Low population serum microneutralization antibody titer against the predominating influenza A(H3N2) N121K virus during the severe influenza summer peak of Hong Kong in 2017

Figures & data

Fig. 1 Total number and percentage of influenza A(H3) virus detected in Hong Kong from 2014 to 2017.

The data were obtained from the Public Health Laboratory Services of Hong Kong³⁹

Major amino acid substitutions of A(H3N2) viruses from Hong Kong. Amino acid sequence data were downloaded from Global Initiative on Sharing All Influenza Data (GISAID) EpiFlu database (Supplementary Table 1)

HA amino acid substitution	2014–2015 (n = 51)	2016 (n = 13)	2017^a (n = 189)
N121K	0 (0%)	1 (7.7%)	99 (52.4%)
T135K	0 (0%)	0 (0%)	55 (29.1%)
S144K	0 (0%)	0 (0%)	37 (19.6%)

^a Up to 13 December 2017

Fig. 2 Phylogenetic trees showing the relationship between influenza A(H3N2) viruses from Hong Kong in 2017, other representative A(H3N2) viruses, and recommended A(H3N2) viruses for influenza vaccines^{12, 13}.

The phylogenetic tree was constructed using the Maximum Likelihood method based on the Hasegawa–Kishino–Yano model. All sequences were obtained from the Global Initiative on Sharing All Influenza Data (GISAID) Database (Supplementary Table S1)

Microneutralization and hemagglutination inhibition titer against the 2017 H3N2 circulating strain (3391/2017) and the 2016/17 influenza vaccine A(H3N2) strain (4801/2014)

	Hospital patient (n = 435)		P-value	Vaccinees (n = 200)		P-value
Median age (IQR)	66 (43–78)			56 (45–64)
Virus strain	3391/2017^a	4801/2014^b		3391/2017^a	4801/2014^b
GMT
MN (95% CI)	13.4 (12.1–14.9)	47.8 (40.6–56.3)	<0.0001	23.1 (18.8–28.2)	125.1 (99.0–158.1)	<0.0001
HI (95% CI)	96.9 (87.0–107.8)	55.4 (50.1–61.2)	<0.0001	276.7 (232.7–329.0)	166.2 (140.7–196.3)	<0.0001
% of individuals with antibody titer ≥40
MN titer ≥40, No. (%)	115 (26.4)	261 (60.0)	<0.0001	86 (43.0)	164 (82.0)	<0.0001
HI titer ≥40, No. (%)	384 (88.3)	318 (73.1)	<0.0001	191 (95.5)	186 (93.0)	NS

CI confidence interval, GMT geometric mean titer, HI hemagglutination inhibition, IQR interquartile range, MN microneutralization, NS not significant

^a 3391/2017 = A/Hong Kong/3391/2017 A(H3N2) (2017 circulating strain; 121K/144K)

^b 4801/2014 = A/Hong Kong/4801/2014 A(H3N2) (2016/2017 and 2017/2018 vaccine strain; 121N, 144S)

Comparison of microneutralization and hemagglutination inhibition titers between 3391/2017 and 4801/2014

Antibody titer against 3391/2017^a at least fourfold lower than that against 4801/2014^b	Hospital patients	Vaccinees
MN titer, No. (%)	257 (59.1%)	142 (71%)
HI titer, No. (%)	0 (0%)	3 (1.5%)

HI hemagglutination inhibition, MN microneutralization

^a 3391/2017 = A/Hong Kong/3391/2017 A(H3N2) (2017 circulating strain; 121K/144K)

^b 4801/2014 = A/Hong Kong/4801/2014 A(H3N2) (2016/2017 and 2017/2018 vaccine strain; 121N, 144S)

Microneutralization and hemagglutination inhibition titers stratified by age group

Age group	Hospital patient
	MN titer		P-value^b	HI titer		P-value^b
	3391/2017	4801/2014		3391/2017	4801/2014
18–64 years (n = 186)	8.9 (7.8–10.1)	21.2 (15.43–23.13)	<0.0001	74.5 (65.0–85.5)	48.4 (42.2–55.5)	<0.0001
65 years or above (n = 249)	18.2 (15.7–21.2)	87.9 (61.43–92.17)	<0.0001	117.8 (101.1–137.3)	61.2 (53.2–70.5)	<0.0001
P-value^a	<0.0001	<0.0001		<0.0001	0.07

	Vaccinees
	MN titer		P-value^b	HI titer		P-value^b
	3391/2017	4801/2014		3391/2017	4801/2014
18–64 years (n = 154)	27.3 (21.4–34.8)	136.7 (104.3–179.1)	<0.0001	287.2 (234.1–352.5)	175.1 (144.2–211.5)	<0.0001
65 years or above (n = 46)	13.1 (9.8–17.5)	93.0 (58.0–149.3)	<0.0001	244.0 (176.6–337.1)	139.7 (100.5–194.2)	<0.0001
P-value^a	0.012	0.051		0.088	0.113

^a 18–64 age group vs 65 or above age group

^b 3391/2017 vs 4801/2014

Centre for Health Protection. Statistics on Laboratory Surveillance. Influenza virus subtyping. Available at https://www.chp.gov.hk/en/statistics/data/10/641/643/2275.html. Accessed on 18 December 2017.

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