Changes in epidemiological characteristics and sero-prevalence against the varicella zoster virus in school-age children after the introduction of a national immunization program in Japan

Figures & data

Table 1. Number of students

	2007 group	2008 group	2017 group
Number of students*	137/144	142/144	249/252
Male:Female	91:46/96:48	95:47/96:48	160:89/162:90
Vaccination at admission
None	37	51	19
Single dose	97	89	151
Two doses	3	2	78
Three doses	0	0	1

*: The number of students enrolled in the present study/Number of students at the year of admission

Figure 1. History of varicella infection before admission to elementary school in students who received varicella vaccination and those who did not. Total number were 279 in 2007–2008, and 249 in 2017. The number of students with a history of varicella decreased from 114 (41%) in 2007–2008 to 48 (19%) in 2017. Six students had a history of varicella within six weeks after varicella vaccination were defined as unknown

Statistical significance (p < .01) is shown (*).

Figure 2. The mean age of students with natural infection and breakthrough varicella

Two students in 2017 for whom age of varicella infection was not obtained were excluded from the analysis. Error bar shows 95% CI. Statistical significance (p < .05) is shown (*): * P < .05, ** P < .01.

Table 2. Vaccine effectiveness pre- and post- introduction of national immunization program

(A) 2007–2008
	History of varicella			Prevalence ratio
Vaccination	+	-	Prevalence of varicella	(95%CI)	P value
None	68	22	0.76	Reference	Reference
Single dose	43	139	0.24	0.313 (0.235–0.416)	0.000
Two doses	1	4	0.2	0.265 (0.046–1.534)	0.019
(B) 2017
None	14	5	0.74	Reference	Reference
Single dose	28	119	0.19	0.259 (0.168–0.397)	0.000
Two doses	2	76	0.025	0.035 (0.009–0.140)	0.000

Table 3. Positivity for anti-VZV IgG antibodies and vaccination doses

(A) 2007–2008
Vaccination	History of varicella	N	Students with positive antibodies	Positive rates (%)	95%CI (%)
No vaccination	+	66	66	100	95–100
	-	22	12	55	32–76
Single dose	+	43	40	93	81–99
	-	139	69	50	41–58
Two doses	+	1	1	100	3–100
	-	4	4	100	40–100
(B) 2017
No vaccination	+	10	10	100	69–100
	-	5	0	0	0–52
Single dose	+	28	22	79	59–92
	-	119	34	29	21–38
Two doses	+	2	2	100	16–100
	-	76	33	43	32–55

Figure 3. Varicella infection after admission to elementary school in students without BV who received a single dose of varicella vaccine at admission