The impact of varicella vaccination: A 2005–2019 interrupted time series analysis

Figures & data

Figure 1. Varicella hospital discharges at hospital del Niño (2005–2019).

Table 1. Characteristics of patients hospitalized with varicella in the hospital del Niño Dr José Renán Esquivel (2005–2019).

	Pre-vaccination period	Transition period	Post-vaccination period
	(2005–2011) N = 145	(2012–2014) N = 80	(2015–2019) N = 68
Gender
Male	92 (63.4%)	50 (62.5%)	37 (54.4%)
Female	53 (36.6%)	30 (37.5%)	31 (45.6%)
Age group
<1 year	54 (37.2%)	30 (37.5%)	33 (48.5%)
1–4 years	69 (47.6%)	36 (45.0%)	20 (29.4%)
5–9 years	17 (11.7%)	10 (12.5%)	8 (11.8%)
10–14 years	5 (3.4%)	4 (5.0%)	7 (10.3%)
Complications
<1 year	27 (18.6%)	17 (21.3%)	19 (27.9%)
1–4 years	43 (29.7%)	27 (33.8%)	14 (20.6%)
5–9 years	9 (6.2%)	7 (8.8%)	5 (7.4%)
10–14 years	2 (1.4%)	1 (1.3%)	3 (4.4%)
Deaths
<1 year	2 (1.4%)	0 (0.0%)	2 (2.9%)
1–4 years	1 (0.7%)	1 (1.3%)	2 (2.9%)
5–9 years	1 (0.7%)	1 (1.3%)	0 (0.0%)
10–14 years	1 (0.7%)	0 (0.0%)	0 (0.0%)
Vaccination status
<1 year	NA	0 (0.0%)	0 (0.0%)
1–4 years	NA	2 (2.5%)	0 (0.0%)
5–9 years	NA	0 (0.0%)	0 (0.0%)
10–14 years	NA	0 (0.0%)	0 (0.0%)
Hospitalization length (median days)
<1 year	5.0	4.5	6.0
1–4 years	4.0	4.5	5.0
5–9 years	3.0	4.0	6.0
10–14 years	3.0	4.0	25.0

*Source: Health Records and Statistics Area from Hospital del Niño Dr. José Renán Esquivel.

**Data corresponds to the 293 clinical records evaluated.

Table 2. Distribution of complications due to varicella by age group in the hospital del Niño Dr José Renán Esquivel patients (2005–2019).

	Pre-vaccination period (2005–2011)				Total	Transition period (2012–2014)				Total	Post-vaccination period (2015–2019)				Total
Age group (years)	<1 year N = 54	1–4 years N = 69	5–9 years N = 17	10–14 years N = 5	145	<1 year N = 30	1–4 years N = 36	5–9 years N = 10	10–14 years N = 4	80	<1 year N = 33	1–4 years N = 20	5–9 years N = 8	10–14 years N = 7	68
TYPE OF COMPLICATION
Skin and soft tissue infection	26 (48.1%)	41 (59.4%)	6 (35.2%)	1 (20.0%)	74 (51.0%)	14 (46.6%)	26 (72.2%)	7 (70.0%)	0 (0.0%)	47 (58.7%)	12 (36.3%)	13 (65.0%)	5 (62.5%)	1 (14.2%)	31 (45.5%)
Pneumonia secondary to varicella	0 (0.0%)	1 (1.4%)	0 (0.0%)	0 (0.0%)	1 (0.68%)	0 (0.0%)	0 (0.0%)	1 (10.0%)	0 (0.0%)	1 (1.2%)	4 (12.1%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	4 (5.8%)
Febrile seizure	1 (1.8%)	2 (2.8%)	0 (0.0%)	0 (0.0%)	3 (2.0%)	0 (0.0%)	1 (2.7%)	0 (0.0%)	0 (0.0%)	1 (1.2%)	1 (3.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1 (1.4%)
Varicella encephalitis	0 (0.0%)	0 (0.0%)	1 (5.8%)	0 (0.0%)	1 (0.68%)	0 (0.0%)	1 (2.7%)	0 (0.0%)	0 (0.0%)	1 (1.2%)	1 (3.0%)	2 (10.0%)	0 (0.0%)	0 (0.0%)	3 (4.4%)
Post-varicella cerebellar ataxia	0 (0.0%)	1 (1.4%)	0 (0.0%)	0 (0.0%)	1 (0.68%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)
Facial paralysis secondary to varicella	0 (0.0%)	0 (0.0%)	1 (5.8%)	0 (0.0%)	1 (0.68%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)
Acute post-infectious glomerulonephritis (post-varicella)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1 (25.0%)	1 (1.2%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)
Aseptic meningitis	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1 (3.3%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1 (1.2%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)
Post-varicella Guillain Barré syndrome	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1 (14.2%)	1 (1.4%)
Septic shock	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1 (14.2%)	1 (1.4%)

*Source: Health Records and Statistics Area from Hospital del Niño Dr. José Renán Esquivel.

**Data corresponds to the 293 clinical records evaluated. Complications are counted per occurrence. One patient may have had several complications.

Figure 2. Age distribution of varicella hospital discharges at hospital del Niño (2005–2019).

Figure 3. Observed vs. expected varicella hospital discharges in children under 14 years of age.

Table 3. Estimated level and trend changes of reported varicella incidence before and after vaccine introduction by age group.

Age Group	Period	Parameter	Coefficient	Standard Error	t	p value	95% CI
Children 0–14 years of age
	Pre-vaccination	β0 2005	22.39	3.67	6.09	.00	14.31	30.48
		β1Tt (slope)	5.39	1.85	2.91	.01	1.31	9.47
	Post-vaccination	β2 (level change)	−13.63	13.24	−1.03	.33	−42.78	15.52
		β3 (intervention effect)	−6.43	1.77	−3.62	.00	−10.34	−2.52
Children 1–4 years of age
	Pre-vaccination	β0 2005	14.20	2.09	6.81	.00	9.61	18.79
		β1Tt (slope)	1.71	1.19	1.44	.18	−0.90	4.33
	Post-vaccination	β2 (level change)	10.86	2.24	4.85	.00	5.93	15.78
		β3 (intervention effect)	−3.09	0.91	−3.38	.01	−5.10	−1.08
Children 5–9 years of age
	Pre-vaccination	β0 2005	7.40	3.69	2.00	.07	−0.73	15.53
		β1Tt (slope)	1.04	0.58	1.79	.10	−0.24	2.31
	Post-vaccination	β2 (level change)	5.04	2.68	1.88	.09	−0.85	10.93
		β3 (intervention effect)	−1.45	0.65	−2.24	.05	−2.88	−0.02

β0 represented the number of varicella cases at the hospital in 2005.

β1 was the slope of varicella cases during the pre-vaccination period.

β2 was the change in the level after vaccine introduction.

β3 represented the differences between the pre-vaccination and the post-vaccination slopes.

Figure 4. Observed vs. expected varicella hospital discharges in children 1–4 years of age.

Figure 5. Observed vs. expected varicella hospital discharges in children 5–9 years of age.

Data availability statement

The data supporting this study’s findings are available from the corresponding author DE upon reasonable request.