Varicella epidemiology, susceptibility and cost burden in Chongqing China: implications for prevention and control strategies

Abstract

Background

To characterize the epidemiological profile, population seroprotection levels, and economic impact of varicella in Chongqing, and to provide evidence to optimize immunization strategies to reduce incidence and economic burden.

Methods

The epidemiological trends of varicella in Chongqing were ascertained from routine surveillance data (2011–2024). Population sero-epidemiology was evaluated using a randomized cross-sectional serosurvey (n = 960, 2024), and economic burden was estimated from 14,779 outpatient and 298 inpatient cases (2019–2022). Statistical analyses (descriptive statistics, Chi-squared test, Kruskal-Wallis test, and Wilcoxon rank-sum test) were conducted to quantify incidence trends, factors associated with antibody levels, and heterogeneity in economic burden.

Results

A total of 301,714 cases were reported during 2011–2024, with 53.56% in children < 15 years. Incidence exhibited an inverted U-shaped trend. The overall crude varicella IgG seroprevalence was 78.33% (geometric mean concentration, GMC: 351.3 mIU/mL). Notably, children (< 15 years) showed a significant seroprotection gap (seroprevalence: 70.54%; GMC: 240 mIU/mL), which aligned with their disproportionately high incidence. Two-dose vaccination was associated with significantly higher seropositivity (83.50% vs. 66.07%) and GMC (343.7 vs. 189.1 mIU/mL) than one dose (p < 0.01). Adults aged > 50 years exhibited the highest GMC (744.7 mIU/mL) and seropositivity (96.15%), aligning with the lowest incidence recorded in 2024. The pediatric inpatients (< 15 years) had a higher burden ($1375.74 vs. $1012.70, p < 0.01) than individuals over 15 years.

Conclusions

Varicella incidence remains high and children show suboptimal seroprotection against varicella in Chongqing. The disease imposes a substantial financial burden, particularly among pediatric inpatients. It is recommended to expand two-dose varicella vaccine immunization coverage to reduce both incidence and disease burden.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12879-026-13815-4.

Background

Varicella is an acute respiratory infectious disease caused by the Varicella-zoster virus (VZV), which is primarily transmitted via respiratory droplets and direct contact with vesicular fluid. It predominantly affects infants and preschool-aged children and is clinically characterized by the presence of generalized maculopapules, vesicles, and crusts. In severe cases, varicella can lead to complications such as pneumonia and encephalitis, which may pose life-threatening risks [1, 2]. The World Health Organization (WHO) indicated in its 2014 position paper that the global annual disease burden of varicella includes 4.2 million severe complications leading to hospitalization and approximately 4,200 deaths [3], thereby exerting substantial pressure on global public health systems. In China, varicella has consistently been the most frequently reported vaccine-preventable disease among children [4]. Since the varicella vaccine (VarV) has not yet been incorporated into China’s National Immunization Program (NIP), vaccination coverage varies markedly across regions, resulting in the persistent prevalence of the disease [5]. Varicella’s economic burden extends beyond medical resources and social productivity losses. In the United States, the direct medical costs associated with varicella amount to approximately 100 million USD annually, while indirect losses related to unemployment reach 400 million USD [6]. The socioeconomic burden imposed on prevention and control institutions by each case is approximately 5,714 USD, which is 6.7 times greater than the individual socioeconomic burden borne by patients [7]. This underscores the critical importance of varicella prevention and control in mitigating overall societal costs.

Since imported and domestic VarV were successively launched in China in 2000, only a limited number of cities, such as Tianjin and Shanghai, have incorporated a two-dose vaccination schedule into their local immunization programs, while a comprehensive national immunization strategy remains absent [8]. Taking Chongqing as a representative region, a comprehensive analysis was conducted by integrating epidemiological characteristics, population immunity status, and the disease-related economic burden to elucidate the patterns of the epidemic, the current status of seroprotection, and the economic losses. This study aims to provide scientific evidence for improving national varicella immunization strategies in China and offer references for other regions worldwide that have not integrated VarV into their NIP.

Methods

Study subjects and data source

Monthly data from January 1, 2011, to December 30 2024, on varicella incidence in Chongqing were obtained from the National Notifiable Disease Reporting System of China (NNDRS). A retrospective survey was conducted on all the outpatients and inpatients diagnosed with varicella from January 1, 2019, to December 30, 2022, at two municipal hospitals (the two campuses of Children’s Hospital of Chongqing Medical University) and two district/county hospitals (Chongqing No.9 People’s Hospital and the People’s Hospital of Pengshui County). Medical records and expenses of both outpatients and inpatients with a primary diagnosis of varicella were collected through the Hospital Information System (HIS). The economic burden analysis adopted a patient/family perspective. Direct non-medical costs were estimated based on round-trip taxi fares from their residence to the hospital. The fare was set at 1.4 USD for distances less than 3 km, and was calculated as “(distance − 3km) × 0.28 USD/km + 1.4 USD” for distances exceeding 3 km. The indirect costs were estimated using the human capital approach based on the local minimum wage. For pediatric cases (students at schools), indirect costs represent the productivity loss of one parent. For adult cases (who were employed), indirect costs accounted for the patients’ own productivity loss. All costs originally recorded in RMB were converted into USD at a fixed exchange rate of 1 USD ≈ 7.0 RMB for the 2019–2022 study period.

In 2024, a seroepidemiological survey was conducted using a multi-stage stratified random sampling method. The strata were defined by geographic location (urban/rural) and age groups. First, 8 districts/counties were randomly selected from 41 administrative districts and counties of Chongqing to ensure geographic and economic representation. Within each selected district/county, one community/township was randomly selected and participants were recruited through community-based sampling. To handle non-response bias, if a selected individual refused or was unavailable after two contact attempts, the next eligible resident in the same age group was approached until the target sample size (approximately 10 per age group per district) was reached. Inclusion criteria included healthy residents aged ≥ 1 year without acute infectious diseases; individuals with immunodeficiency or recent administration of immunoglobulin/blood products were excluded. Sample size was calculated based on the formula:

where p (61.3%) is the anti-VZV IgG seropositivity among residents of all ages in Youyang County in Chongqing (2019). =1.96, = 0.035 was the maximum allowed error, and deff was the design effect (1.3). The primary sample size calculated was 967. Individual interviews were conducted by trained investigators in order to gather demographic information, and the VarV immunization history for participants ≤ 15 years was sourced and validated through the Chongqing Immunization Planning Information Management System or immunization records kept by the parents, leaving no missing vaccination records among pediatric participants. Participants aged > 15 years with unknown vaccination status were categorized as “unvaccinated” under the assumption of extremely low vaccination coverage in this birth cohort before 2010. The questionnaire used was self-designed for this study (Supplementary file).

The blood samples from each participant were collected after the questionnaire survey. The sera were then separated and transported to the microbiology laboratory of the Chongqing Center for Disease Control and Prevention (CDC) for antibody detection via a commercial enzyme-linked immunosorbent assay (ELISA) kit (Zhengzhou Ete Biotechnology Co., Ltd, Henan Province, China). The Geometric Mean Concentration (GMC) and its 95% confidence intervals (95%CI) were calculated via parametric methods using log-transformed antibody concentrations, with estimates back-transformed to the original scale to correct the right-skewed distribution. Values below the lower quantification limit were imputed with half the limit, and those above the upper assay limit were assigned the upper limit value. Quality control procedures included the use of positive and negative controls in each run. Samples with measured results > 2000 mIU/mL were diluted with diluent and re-tested. Results were interpreted based on the manufacturer’s protocol. A varicella IgG level of ≥ 100 mIU/mL was considered positive, which served as a correlate of protection but did not guarantee complete clinical protection against varicella. Subgroup-specific seroprevalence was calculated and their 95%CIs were estimated using the Wilson score method.

Statistical analysis

The statistical analysis was conducted using R version 4.5.1. Serological data were summarized using GMC with 95% CI, while economic burden data were characterized by the median and interquartile range (IQR). The economic burden data were categorized into < 15 years and ≥ 15 years groups, as medical treatment for adolescents aged over 15 years may differ substantially from that for children, thereby influencing the medical costs. Non-parametric tests were employed to assess subgroup differences. A univariate analysis of factors influencing the seroprevalence was conducted using the Chi-Squared test, with the significance level (α) set at 0.05. To integrate the surveillance, serological, and economic burden components into a unified study framework, we employed a pre-specified descriptive and ecological approach using age as the unifying axis. This framework enabled the parallel examination of age-stratified incidence, seroprevalence/GMC, and economic costs to identify convergent ecological patterns.

Results

Epidemiological characteristics

A total of 301,714 varicella cases were notified in Chongqing during 2011–2024, with an average annual incidence of 69.74 per 100,000 population, with 2 reported mortalities in 2013. The incidence slightly increased from 2011 (21.25 per 100,000) to 2019, with an average annual growth rate of 26.93%, peaking at 133.85 per 100,000 population in 2019. Subsequently, it decreased from 83.51 per 100,000 in 2020 and 67.30 per 100,000 in 2024, at an average annual decline rate of 4.76% (Fig. 1). The age distribution predominantly comprised children under 15 years, accounting for 53.56% of cases, while individuals aged 15 years and older constituted 46.44% of cases.

Fig. 1.

Annual reported varicella cases and incidence in Chongqing, 2011–2024. The left Y-axis represents incidence per 100,000 population (green line), and the right Y-axis represents the number of cases (blue bars). The figure illustrates the peak in 2019 followed by a gradual decline

Seroprevalence of varicella IgG

A total of 960 participants were enrolled, with approximately 80 individuals in each group (ten from each district/county). Age strata were defined as: 1–6 years (single year groups), 7–14 years, 15–19 years, 20–29 years, 30–39 years, 40–49 years, and ≥ 50 years. The male-to-female ratio was 0.77:1. Overall, 560 individuals (58.33%) were aged < 15 years. Only 206 participants (21.46%) had received two doses of VarV.

The overall crude anti-VZV IgG seropositivity was 78.33% (752/960), with a GMC of 351.3 mIU/mL. Notably, participants aged ≥ 15 years had significantly higher seropositivity (89.25%) and GMC (590.2 mIU/mL) than children aged < 15 years (70.54% and 240 mIU/mL, respectively). Individuals who received two doses of varicella vaccine exhibited significantly higher seropositivity (83.50%) and GMC (343.7 mIU/mL) compared to those who received only one dose (66.07% and 189.1 mIU/mL, respectively; p < 0.01). However, the overall GMC in the unvaccinated population (511.1 mIU/mL) was higher than that in both the one-dose and two-dose groups, although their seropositivity (83.33%) was comparable to that of the two-dose group.

Among children aged 1–2 years, unvaccinated participants had a seropositivity of 50.0% (GMC: 125.1 mIU/mL), which was significantly lower than age-matched children who received one dose (79.34% and 251.9 mIU/mL). However, in the 3–5 years age group, the seropositivity of unvaccinated individuals (58.82%) was comparable to that of the one-dose group (57.63%) and lower than the two dose group (87.74%), yet the GMC among unvaccinated children (340.7 mIU/mL) was notably higher than that of the one-dose group (148.2 mIU/mL). In contrast, adults (19–49 years and > 50 years) exhibited high seropositivity (92.06% and 96.15%) and high GMCs. (Table 1).

Table 1.

Distribution of varicella virus IgG levels in serological survey of Chongqing in 2024

Subgroups		Number of subjects (n, %)	GMC (95%CI, mIU/mL)	P	Seropositivity(95%CI, %)	P
Gender				0.56		0.23
Male		417(43.44)	328.5(282.9-381.4)		76.50(72.2-80.32)
Female		543(56.56%)	369.7(329.8-414.4)		79.74(76.16-82.91)
Age	Immunization
1–2 years	Unvaccinated	38(23.75)	125.1(73.5-212.9)	< 0.01	50.0(34.85–65.15)	< 0.01*
	One dose	121(75.63)	251.9(199.2-318.4)		79.34(71.28–85.60)
	Two doses	1(0.63)	331.0		100(-)
3–5 years	Unvaccinated	17(7.05)	340.7(148.1-783.6)	< 0.01	58.82(36.01–78.39)	< 0.01
	One dose	118(48.96)	148.2(113.9-192.8)		57.63(48.61–66.16)
	Two doses	106(43.98)	435.4(312.0-607.7)		87.74(80.14–92.69)
6–18 years	Unvaccinated	89(38.86)	372.4(263.2-526.7)	< 0.01	66.29(55.98–75.26)	< 0.01
	One dose	41(17.90)	153.4(82.9-283.8)		51.22(36.48–65.75)
	Two doses	99(43.23)	268.2(206.8-347.8)		78.79(69.74–85.69)
19–49 years	Unvaccinated	252(100)	621.6(552.4-699.5)	-	92.06(88.06–94.80)	-
> 50 years	Unvaccinated	78(100)	744.7(626.7–885.0)	-	96.15(89.29–98.68)	-
Immunization				< 0.01		< 0.01
Unvaccinated		474(49.37)	511.1(457.4-571.1)		83.33(79.71–86.42)
One dose		280(29.17)	189.1(159.2-224.7)		66.07(60.34–71.37)
Two doses		206(21.46)	343.7(277.9-425.1)		83.50(77.82–87.94)
Total		960	351.3(320.6-384.9)		78.33(75.62–80.82)

Kruskal-Wallis (KW) test was used for comparing differences among multiple groups. Wilcoxon rank sum test was conducted for comparing differences between two groups

^* The only one child with two doses was combined with one dose to conduct Wilcoxon rank sum test

Varicella economic burdens

Medical expenses data were collected from 14,779 outpatient cases and 298 inpatient cases. Among the outpatient cases, 8,052 (54.48%) were male and 6,727 (45.52%) were female, with 13,978 (94.58%) aged < 15 years. The median total economic burden for inpatients was significantly higher than that for outpatients. For outpatient cases, the total economic burden for individuals aged ≥ 15 years was 54.36 USD, which exceeded that of individuals < 15 years (36.16 USD). Conversely, pediatric inpatients (< 15 years) had a median economic burden of 1,375.74 USD, which was higher than the 1,012.70 USD seen in patients aged ≥ 15 years. Statistically significant differences in total economic burden were observed across different hospital levels (p < 0.01, Tables 2 and 3). However, the absolute median difference in both the medical expenses and economic burdens between genders was negligible for outpatients, this statistical significance is driven by a large sample size rather than a meaningful practical difference.

Table 2.

Economic burden of outpatient varicella cases in Chongqing from 2019 to 2022 (Median, Interquartile Range)

Group	Direct medical expenses (USD)	P	Direct non-medical expenses (USD)	P	Indirect economic burden (USD)	P	Total economic burden (USD)	P
Gender		<0.01		<0.05		<0.05		<0.01
Male	11.07(5.95–15.95)		12.81(9.15–15.67)		13.86(9.84–25.43)		36.82(29.30–47.30)
Female	11.10(5.96–15.50)		12.60(9.15–15.03)		13.68(9.64–25.43)		36.45(29.30-45.33)
Age		<0.01		<0.01		<0.05		<0.01
<15 years old	11.00(5.95–15.02)		12.81(9.15–15.26)		13.86(9.84–25.43)		36.16(29.30–45.00)
≥ 15 years old	24.14(8.03–51.80)		11.48(8.57–18.89)		16.10(8.98–25.43)		54.36(35.79–77.76)
Region		<0.01		<0.01		<0.01		<0.01
Municipal hospitals	10.73(5.77–13.97)		14.09(9.15–15.93)		14.96(10.62–25.43)		35.78(29.30-43.63)
District/county hospitals	24.86(9.49–43.41)		8.93(7.99–12.67)		10.15(7.77–22.80)		46.67(30.39–66.29)
Total	10.09(5.95–15.70)		12.74(9.15–15.26)		13.86(9.84–25.43)		36.63(29.30-46.29)

Wilcoxon rank-sum test was used for comparing differences between two groups

Table 3.

Economic burden of inpatient varicella cases in Chongqing from 2019 to 2022 (Median, Interquartile Range)

Group	Direct medical expenses (USD)	P	Direct non-medical expenses (USD)	P	Indirect economic burden (USD)	P	Total economic burden (USD)	P
Gender		0.81		0.19		0.07		<0.01
Male	837.25(572.86-1710.38)		84.91(50.10-167.62)		213.41(158.02-332.37)		1230.80(824.46-2362.04)
Female	911.91(619.71-1704.82)		71.85(49.28–133.00)		204.98(162.26–262.80)		1241.98(876.85-2266.72)
Age		<0.01		<0.01		<0.05		<0.01
<15 years old	1013.22(652.73-1961.50)		80.08(48.38-149.11)		201.84(151.70-270.70)		1375.74(884.80-2450.31)
≥ 15 years old	620.39(455.99-946.25)		63.61(52.51-134.25)		223.70(188.80-352.31)		1012.70(731.54-1718.26)
Region		<0.01		<0.01		0.08		<0.01
Municipal hospitals	855.19(612.54-1664.18)		82.56(49.65-149.62)		205.29(157.57-275.58)		1164.63(838.19-2113.30)
District/county hospitals	572.18(434.55-759.26)		63.52(48.86–137.60)		219.15(169.49-352.69)		952.94(677.76-1591.38)
Total	880.56(597.88-1696.85)		79.20(49.69-149.14)		209.97(159.56-292.91)		1237.26(842.02-2286.63)

Wilcoxon rank-sum test was used for comparing differences between two groups

Integrated age-dependent profile of incidence and seropositivity

Reported incidence in 2024 exhibited an inverted U-shaped trend, peaking in the 6–18 years age group. In contrast, serological markers demonstrated a continuous increase with age. Specifically, the 6–18 years group, which bore the highest disease burden, showed suboptimal seroprotection with a seropositivity considerably lower than that of adults. Conversely, the adult groups (≥ 19 years) presented a divergent ecological pattern where higher seropositivity coincided with lower incidence: individuals aged > 50 years exhibited the highest GMC (744.7 mIU/mL) and seropositivity (96.15%), which ecologically aligned with the lowest incidence in 2024 (Fig. 2).

Fig. 2.

Age-stratified comparison of varicella IgG antibody levels and reported incidence in Chongqing, 2024. The left Y-axis represents the geometric mean concentration (GMC) of IgG (the green stacked segment), and reported incidence (dark blue line) with numeric annotations (per 100,000 population); and the right Y-axis represents the investigated seropositivity (blue bars) with numeric annotations (%)

Discussion

The seropositivity of varicella virus IgG among children under 15 years was 70.54%, surpassing the seroprevalence of 65.59% observed in children aged 1–14 years in Hangzhou [9], and 54.4% among kindergarten children aged 4–6 years in Suzhou [10]. These findings reflect insufficient population immunity among children in China, which can be attributed to the non-NIP characteristic of the VarV and the pronounced regional disparities in vaccination coverage [11, 12]. Research from the Asia-Pacific region corroborates that countries and regions not incorporating the vaccine into their NIP generally experience low vaccination coverage [13].

Age was identified as a critical determinant of antibody levels; the seroprevalence and GMC among individuals aged ≥ 15 years were significantly higher than those in children aged < 15 years. This further substantiates the notion that most VZV infections occur during childhood, with the prevalence reaching up to 95% in adulthood, as evidenced by studies conducted in France [14]. The seropositivity among individuals aged > 50 years was observed to be 96.15%, underscoring the important role of natural atypical infection in inducing seroprotection in adults. This finding aligns with the 92% seropositivity for protective antibodies reported among Brazilian adults lacking a clinical varicella history [15]. Notably, the observed trend of increasing antibody levels with advancing age in Chongqing parallels the serological research outcomes from South Korea, Europe, and other regions [16, 17], suggesting that the age-dependent cumulative effect of seroprotection is universally applicable.

The WHO has stated that “the two-dose vaccination schedule is more effective” in a position paper [3]. Individuals who received two doses of VarV exhibited significantly higher seropositivity and GMC compared to those with only one dose, reinforcing the superior immunogenicity and effectiveness of the two-dose schedule. Similarly, a Suzhou study found higher seroprevalence (96.85%) in children with two VarV doses than in those with one dose (94.56%) or unvaccinated (88.50%) [18]. Our observation that the overall GMC and seropositivity in the unvaccinated group were higher than those in the one-dose group is consistent with an Argentina investigation [19]. It may be attributed to lower antibody persistence following a single vaccine dose over time, or potentially due to insufficient primary immunization. In the youngest cohort (1–2 years), while unvaccinated children had significantly lower seropositivity and GMC compared to their one-dose vaccinated counterparts, this confirms that the vaccination provides a clear immunological advantage.

Conversely, the higher GMC observed among unvaccinated individuals aged 3–5 years and the overall high seroprevalence in unvaccinated adults likely reflect the cumulative effect of natural infection with wild-type VZV, which generally induces higher and more durable antibody levels than a single vaccine dose. The lower GMC in the children aged 3–5 years with one-dose immunization group versus unvaccinated seropositive counterparts indicates early antibody waning following a single dose, unlike the stronger response from natural infection. The cross-sectional design without longitudinal data cannot robustly distinguish between vaccine-induced and naturally acquired immunity, nor the primary vaccine failure from waning antibodies. Nevertheless, the stratified analysis suggests that the suboptimal protection from a single dose stem from a combined effect of primary vaccine failure, antibody waning, and community wild-type virus exposure. Additionally, the disease burden associated with natural infection is substantially higher than the cost of vaccination. This highlights the necessity of a two-dose vaccination schedule to ensure long-term seroprotection.

Varicella imposes a substantial economic burden on the families of patients. The per capita direct hospitalization cost (880.56 USD) surpasses the economic burden reported for varicella inpatients in Qingyang City, which was 487 USD [20]. Such regional disparities may be attributed to variations in price levels, medical insurance policies, healthcare-seeking behaviors, and hospital charging standards. The per capita total economic burden for outpatient cases was found to be lower than the average level in European countries [21]. The hospitalization costs were higher in municipal hospitals compared to district or county hospitals. There are superior medical services, advanced diagnostic capabilities, and treatment technologies available in municipal hospitals. Thus, the hospitals can handle more severe or complex cases with higher treatment costs, leading to higher medical expenditures for severe cases and imposing a greater financial burden on families and society [7]. International research indicates that the economic burden associated with varicella varies considerably across countries with different income levels. Nevertheless, middle- and high-income countries generally bear high costs associated with varicella outpatient and inpatient care, with the actual burden often underestimated [21]. In China, the underreporting for varicella is approximately 71% [22], implying that the actual disease burden of varicella in Chongqing may be far higher than the current observed burden. The economic burden associated with outpatient cases aged ≥ 15 years was greater. This disparity may be attributed to the fact that medication costs for adults are typically higher than those for pediatric patients. A systematic review conducted in the Asia-Pacific region indicated that children are the major population affected by varicella morbidity and hospitalization, the integration of VarV into the NIP can significantly reduce hospitalization among children [13].

Specifically, children aged < 15 years exhibit a low seroprevalence (70.54%) and constitute a high-risk group for varicella [23, 24]. Their hospitalization costs (1375.74 USD) are notably higher than those for adults, which ecologically aligns with a pattern of “high susceptibility - high incidence - high burden” in this age group. This suboptimal seroprotection in children correlates with a higher disease burden, which highlights children as the priority population for targeted vaccination interventions. Despite relatively high antibody levels among adults, 5%-10% remain susceptible to varicella, and adult cases tend to present with more severe symptoms and a higher risk of complications [25, 26]. A comprehensive study examining the trend of varicella-zoster disease burden in China from 1990 to 2021 demonstrated that while the morbidity remains stable and mortality is declining, the risk remains elevated for females and the elderly. Consequently, the disease burden is projected to continue posing a public health challenge by 2030 [27].

In summary, to reduce the incidence and severity of varicella, as well as to mitigate the strain on medical resources and associated socioeconomic losses, it is essential to establish and optimize a comprehensive prevention and control system. Such strategies include promoting equitable global vaccination coverage and improving vaccine accessibility; lowering barriers to immunization through policy support, such as medical insurance inclusion and free vaccination programs; expanding serological surveillance to dynamically delineate the distribution of susceptible populations; implementing routine morning and afternoon screening protocols and timely case isolation in key settings such as schools and kindergartens to mitigate outbreaks; strengthening protection for high-risk groups including healthcare workers; and standardizing clinical diagnosis and treatment practices to curtail unnecessary medical expenditures and effectively alleviate the economic burden on patients.

The study also has limitations: the serosurvey utilized an equal allocation sampling strategy rather than proportional allocation, the reported overall seroprevalence is an unweighted estimate. Secondly, a cross-sectional design cannot track changes in antibody levels over time, precluding the ability to robustly distinguish between vaccine-induced immunity and naturally acquired immunity, or to differentiate primary vaccine failure from waning immunity. Thirdly, the economic burden assessment likely underestimates the true societal burden, as direct non-medical costs were restricted to taxi fares and indirect costs omitted caregiver time, productivity losses beyond treatment encounters, and intangible costs. Finally, the relationship among vaccination, seroprevalence, and disease burden was not quantitatively analyzed, which requires further cohort studies. Future research should integrate vaccination data for modelling analysis of vaccination impact on immunity and disease burden.

Conclusions

Children in the city of Chongqing show suboptimal varicella seroprotection, with an evident age‑related seroprevalence gap and substantial economic burden. Two‑dose vaccination is necessary, along with comprehensive strategies including enhanced surveillance and expanded immunization to reduce susceptibility and disease burden.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary Material 1 ^{(14.6KB, docx)}

Abbreviations

VZV

Varicella-zoster Virus

WHO

World Health Organization

VarV

Varicella vaccine

NIP

National Immunization Program

NNDRS

National Notifiable Disease Reporting System

HIS

Hospital Information System

CDC

Center for Disease Control and Prevention

ELISA

Enzyme-linked immunosorbent assay

GMC

Geometric Mean Concentration

CI

Confidence intervals

IQR

Interquartile range

Author contributions

YL, HQ.J, and SS.K conceptualized the study design. JW.X, HZ, and CB.Z were in charge of data acquisition (field or laboratory). YL and JY.D were involved in results interpretation and visualization. NY, JY.D, and SS.K drafted the manuscript. JW.X and CB.Z critically revised the manuscript. All authors provided critical feedback and helped shape the research, analysis and approved the final manuscript.

Funding

None.

Data availability

The datasets used in the study are available from the authors on reasonable request.

Declarations

Ethical approval

All the information on the mandatory reported varicella cases is extracted from the network of the National Mandatory Disease Reporting System (NNDRS). All procedures involving research study participants in the serological survey were conducted in accordance with the principles of the Helsinki Declaration and approved by the Ethical Committee of Chongqing CDC (NO.:2024-KY-034-1). Written informed consents were obtained from all participants or their parents/legal guardians prior to enrolment.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.