Evaluating the impact of universal varicella vaccination among preschool-aged children in Qingdao, China: An interrupted time-series analysis

Figures & data

Figure 1. Varicella monthly incidence in Qingdao, China from 2007 to 2020. Solid line depicts smoothing spline in backward moving average with twelve periods in twice. Dashed line depicts the trend of incidence in Qingdao, China from 2007 to 2020. Int1: July 1^st, 2013, the date of free one-dose VarV vaccination. Int2: July 1, 2016, the date of free two-dose VarV vaccination.

Table 1. The incidences and immunization strategies of varicella in Qingdao, China, 2007–2020.

Period	Average Incidence (Per 100,000)	χ^2	P-value	Immunization Schedule
2007~2012	118.76	0.941	0.332	VarV for voluntary self-paying
2013~2015	115.47	358.75	0.000	free one-dose VarV vaccination
2016~2020	60.74			free two-dose VarV vaccination

Note: *P value of χ² test: the average of incidence compared with the next period.

Figure 2. ITS scatter plot of the monthly incidence rate of varicella after adjusted from 2007 to 2020 in Qingdao.Int1: July 1^st, 2013, the date of free one-dose VarV vaccination. Int2: July 1^st, 2016, the date of free two-dose VarV vaccination.

Table 2. Estimated level and trend changes of reported varicella incidence before and after VarV vaccination.

Period	Variables	Coefficient	S.E.	95% CI	DW	P-value
VarV for voluntary self-paying 2007.1–2013.6	Intercept	6.850	0.548	5.705~7.995	0.083	0.000
	Time	0.077	0.011	0.055~0.098		0.000
free one-dose VarV vaccination 2013.7–2016.6	Level change after intervention	−1.637	0.574	−2.762~−0.512		0.005
	Trend changes after intervention	−0.135	0.024	−0.182~−0.088		0.000
free two-dose VarV vaccination 2016.7–2020.12	Level change after intervention	1.189	0.570	0.072~2.306		0.039
	Trend change after intervention	−0.055	0.024	−0.103~−0.008		0.025