Varicella outbreak in a highly-vaccinated school population in Beijing, China during the voluntary two-dose era

Varicella outbreak at nursery school under routine immunization in Japan in 2017 and 2018 and vaccine effectiveness

BACKGROUND

In Japan, routine administration to one-year-old children of two-dose immunization for varicella was introduced in October 2014. Object The object of this study was to report outbreaks of varicella under routine immunization at a nursery school and in its surrounding area using data of surrounding areas from the (Nursery) School Absenteeism Surveillance System. Then, we measured the effectiveness of routine two-dose immunization for varicella to onset. We tentatively assessed its severity in a nursery school.

METHOD

The study period extended from April 2017 through March 2018. The study area comprised Nursery school B and other nursery schools, and elementary and junior high schools in City A. Subjects in Nursery school B were 120 children. We analyzed vaccine effectiveness (VE) as an observational study and assessed severity using Fisher's exact test. We also assessed VE for severity using linear regression. Severity was defined as the length of nursery school absence attributable to varicella infection.

RESULTS

During the one month preceding a period of two weeks before the initial case at Nursery school B, there were 16 cases of varicella infection in nursery schools, 45 cases in elementary schools, and one case in junior high schools in City A. For children who had received one vaccine dose or more, VE was 48.1% for all ages and 49.2% among children three years old and older. No significant VE against infection was found. Vaccination using one dose or more can reduce severity significantly.

DISCUSSION AND CONCLUSION

Because many nursery school children who had received two doses of vaccine were infected, VE was estimated as low in the nursery school and not significant. Although VE for severity with more than one dose was confirmed, a second dose might not reduce severity compared to one dose.

The epidemiology of varicella and effectiveness of varicella vaccine in Ganyu, China: a long-term community surveillance study

BACKGROUND

The real-world data of long-term protection under moderate vaccination coverage is limited. This study aimed to evaluate varicella epidemiology and the long-term effectiveness under moderate coverage levels in Ganyu District, Lianyungang City, Jiangsu Province.

METHODS

This was a population-based, retrospective birth cohort study based on the immunization information system (IIS) and the National Notifiable Disease Surveillance System (NNDSS) in Ganyu District. Varicella cases reported from 2009 to 2020 were included to describe the epidemiology of varicella, and eleven-year consecutive birth cohorts (2008-2018) were included to estimate the vaccine effectiveness (VE) of varicella by Cox regression analysis.

RESULTS

A total of 155,232 native children and 3,251 varicella cases were included. The vaccination coverage was moderate with 37.1%, correspondingly, the annual incidence of varicella infection increased 4.4-fold from 2009 to 2020. A shift of the varicella cases to older age groups was observed, with the peak proportion of cases shifting from 5-6 year-old to 7-8 year-old. The adjusted effectiveness of one dose of vaccine waned over time, and the adjusted VE decreased from 72.9% to 41.8% in the one-dose group.

CONCLUSIONS

The insufficient vaccination coverage (37.1%) may have contributed in part to the rising annual incidence of varicella infection, and a shift of varicella cases to older age groups occurred. The effectiveness of one dose of varicella vaccine was moderate and waned over time. It is urgent to increase varicella vaccine coverage to 80% to reduce the incidence of varicella and prevent any potential shift in the age at infection in China.

Explore the optimal timing for administering the second dose of the varicella vaccine in China

The prevalence of varicella in China has been increasing annually, with a relatively high incidence rate of breakthrough cases. Administering two doses of the varicella vaccine (Varv) proves to be the most effective measure. The objective of this study is to assess the immunogenicity of two doses of the Varv at varying intervals and explore the optimal timing for administering the second dose of the Varv. Utilizing a prospective cohort study design, the quantification of varicella immunoglobulin G (IgG) antibodies' geometric mean concentrations (GMC) is conducted through glycoprotein-based enzyme-linked immunosorbent assay (gpELISA). A total of 903 infants were included in the per-protocol population. After completing the first dose of the Varv, the GMC of antibody after 1 month (Group A) was 463.8 (447.6-480.1) mIU/mL. There was a statistically significant difference in GMC and seroconversion rates among the groups (B/C/D) that received the second dose of the Varv (p < 0.05). Multiple comparisons revealed that the group with a 3-year interval between the two vaccine doses had a higher GMC of 665.2 (622.6-707.8) mIU/mL compared to the group with a 1-year interval of 611.1 (577.1-645.3) mIU/mL and the group with a 5-year interval of 564.7 (540.1-589.4) mIU/mL. To effectively prevent and control the varicella epidemic in Jiangsu Province, two dose Varv vaccination is recommended, the optimal time point for the second dose Varv is 3 years after the first vaccination.

Assessing vaccine effectiveness for varicella in Wuxi, China: a time-series analysis

OBJECTIVE

The varicella vaccine is not included in the national childhood immunization schedules in China. Varicella epidemics and outbreaks are frequently reported, and the evidence for the effectiveness of the varicella vaccine remains unclear. The aim of this study was to investigate varicella vaccine effectiveness in Wuxi, China.

METHODS

Varicella surveillance data were extracted from the China Information System for Disease Control and Prevention, and vaccination data were obtained from the Vaccination Integrated Service Management Information System of Jiangsu Province, China. Time-series analysis approaches were used to estimate varicella vaccine effectiveness.

RESULTS

A total of 16,093 varicella cases among children aged 1-6 years between January 2016 and December 2020 were analysed. A total of 217,297 children completed a two-dose varicella vaccination series. Compared with districts with lower vaccination rates, districts in Wuxi with higher varicella vaccination rates had a lower proportion of cases (p < 0.001). In the time-series approach, 0.8% fewer varicella cases were associated with a 1% increase in the two-dose varicella vaccination rate (p < 0.001), and similar effects were found in both the male and female populations.

CONCLUSIONS

Two-dose varicella vaccination was recommended as an effective health intervention to prevent varicella in Wuxi, China. Varicella vaccination is urgently needed in routine childhood immunisation programs.

Effectiveness of varicella vaccination during an outbreak in a large one-dose-vaccinated population in Shanghai

Emergency vaccination (EV) is used as effective postexposure prophylaxis (PEP) to control varicella outbreaks within 3-5 days. However, the advantages of a second dose of varicella vaccine (VarV) in students who had received one dose before an outbreak and the potential benefits of EV at more than 5 days after exposure have not been fully evaluated. This study evaluated the vaccine effectiveness (VE) of EV in preventing disease development during a varicella outbreak in Shanghai, China, in 2020. Questionnaires were used to obtain student demographic information, clinical manifestations, varicella history, vaccination status, and willingness to receive EV. The VE of EV was calculated as [1-relative risk (RR)] ×100%. Among the 1455 students included in this study, 31 cases were identified, resulting in an overall attack rate of 2.13%. There were 6 cases in unvaccinated students and 25 cases in one-dose-vaccinated students. A total of 788 students received one EV dose. The attack rates were 6.38% (6/94), 4.26% (19/446), 2.82% (2/71), and 0.56% (4/717) among unvaccinated students, students who received 1 dose of VarV, and students who received EV with the 1^st and 2^nd dose of VarV, respectively. Compared to that in unvaccinated students, the VE of EV with the 2^nd dose of VarV was 88% (95% CI 49% to 97%). EV should be performed as soon as possible after exposure. Nevertheless, vaccination is still recommended at more than 5 days post exposure to control varicella outbreaks.

A Dynamic Compartmental Model to Explore the Optimal Strategy of Varicella Vaccination: An Epidemiological Study in Jiangsu Province, China

Varicella (chickenpox) is highly contagious among children and frequently breaks out in schools. In this study, we developed a dynamic compartment model to explore the optimal schedule for varicella vaccination in Jiangsu Province, China. A susceptible-infected-recovered (SIR) model was proposed to simulate the transmission of varicella in different age groups. The basic reproduction number was computed by the kinetic model, and the impact of three prevention factors was assessed through the global sensitivity analysis. Finally, the effect of various vaccination scenarios was qualitatively evaluated by numerical simulation. The estimated basic reproduction number was 1.831 ± 0.078, and the greatest contributor was the 5-10 year-old group (0.747 ± 0.042, 40.80%). Sensitivity analysis indicated that there was a strong negative correlation between the second dose vaccination coverage rate and basic reproduction number. In addition, we qualitatively found that the incidence would significantly decrease as the second dose vaccine coverage expands. The results suggest that two-dose varicella vaccination should be mandatory, and the optimal age of second dose vaccination is the 5-10 year-old group. Optimal vaccination time, wide vaccine coverage along with other measures, could enhance the effectiveness of prevention and control of varicella in China.

Effectiveness of one-dose versus two-dose varicella vaccine in children in Qingdao, China: a matched case-control study

To evaluate whether two-dose of varicella vaccine would provide a better protection to children from varicella than one-dose, we conducted a 1:3 matched case-control study in children in Qingdao, China. A total of 509 varicella cases aged 6-11 y were collected from the China Information System for Disease Control and Prevention (CISDCP). And 1,527 controls, who did not suffer from varicella, were selected and matched with cases by age and class. The varicella vaccine effectiveness (VE) and corresponding 95% confidence interval (95% CI) were calculated. The vaccination coverage rate of one-dose varicella vaccine in the cases was 52.9%, while for the controls was 59.1%. And the two-dose vaccination rate in the cases and controls were 4.3% and 14.5%, respectively. A statistically significant difference was found in the immunization history between the cases and controls (P < .001).The overall varicella VE was 56.1% (95% CI: 45.0%-64.9%), and the VE of two-dose vaccination (81.6%, 95% CI: 70.5%-88.4%) was substantially higher than that of one-dose vaccination (44.7%, 95% CI: 31.6%-55.4%). For less than 2 y, 2-4 y, 4-6 y, and more than 6 y after only one-dose vaccination, the varicella VE were 96.6% (95% CI: 75.0%-99.5%), 81.2% (95% CI: 55.6%-92.0%), 60.8% (95% CI: 46.8%-70.2%), and 18.0% (95% CI: 4.3%-35.6%), respectively. The varicella VE gradually decreased over time (P for trend < 0.001). It is recommended that the coverage of varicella vaccine should be increased and two-dose of varicella vaccine should be included in the National Immunization Program of China.

Impact of a two-dose varicella immunization program on the incidence of varicella: a multi-year observational study in Shanghai, China

BACKGROUND

It remains hesitant to include a two-dose varicella vaccine (VarV) in a national routine immunization program in China. We aimed to quantify the impact of the two-dose VarV on varicella incidence in Shanghai.

RESEARCH DESIGN AND METHODS

We directly extracted the data of varicella cases and VarV doses in 2013-2020 in Shanghai, and then estimated the effects of two-dose VarV using a Serfling model.

RESULTS

A two-dose VarV immunization program has been extensively implemented since October 2017 and become free since August 2018 in Shanghai. Before and after this program, varicella cases significantly declined in children (P < 0.01), whereas did not in adults aged >18 years (P = 0.22). Compared to the predicted number of varicella cases, actual number was significantly lower by 8% in 2018 and 28% in 2019. Among children aged 4-6 years, the reduction in varicella cases was largest. Moreover, there was a significant reduction in varicella cases throughout 2020 (P < 0.001), in which the decrease due to social distancing for the COVID-19 was 54%.

CONCLUSIONS

A two-dose VarV immunization program may further reduce approximately one-third of varicella cases in Shanghai. Children <4 years and adults benefit less in this program, which warrants enhancing the immunization.

Evaluation of varicella vaccine effectiveness during outbreaks in schools or nurseries by cross-sectional study

OBJECTIVE

The aim of this study was to elucidate vaccine effectiveness (VE) during varicella outbreaks in schools and nurseries in Japan.

METHODS

An outbreak was defined as emergence of three or more cases of varicella within 21 days at the same institute. Clinical information such as varicella vaccination status, and history of varicella was collected. If a child had varicella during the outbreak, information about absences, fever, and disease severity was collected.

RESULTS

From September 2018 to January 2020, four outbreaks were reported around our institute from three elementary schools and one nursery. A total of 676 children were analyzed in this study. Seventy-six children (11.2%) were unvaccinated, 309 (45.7%) had received one dose of vaccine, and 291 (43.0%) had received two doses. Most children in Pre-K2 (1-2 years old) to Pre-K6 (5-6 years old), who were the targets of the national immunization schedule, received two doses. Meanwhile, most children older than third grade received single dose. Seventy-five children (11.1%) had varicella. Varicella prevalence from Pre-K5 to the third grade was greater than 10%. The adjusted VEs of single- and two-dose of varicella vaccine were 57.8% and 89.0%. The number of days absent was significantly longer in unvaccinated children than single-dose recipients (P = 0.0145). Unvaccinated children had significantly more severe skin eruptions than single-dose recipients (P = 0.0046) and two-dose recipients (P = 0.0258).

CONCLUSIONS

Although VEs of single-dose varicella vaccination during outbreaks was not high, the VE of two-dose vaccination was similar to that in a previously reported case-control study.

One single-center cross-sectional investigation on varicella antibody level of all age groups in Chinese people

Varicella outbreaks were mainly reported in developed regions with high vaccine coverage, but not in undeveloped areas. It is still not clear that whether the published data of varicella epidemiology could reflect the reality in China or not. In 2019, 657 subjects from People's Hospital of Chongqing Youyang County were included. Anti-varicella-zoster virus (VZV) IgG antibodies were determined by ELISA. The anti-VZV IgG levels were categorized as positive when values were ≥100 mIU/mL. Our results showed that the rates of anti-VZV IgG seropositivity (χ2 = 328.957, P < .0001) and geometric mean titers (P < .0001) were significantly influenced by age. The seropositivity declined dramatically from 84.5% in subjects ≤3 m of age, to 7.9% in subjects of >3 m-1 y (P < .0001). Then, the positivity rate increased slowly as age to 26.7% in >1-<3 y (P = .0006), and 34.5% in 3-<7 y (P = .4294). A steady rise (45.6%) in positivity was observed in subjects aged 7-<18 y. After then, the positivity began to increase robustly. A total of 87.8% of adults aged 18-<40 y had acquired VZV-specific immunity (P < .0001). The highest positivity rate was found in 40-<60 y  (98.3%) and ≥60 y (98.2%) group. In conclusion, most subjects of >3 m-<7 y age were susceptible to VZV. The proportion of subjects with natural infection-induced immunity increased with age. Nearly all subjects over 40 ages had positive anti-VZV IgG antibodies, which proved that they were infected by this virus in the past. These results suggested that VarV should be included in the national immunization program in China.

Uptrend prevalence of varicella parallel with low serum antibodies and low second-dose rate among children 10-14 years old in Wenzhou, China

In recent years, the incidence of varicella cases is rising, and outbreaks of varicella are frequently being reported worldwide. Our study aims to analyze the association between the varicella incidence and serum antibody level in the post-vaccine era. We retrieved and analyzed the incidence and prevalence data for children age 1-14 years in Wenzhou, China during 2010-2018. A cross-sectional seroepidemiology analysis was carried out in a series of 168 general healthy children age 1-14 years as well as children at a varicella outbreak in Wenzhou. Our data showed a significant surge in the incidence and prevalence of varicella in children aged 10-14 years in 2017 and 2018 while they were kept relatively stable in 2010-2016. The seroepidemiological analysis revealed a 7.3-fold significantly higher level of serum varicella IgG in healthy control students who exposed at the outbreak than that in general healthy children (median 523.5 vs. 71.7 mIU/mL, p < .01). The children 10-14 years old had the lowest rate of second-dose vaccination among the three age classes (7%, 41%, and 65% in 10-14, 5-9, and 2-4 age class, respectively), and children 5-9 years old who received the second dose had a higher level of serum protective IgG than those who did not (254.7 vs 98 mIU/mL, p = .06). The findings from the present study warn a two-dose vaccine schedule to reduce the climbing incidence and prevalence observed in the older children and suggest a higher serum IgG threshold for effective protection of children from the varicella outbreak.

Epidemiology of varicella and effectiveness of varicella vaccine in Hangzhou, China, 2019

Background: The varicella vaccine (VarV) is not included in the national childhood immunization schedules in China, although 2-dose VarV (VarV2) were recommended for children at 1 and 4 years of age in Hangzhou since 2014. However, the reported incremental vaccine effectiveness (VE) of VarV2 varies widely among studies. We described the epidemiological characteristics of varicella in Hangzhou, assessed the VE of VarV, so as to provide scientific evidence on optimization and adjustment of immunization strategies for varicella prevention in China. Methods: All varicella cases diagnosed in a hospital in Hangzhou are reported to China Information System for Disease Control and Prevention (CISDCP). The demographic information of reported varicella cases onset from January 1 to December 31, 2019 was extracted from CISDCP on Jan 31, 2020. The demographic information was obtained from the information system of the National Center for Disease Prevention and Control. We conducted a 1:1 matched case-control study to assess the effectiveness of VarV. Participant data were collected with standardized questionnaires. VarV vaccination status was checked by using Hangzhou Immunization Information System (HZIIS). Results: A total of 11,813 varicella cases were reported in Hangzhou, China, 2019, without any death. Annual estimated incidence of varicella was 120 cases per 100,000 populations in 2019. The overall estimated incidence rate of varicella was high, especially for persons aged 10-19 years old and in suburb areas. The seasonal pattern was apparent, mostly due to the cases among students and children in kindergarten. In total, 218 varicella cases and 218 matched controls were included for evaluating the VE of VarV. VarV vaccination produced a high level of protection against varicella, while VE of VarV2 was even better. VE of VarV1 was 91.0% (95%CI: 81.6%-95.8%), and VE was 98.0% (95.5%-99.2%) for VarV2. Conclusion: Continuous monitoring and management of varicella cases is necessary, especially in those endemic areas, high-risk populations, and peak periods; a 2-dose VarV strategy is highly recommended, and relevant health institutions should consider the inclusion of VarV in the national immunization program to better control varicella epidemic and reduce the burden of varicella.

Trend in varicella patients 4 years after implementation of universal two-dose varicella vaccination in Japan

OBJECTIVE

To elucidate the trend and clinical spectrum of virologically diagnosed varicella patients after implementation of universal vaccination as a national immunization program in Japan.

PATIENTS AND METHODS

Study subjects were patients suspected of varicella, less than 15 years of age, who visited 14 pediatric clinics in the Nagoya VZV Study Group from September 2015 to August 2019. Practitioners collected patient samples and information such as backgrounds, clinical symptoms, and previous immunization status. All patients were confirmed as having varicella based on molecular diagnostic assays.

RESULTS

Varicella zoster virus (VZV) DNA was detected in swab samples from 506 (83.1%) of the 609 suspected patients. The 455 varicella patients for whom vaccination status was available were divided into two groups: 180 universal vaccination targets and 275 non-targets. Numbers of monthly varicella patients decreased gradually during the observation period. In the 2016/17 season, the seasonal epidemic of varicella became undetectable in the universal vaccination target group, and starting in the 2017/18 season, it was obscured even in the non-target group. The median age of patients was significantly lower in the universal vaccination target group (3 years) than the non-target group (7 years) (P < 0.001). Vaccination status differed significantly between the two groups (P < 0.001). Most varicella patients were in the non-target group, especially those who had been vaccinated once (60.4%). Frequency of fever (P < 0.001) and number of skin rashes at the time of the first hospital visit (P = 0.001) were significantly higher in the non-target group.

CONCLUSIONS

Although the number of childhood varicella patients declined after implementation of national immunization with two doses of varicella vaccination, sporadic outbreaks still occurred, mainly in the non-universal vaccination target group. Insufficient vaccination of members of this group is likely to be a major reason for small local outbreaks.

Effects of Varicella Vaccine Time of First Dose and Coverage of Second Dose - Beijing and Ningbo, China, 2012-2018

What is already known about this topic?

The effectiveness of the two-dose vaccination schedule of varicella is better than that of one dose, but the vaccination schedule and coverage of varicella varies based on provinces in the mainland of China and has differing effects.

What is added by this report?

Earlier vaccination of the first dose may reduce the varicella incidence, and improving the vaccination coverage rates of the second dose will further reduce the varicella incidence.

What are the implications for public health practice?

Taking the first dose of vaccination promptly at 12 months old and improving the coverage of second dose of vaccination may play an important role in varicella prevention and control in China.

A Centralized Outbreak of Varicella among Children Attending Preschool in Suzhou, China

BACKGROUND

Varicella vaccine is available for voluntary purchase with a single dose currently recommended for children aged ≥12 months. An epidemiological study was undertaken in order to determine the characteristics of the outbreak, assess vaccine effectiveness, and examine risk factors for vaccine failure.

METHODS

A varicella case was defined as a generalized papulovesicular rash (without other apparent causes) in a child without prior varicella attending the kindergarten during February 22 to April 7 of 2016. Varicella among vaccinated children (breakthrough varicella) was defined as varicella occurring >42 days after vaccination. Children's vaccination status was verified with immunization records through local vaccination information platform.

RESULTS

Of the 738 children, 664 (90.0%) had no prior varicella history. Of these, 364 (54.8%) had received a single-dose varicella vaccine before outbreak. A total of 30 cases occurred in the outbreak, and 9 of them (30%) had breakthrough varicella. Age at vaccination (<15 months vs. ≥15 months) and time since vaccination before the outbreak (<3 years vs. ≥3 years) were not related to the occurrence of breakthrough varicella (P > 0.05). Single-dose varicella vaccination was 64.7% effective in preventing any varicella.

CONCLUSIONS

Single-dose varicella vaccine is effective in reducing the varicella attack rate, but not high enough to prevent outbreak. Timely detection and effective isolation are key factors in controlling varicella. Improving single-dose vaccination coverage and implementing two-dose vaccination strategy should be recommended to provide excellent protection to prevent varicella in the future in Suzhou.

Research about the optimal strategies for prevention and control of varicella outbreak in a school in a central city of China: based on an SEIR dynamic model

Varicella is an acute respiratory infectious diseases, with high transmissibility and quick dissemination. In this study, an SEIR (susceptible-exposed-infected-recovered) dynamic model was established to explore the optimal prevention and control measures according to the epidemiological characteristics about varicella outbreak in a school in a central city of China. Berkeley Madonna 8.3.18 and Microsoft Office Excel 2010 software were employed for the model simulation and data management, respectively. The result showed that the simulated result of SEIR model agreed well with the reported data when β (infected rate) equal to 0.067. Models showed that the cumulative number of cases was only 13 when isolation adopted when the infected individuals were identified (assuming isolation rate was up to 100%); the cumulative number of cases was only two and the TAR (total attack rate) was 0.56% when the vaccination coefficient reached 50%. The cumulative number of cases did not change significantly with the change of efficiency of ventilation and disinfection, but the peak time was delayed; when δ (vaccination coefficient) = 0.1, m (ventilation efficiency) = 0.7 or δ = 0.2, m = 0.5 or δ = 0.3, m = 0.1 or δ = 0.4 and above, the cumulative number of cases would reduce to one case and TAR would reduce to 0.28% with combined interventions. Varicella outbreak in school could be controlled through strict isolation or vaccination singly; combined interventions have been adopted when the vaccination coefficient was low.

Effectiveness and failure rate of the varicella vaccine in an outbreak in Jiangsu, China: a 1:2 matched case-control study

Background: The varicella vaccine is not included in the national childhood immunization schedules in China, although one-dose varicella vaccine has been suggested for susceptible children aged 1-12 years in Jiangsu Province. However, varicella epidemics and outbreaks are frequently reported. We investigated a varicella outbreak in an elementary school to explore the risk factors for varicella transmission and vaccine failure.Methods: A 1:2 matched case-control study was carried out. Participant data were collected with standardized questionnaires. For each case, we enrolled two controls: a subject with high exposure in the same classroom as the case and a subject with low exposure in a different classroom. Data regarding vaccination status and medical and exposure histories were analyzed.Results: Fifty-one cases were reported during the outbreak; 26 cases (51%) were breakthrough varicella. Varicella vaccine immunization history (P < .001, OR = 0.19, 95% CI = 0.08-0.45) and the presence of siblings (P = .037, OR = 0.45, 95% CI = 0.21-0.95) were protective factors in preventing varicella infection. Contact with varicella patients increased the risk of varicella infection (P = .028, OR = 3.39, 95% CI = 1.14-10.09). Breakthrough varicella cases tended to present a milder rash (P = .049), fewer complications (P = .02), fewer rash sites (P = .02) and a shorter duration of active lesions (P = .001). One pneumonia case and one encephalitis case were reported in breakthrough cases. Age <15 months at the time of vaccination increased the risk of breakthrough varicella (P = .012). The adjusted vaccine effectiveness was 81%.Conclusions: One-dose varicella vaccine is effective at alleviating clinical manifestations. The moderate coverage provided by one dose cannot prevent varicella outbreaks, and vaccination after 15 months of age should be considered in the immunization schedule; a two-dose strategy is highly recommended.

Clinical characteristics and risk factors associated with breakthrough varicella during varicella outbreaks

BACKGROUND

Although a varicella vaccine has been available in China since 1998 in the private sector, varicella outbreaks and breakthrough varicella (BV) still occur. In 2018, four varicella outbreaks with high BV rate sequentially occurred in four schools in Lu'an, sparking local public health authority's concerns on the varicella vaccine. Therefore, we conducted this investigation to evaluate varicella vaccine effectiveness (VE), characterize BV, and detect potential risk factors associated with BV.

METHODS

This was a three-stage study. First, a retrospective cohort study was done in each school to estimate the VEs of varicella vaccine  during outbreaks. Second, a descriptive epidemiological method was used to describe the characteristics of the four outbreaks and to compare the clinical characteristics between the BV cases and unvaccinated varicella cases. To identify the risk factors associated with BV, we conducted an unmatched case-control study in the third stage of the study.

RESULTS

A total of 199 cases were identified among four outbreaks, and the overall attack rate was 14%. Of 1203 students with available vaccination information, 822 (68%) were vaccinated at least once. The overall VEs among four outbreaks ranged from 19% to 69%, whereas the VE against moderate or severe varicella ranged from 74% to 90%. Compared with unvaccinated varicella cases, the moderate or severe varicella (p < .001) and fever (p = .029) in the BV group were less common. Besides, BV cases had a shorter duration of disease (p = .007). Children vaccinated more than six years before the outbreak had a higher risk of developing BV compared with those vaccinated within the past six years (OR = 2.4, 95% CI: 1.2-4.8). The risk of developing BV differed by the exposure intensity. Compared with the presence of three or fewer varicella cases in the same class, the OR was 7.8 (95% CI: 3.6-16.9) for four to nine cases in the same class and 25.2 (95% CI: 13.5 -47.2) for that of 10 or more cases.

CONCLUSIONS

The overall VE was insufficient to protect varicella infection, and the VE for moderate or severe varicella was only moderate. The manifestations of BV cases were generally milder than those seen in natural varicella infection. The time since vaccination and the intensity of exposure are risk factors for developing BV during an outbreak.

A persistent outbreak of varicella in a primary school in Dongguan City, Guangdong Province, China

Objectives

To describe the epidemiological features of a school varicella outbreak in Dongguan City, China, to identify the reasons underlying persistent spread, and to assess the effectiveness of the varicella vaccine.

Methods

We identified all cases during the outbreak. We described the outbreak epidemic course and examined the influence of the following variables on the outbreak: sleeping in the dormitory, eating in school, taking school transportation, hand-washing habits, morning examinations, and effectiveness of case isolation. Logistic regression was used to estimate the odds ratio and 95% confidence interval (CI) of contracting varicella.

Results

A total of 92 varicella cases were reported, accounting for 5.53% (92/1663) of all students. Among cases, 64.13% (59/92) were vaccinated. The outbreak lasted for 93 days and occurred in six generations. Vaccination coverage was between 78.05% and 85.67%. The varicella vaccine was effective in 56.63% of recipients (95% CI: 35.49–70.84%). Vaccine effectiveness significantly decreased after 4–6 years.

Conclusions

The varicella vaccine was unable to prevent virus spread even with high vaccination coverage. Delayed and inefficient isolation of cases was the primary cause of the persistent outbreak.

Spatiotemporal Epidemiology of Varicella in Chongqing, China, 2014-2018

Although immunization against varicella using vaccines has been proven to be significant and effective in the past decades, varicella remains a major public health concern for many developing countries. Varicella vaccination has not been introduced into routine immunization programs in China, and varicella outbreaks have continued to occur. Taking the city of Chongqing, which has a high prevalence of varicella, as an example, this study explored the spatiotemporal epidemiology of varicella. Based on the reported data of varicella cases from 1 January 2014 to 31 December 2018 in Chongqing, hot spots and space-time clusters of varicella were identified using spatial autocorrelation analysis and scan statistics. Within this period, a total of 112,273 varicella cases were reported in Chongqing (average annual incidence: 73.44 per 100,000), including one death. The incidence of varicella showed an increasing trend with significant seasonal peaks, which occurred during April to July and October to January of the following year. The total ratio of male to female patients affected was 1.10:1. Children under the age of 15 and students accounted for the majority of the patient population. The hotspots detected through local spatial autocorrelation analysis, and the most likely clusters identified by scan analysis, were primarily in the main urban districts of Chongqing. The secondary clusters were mostly detected in northeast and southwest Chongqing. There were obvious spatial dependence and spatiotemporal clustering characteristics of varicella in Chongqing from 2014 to 2018. High-risk districts, populations, and peak periods were found in this study, which could be helpful in implementing varicella prevention and control programs, and in adjusting vaccination strategies for the varicella vaccine based on actual conditions.

Analysis of sero-epidemiological characteristics of varicella in healthy children in Jiangsu Province, China

Background

In recent years, outbreaks of varicella have continued to occur, and the coverage rate of varicella vaccine in Jiangsu Province, China, remains unclear. This study aims to analyse the levels of immune antibody against varicella and obtain a comprehensive understanding of the varicella attenuated live vaccine (VarV) coverage rate in children aged 1–9 years in Jiangsu Province.

Methods

From June to October 2016, a cross-sectional survey was conducted to collect 3631 serum samples from healthy children aged 1–9 years in Jiangsu Province. The immunoglobulin G (IgG) antibody levels of varicella were detected by enzyme-linked immunosorbent assay (ELISA).

Results

The VarV coverage rate of healthy children was only 43.1% (95% CI: 41.1–44.7%). The seroprevalence after vaccination with a single dose of VarV was only 57.1%, and the overall seropositivity and geometric antibody titre (GMC) were 43.5% and 225.4 mU/ml, respectively. The seropositivity was significantly higher in girls than in boys (χ² = 18.82, P < 0.001). The difference in seropositivity between the 5–9 age group and 1–4 age group was statistically significant (χ² = 84.31, P < 0.001). The difference in seropositivity between different regions was statistically significant, with the highest seropositivity in the northern area, 53.7% (χ² = 35.64, P < 0.001). The seropositivity in the group receiving one dose of VarV was significantly higher than that of the unvaccinated group (χ² = 205.16, P < 0.001). Linear regression analysis suggested that the GMC of varicella antibodies wanes with the time since vaccination (F = 65.01, P = 0.002).

Conclusion

The VarV coverage rate of healthy children in Jiangsu Province was low. Sero-conversion rates were also low after one dose of VarV, and the immune effectiveness of a single dose of VarV was limited. To control the spread of varicella, VarV should be included in the routine immunization program, and strengthened immunization measures for the varicella-susceptible population warrant additional consideration.

Effectiveness of post-exposure prophylaxis during varicella outbreaks among primary and middle school students in Shanghai: An analysis of three-year surveillance data

OBJECTIVES

To evaluate the effectiveness of post-exposure prophylaxis conducted during varicella outbreaks among students in Shanghai.

METHODS

Surveillance data were collected from September 1, 2013 to December 31, 2016 involving 3524 susceptible students in 109 primary and middle school classes where emergency vaccinations (EVs) had been administered. Students were divided into two groups according to their prior vaccination (PV) varicella vaccine status. A secondary attack rate was used to compare EV and non-EV groups using a chi-squared test. Stratification analyses were performed, adjusting for the EV administration date, the vaccination coverage rate, and the number of cases prior to the EV.

RESULTS

The effectiveness rate was 92.2% (95% confidence interval (CI): 37.1-99.0%) when EV was applied within 3 days following the outbreak onset date, and 95.2% (95% CI: 79.9-98.8%) when vaccination coverage was ≥80% among students with PV. When students with PV received an EV for varicella within 3 days, the effectiveness rate was 100%.

CONCLUSIONS

EV showed high protective effectiveness for varicella during outbreaks, especially if administered within 3 days of an outbreak and in conjunction with a high coverage rate.