Potential impact of B lineage mismatch on trivalent influenza vaccine effectiveness during the 2015–2016 influenza season among nursery school children in Suzhou, China

Figures & data

Table 1. Characteristics of enrolled children aged 3 to 6 years in Suzhou, 2015–2016.

		Vaccinated		Unvaccinated		Total
		N = 1522	%	N = 1756	%	N	%	P
Age(month)	36–47	378	25	492	28	870	27	0.026
	48–59	534	35	545	31	1079	33
	60–72	610	40	719	41	1329	40
Gender	Male	791	52	919	52	1710	52	0.538
	Female	731	48	837	48	1568	48
Preterm birth	Yes	115	8	113	6	228	7	0.208
	No	1407	92	1643	94	3050	93
Medical insurance	Yes	1029	68	1110	63	2139	65	0.008
	No	493	32	646	37	1139	35
Comorbidity^a	Yes	27	2	37	2	64	2	0.492
	No	1495	98	1719	98	3214	98
Respiratory illness in 2 weeks prior to enrolment^b	Yes	500	33	541	31	1041	32	0.210
	No	1022	67	1215	69	2237	68
Residence registration	Suzhou	593	39	678	39	1271	39	0.837
	Other	929	61	1078	61	2007	61
Family income(USdollar/year)^c	<14,706	924	61	1065	61	1989	61	0.831
	14,706–36,765	479	32	544	31	1023	31
	>36,765	119	7	147	8	266	8
Father's Educational background	Under junior middle school	668	44	717	41	1385	42	0.077
	Above junior middle school	854	56	1039	59	1893	58
Mother's Educational background	Under junior middle school	786	52	843	48	1629	50	0.038
	Above junior middle school	736	48	913	52	1649	50

^a Comorbidity includes congenital heart disease, asthma and other chronic lung disease, neuromuscular disease, kidney disease, blood dyscrasia and HIV.

^b Respiratory illness within 2 weeks prior to enrolment includes cold symptoms, bronchitis and pneumonia.

^c 1US$ = 6.80 RMB

Table 2. Incidence of influenza-like illness and relative health care seeking behavior during 6 months follow-up period, Suzhou 2015–16.

		Vaccinated				Unvaccinated
		No children with ILI^c	%	No ILI episodes^d	Incidence (95% CI) per 1,000 person-week	No children with ILI^c	%	No ILI episodes^d	Incidence (95% CI) per 1,000 person-week	p value^e
Influenza-like illness (ILI)^a	Yes	237	16	260	7.2 (6.4–7.9)	296	17	332	8.0 (7.3–8.7)	0.197
Clinical visit due to ILI among those with ILI^b	Yes	85	38	148	4.1 (3.6–4.7)	110	37	213	5.1 (4.6–5.7)	0.034
Hospitalization due to ILI among those with ILI	Yes	14	6	17	0.5 (0.2–0.7)	10	3	10	0.2 (0.1–0.4)	0.093
Purchase medicine due to ILI among those with ILI	Yes	141	59	177	4.9 (4.3–5.5)	144	49	215	5.2 (4.6–5.8)	0.576
Laboratory-confirmed Influenza	Yes	17	1	17	0.5 (0.3–0.7)	23	1	23	0.6 (0.4–0.7)	0.613

^a ILI was defined as axillary temperature ≥38°C, accompanied by cough or sore throat/inflamed pharynx.

^b Clinical visit defined as children who visited a clinic for health services due to ILI symptoms.

^c n stands for number of children with ILI during the follow-up period.

^d n stands for number of episodes; repeat illness report within two weeks was counted as one episode.

^e Mid-P exact test was used to compare two incidence rates.

Table 3. Number of laboratory-confirmed influenza like illnesses and the unadjusted vaccine effectiveness (VE) by sub-type and lineage in the 2015/2016 influenza season in Suzhou.

		Vaccinated	Unvaccinated
		n	n	Risk Ratio (95% CI)	Unadjusted VE^b (95% CI)
Influenza viruses subtype/lineage	B Yamagata^a	0	2	0.57 (0.02–7.50)	43% (−650%,98%)
	B Victoria	12	10	1.37 (0.58–3.27)	−37% (−227%,42%)
	A(H1N1)pdm09	5	11	0.52 (0.16–1.47)	48% (−47%,84%)
	H3N2	0	0	—	—
Any influenza viruse		17	23	0.84 (0.44–1.58)	16% (−58%,56%)

^a We adjusted by adding 0.5 to each cell of the 2 × 2 table that was zero.¹⁹

^b VE was estimated by incidence rate of influenza positives among vaccinated divided by incidence rate of influenza positives among the controls.

Figure 1. Study flowchart: Seasonal influenza vaccine effectiveness study among nursery school children in Suzhou, China, 2015–2106.

Firure 2. Proportion of influenza like illness that was influenza virus positive by sub-type and lineage; data from this study and local surveillance data from outpatient clinics in the Children's Hospital of Soochow University, November 2015 to July 2016.

Mondiale de la Santé, Organisation, World Health Organization. Review of global influenza activity, October 2015-October 2016. Wkly Epidemiol Rec. 2016; 91(51–52):604–22. PMID:27995783.

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