)c	1.1% (14/1329)d	0% (0/271)	0.6% (3/527)	3.7% (4/109)	0% (0/16)
	Baloxavir	2.3% (9/395)e	2.7% (7/264)	2.3% (1/44)	1.6% (1/63)	0% (0/21)	0% (0/3)
A(H3N2)	NAI	0% (0/357)	0% (0/231)	0% (0/48)	0% (0/54)	0% (0/24)	0% (0/0)
	Baloxavir	8.0% (34/424)f	10.8% (26/240)	9.6% (5/52)	1.1% (1/90)	5.6% (2/36)	0% (0/6)
B	NAI	0.5% (1/193)	0% (0/104)	0% (0/48)	2.9% (1/35)	0% (0/4)	0% (0/2)
	Baloxavir	0% (0/44)	0% (0/25)	0% (0/8)	0% (0/7)	0% (0/3)	0% (0/1)

^a(NIID, 2019; Takashita, 2020; Takashita et al., 2020a).

^bAll have an NA-H275Y substitution (N1 numbering).

^cNumber of resistant viruses per total viruses tested.

^d4 patients without prior treatment with NAIs.

^e3 patients shed A(H1N1)pdm09 PA-I38X variants without prior baloxavir treatment.

^f5 patients shed A(H3N2) PA-I38X variants without prior baloxavir treatment.