An epidemiological analysis of chickenpox. Prevalence, risk factors, and prevention strategies

Nº de DOI: 10.34896/RSI.2026.71.54.002

AUTHORS

1. Jodie Jaqueline Gaibor Fuentes. General Practitioner with a University Master’s Degree in Precision Nutrition and Nutritional Epidemiology. Affiliated with Centro Urológico UROCORP. Graduate of Universidad de Guayaquil. Based in Guayaquil, Ecuador. https://orcid.org/0000-0003-0324-1419
2. Johana Katherine Asas Jinde. General Practitioner with a Master’s Degree in Occupational Health and Safety. Affiliated with Hospital Marco Vinicio Iza. Graduate of Universidad Central del Ecuador. Based in Lago Agrio, Ecuador. https://orcid.org/0000-0002-7934-1048
3. Pablo Andrés Endara Alpusig. General Practitioner. Affiliated with Clínica de Especialidades Medycin. Graduate of Universidad Regional Autónoma de los Andes. Based in Latacunga, Ecuador. https://orcid.org/0009-0005-6433-2391
4. Nathaly Jeanneth Lombeida Correa. General Practitioner with a Master’s Degree in Public Health. Affiliated with the Agencia Metropolitana de Tránsito. Graduate of Universidad Central del Ecuador. Based in Quito, Ecuador. https://orcid.org/0009-0000-9788-265X
5. Elsa Marianela Tapia Cevallos. Master’s Degree in Education. Graduate of Universidad Tecnológica América. Based in Ibarra, Ecuador. https://orcid.org/0009-0002-6457-6976

SUMMARY

This paper provides an epidemiological description of chickenpox by studying the occurrence and distribution of chickenpox based on various regions and populations, identifying risk factors for developing severe disease associated with chickenpox, and evaluating the efficacy of current prevention measures to improve public health policies designed to reduce the impact of chickenpox and protect high-risk groups globally.

KEY WORDS

Chickenpox, varicella-zoster virus, epidemiology, vaccination, risk factors, immunization.

RESUMEN

Este artículo ofrece una descripción epidemiológica de la varicela mediante el estudio de su incidencia y distribución en diversas regiones y poblaciones, la identificación de factores de riesgo para desarrollar formas graves de la enfermedad y la evaluación de la eficacia de las medidas de prevención actuales, con el fin de mejorar las políticas de salud pública destinadas a reducir el impacto de la varicela y proteger a los grupos de alto riesgo a nivel mundial.

PALABRAS CLAVE

Varicela, virus varicela-zóster, epidemiología, vacunación, factores de riesgo, inmunización.

INTRODUCTION

The varicella-zoster virus causes a highly contagious disease called chickenpox (varicella). Chickenpox is not only an acute childhood disease, but it can also cause serious health problems in adolescents, adults, pregnant women, people with weakened immune systems, and newborns. These groups are at higher risk for developing serious complications associated with chickenpox. The chickenpox epidemiology has a worldwide variability with respect to the number of cases occurring; higher than average incidence rates of chickenpox occur in areas where vaccination programs are either lacking or nonexistent, and distinct patterns of incidence by age reveal that while children are primarily affected by chickenpox, outbreaks occur frequently among adolescent and adult populations residing in areas with low vaccination coverage. Chickenpox typically presents as a classic skin rash composed of many small itchy blisters, although laboratory testing can be utilized for diagnosing atypical or complicated cases. Risk factors that can increase the severity of disease include underlying health issues such as immunosuppression, pregnancy, and lack of prior immunity (natural or from vaccination); these risk factors increase the probability of developing severe disease or being hospitalized as a result of chickenpox. The implementation of effective vaccination strategies (one- and two-dose varicella immunization) has dramatically changed the epidemiology of chickenpox (i.e., incidence of disease, number of outbreaks, etc.), especially in geographic areas where universal pediatric immunization programs are in place. Despite advances in vaccination, outbreaks of chickenpox continue to occur; therefore, a comprehensive approach to prevention and control is necessary, including targeted vaccination efforts aimed at high-risk groups and outbreak management guidelines.

OBJECTIVE

To analyze the epidemiology, clinical characteristics, risk factors, vulnerable populations, and prevention strategies associated with chickenpox, as well as to evaluate the impact of vaccination programs on reducing disease incidence, complications, and outbreaks worldwide.

METHODOLOGY

This paper was developed as a narrative review of the literature focused on the epidemiology, clinical presentation, risk factors, vulnerable populations, immunity, and prevention strategies related to chickenpox. Relevant scientific publications, epidemiological reports, and public health sources addressing global and regional patterns of varicella were reviewed and analyzed. The selected studies included population-based epidemiological investigations, clinical reviews, vaccination effectiveness studies, and public health analyses that provided evidence on disease incidence, age distribution, complications, and immunization outcomes. The information was organized into thematic sections in order to synthesize current knowledge regarding the burden of chickenpox, the determinants of severe disease, and the impact of vaccination programs on disease control. This methodological approach allowed the integration of evidence from different populations and regions to provide a broad public health perspective on chickenpox and its prevention.

RESULTS

Epidemiological Profile of Chickenpox:

What are the global and regional prevalence rates of chickenpox?

Geographical and temporal variation exists in how many people have chickenpox worldwide and in individual regions. This shows that chickenpox continues to be a public health issue. For example, in Chongqing, China, data obtained from population-based epidemiological study of the number of cases reported has shown an increase in the number of cases of chickenpox in Chongqing, the average annual rate of chickenpox was 88.3 per 100,000 and the peak rate was 133.85 cases per 100,000 (in 2019)¹. The peak rate at which cases were reported was higher than the average number reported nationally indicating that Chongqing is especially at risk relative to other areas of China¹. Additionally, regional trends appear to be similar across other regions of China, indicating that there may be some interconnectedness among various factors (e.g., population density, vaccination, access to healthcare) at play with respect to prevalence rates¹. Importantly, even though cases have increased in Chongqing, case reports have shown declines for the time period between 2020 and 2023, which would likely be a result of increased vaccination efforts as well as due to the implementation of COVID-19 containment measures, which inadvertently reduced the spread of other infectious diseases such as chickenpox¹. The interplay of local epidemiological data, national level trends, and international health initiatives will require the continued surveillance and monitoring of cases to improve the immunization program (increase immunization rates) and improve public health practices to manage and reduce the burden of chickenpox regionally and internationally.

How does chickenpox incidence vary among different age groups and populations?

The incidence of chickenpox is highly variable by population and by age group and has been influenced by a variety of historical factors such as exposure to the disease, vaccination practices, and acquired immunity. Prior to widespread vaccine use in 1995, respectively, a significant proportion of children contracted chicken pox; particularly, virtually all children became infected with chickenpox as children (predominantly ages 3 to 6 in unvaccinated populations)². The implementation of routine childhood immunization has had a profound impact on the epidemiology of chickenpox, as there has been marked (nearly 90%) reduction in the number of chickenpox cases and altered the age distributions of children who are susceptible to chickenpox². In the U.S., where most children receive the varicella vaccination, few children contract the disease. As a result, there is ongoing risk for unvaccinated adults and older adults who never contracted chickenpox nor were vaccinated, given that there is no upper age limit for contracting the disease and as long as immunity has not been acquired, exists throughout one’s life [2]. Furthermore, adults who contract chickenpox have a greater risk of experiencing severe disease than do children, which highlights the interplay among age group, immunity status, and disease severity in the population². Because of this, it is important that public health professionals continue to monitor, provide targeted vaccination opportunities, and educate regarding the residual vulnerabilities of older and unvaccinated individuals, thus ensuring that all members of society benefit from the reduction of incidence of chickenpox².

What clinical features are most common in chickenpox presentations?

The unique clinical characteristics of chickenpox, which generally manifest in a predictable pattern, and the prodromal manifestations (such as low-grade fever, malaise, and flu-like symptoms) usually occur 1-2 days before the characteristic rash appears, show a strong relationship between systemic and dermatological manifestations of this disease^3,4,5. The blister-like lesions of chickenpox are usually considered the most common clinical feature of the disease and may be observed as early as 1-2 days after the onset of prodromal symptoms. The rash usually presents on the face and trunk and then spreads to the remaining body areas (scalp) with small blisters as indicative lesions for chickenpox^4,5,6. The rash also has multiple stages of development (macule, papule, vesicle and crust) occurring simultaneously, thereby making it a central part of the diagnosis and clinical evaluation of chickenpox and providing an indication of the wide range of cutaneous involvement associated with the disease^3,5. The constellation of chickenpox clinical symptoms (including the presence of fever and a polymorphic rash), as well as the inter-relationship between the two symptoms, is critical to the identification of chickenpox and to distinguishing it from other exanthems in children, thus underscoring the need for thorough clinical evaluation and history to confirm a diagnosis and guide the development of management strategies [5][4]. Therefore, early recognition and identification of these features as part of a comprehensive strategy for disease control and prevention of complications from chickenpox are especially important in populations with different degrees of susceptibility (age) or immune disease (immunocompromised).

Risk Factors and Vulnerable Populations:

Which individuals are at increased risk of severe chickenpox complications?

Individuals in a variety of situations are at increased risk for severe complications due to chickenpox (varicella-zoster virus), and understanding the interaction of the multiple at-risk populations with chickenpox is essential to appropriately managing these issues with respect to clinical care and implementing effective public health measures. While infants and very young children are at a unique and identifiable risk because of their immature immune systems, which significantly hinder their ability to mount an effective immune response to the varicella-zoster virus and increase their risk of developing complications, such as secondary bacterial infections or needing to be hospitalized^7,8. As a second example, adolescents and young adults are also identified as at risk, although they are often overlooked, particularly adolescents, as evidence indicates that adolescents and young adults develop more severe clinical manifestations of chickenpox than infants or children; therefore, they require timely medical evaluation, and in some situations, will require antiviral medications^7,9. As a third identifiable at-risk population, pregnant women are at risk of developing serious medical complications from chickenpox during pregnancy, and their developing fetus is also at risk of developing congenital varicella syndrome and/or neonatal complications associated with chickenpox^7,8,9. Individuals with a depressed immune system are at particular risk for the development of severe or potentially life-threatening complications from chickenpox, regardless of the cause of their immunodeficiency (e.g., primary immunodeficiency disorders, HIV infection, cancer treatment, immunosuppressive medications). Timely medical attention and consideration for the use of antiviral therapy are critical for these individuals; therefore, it is also important to understand the overlaps between these at-risk populations (e.g., pregnant women who are immunocompromised, and/or hospitalized children), which demonstrates the interconnected nature of the domains of risk and the importance of implementing targeted measures to mitigate the burden of severe complications associated with chickenpox by providing ongoing clinical monitoring and initiating antiviral therapy as soon as possible for those at increased risk for severe complications due to chickenpox⁹. Because of the multiple-risk factors found in the described populations above, effective prevention measures, timely diagnosis, and prompt initiation of therapy are necessary to reduce the impact of severe complications associated with chickenpox in these high-risk populations.

How do underlying health conditions influence chickenpox outcomes?

Underlying medical conditions greatly modify the clinical course and outcome for patients infected with varicella. For instance, adults tend to have more severe disease than do children and statistically have a greater risk of death from varicella than do children. This fact has been documented in numerous epidemiologic studies¹⁰. In addition, certain populations such as pregnant women, infants < 1 year old, and those with immunocompromised systems are particularly vulnerable to the severe, often life-threatening complications of varicella¹¹.

Varicella is another example where the interrelationship between comorbidities and the use of aggressive therapies (e.g., antiviral medications such as acyclovir) is clear. The increased vulnerability that individuals have from comorbidities often leads them to require aggressive therapies (e.g., antiviral medication) in order to have a successful outcome. On the other hand, patients with no underlying medical conditions typically have successful outcomes with supportive care alone. Therefore, there is a considerable difference in how someone’s health status can predict the outcome of varicella and also the degree of intervention required in order to facilitate recovery¹¹. Therefore, it is important for public health policy and clinical guidelines to focus efforts on the early identification and appropriate management of at-risk populations by implementing active surveillance and immunization strategies to reduce the disproportionate burden of disease experienced by those with underlying medical conditions.

What role does immunity (natural or vaccine-induced) play in susceptibility?

Interrelations between natural and immunity acquired via vaccination, play an important role in determining an overall risk of susceptibility to infectious diseases (i.e., chickenpox and its associated complications), especially among different age groups. Immunity acquired either through a natural infection or through vaccination provides the immune system with the ability to recognize target pathogens, ultimately decreasing the chance of subsequent infection¹². Both types of immunity will induce antibody production and T-cell production, thereby forming the basis of active immunization which provides long-lasting protection against a specific disease¹². The strength and longevity of immunity obtained via natural infection versus vaccination can differ; that is, while natural infection typically produces a strong and often more comprehensive immune-response, the risk associated with obtaining immunity via natural infection is higher than that associated with obtaining immunity via vaccination especially among high-risk populations (older adults or those with impaired immunity) ¹³. Conversely, immunity obtained via vaccination provides a means by which to safely obtain immunity to the pathogens without incurring the morbidity, mortality and long-term effects associated with the acquisition of immunity via a natural infection¹³. The degree of immunity acquired through either prior infection or prior vaccination will impact a person’s susceptibility to the disease and therefore accounts for the ongoing high susceptibility of unvaccinated children to develop chickenpox, as well as the potential susceptibility of elderly persons who did not develop the disease through natural infection or received the disease through a vaccine to develop chickenpox later in life¹³. This interconnected relationship also illustrates the continued need for both immunization programs as well as targeted interventions needed to decrease susceptibility to disease across all affected demographic groups, thereby continuing the need for maintaining public health initiatives aimed at ensuring adequate vaccine coverage and protection for high-risk populations.

Prevention and Control Strategies for Chickenpox:

How effective are current varicella vaccination regimens (1- or 2-dose) in preventing outbreaks?

A comparison of the effectiveness of a single-dose versus a two-dose varicella vaccination regimen shows connections between the individual and population health outcomes associated with the vaccinations, vaccine policy, and outbreak management. While the usage of a single-dose regimen resulted in a substantial decrease in incidence of varicella soon after implementation, there has been a consistent trend of breakthrough infections occurring at high levels following vaccination; for example, there was a steady rate of 7.2% of vaccinated persons experiencing varicella within 10 years of receiving the vaccine, and outbreaks were not truly prevented by the one-dose coverage, especially in high population density areas (e.g., schools)¹⁴ . The implementation of a two-dose regimen has resulted in a significant reduction in varicella incidence and hospitalization, and outbreaks, not only through direct immunity to vaccinated individuals but by increasing herd immunity thus decreasing transmission to vulnerable (those that cannot get the varicella vaccine e.g., infants, adults) populations¹⁴. The long-term follow-up studies estimate that vaccine effectiveness for any varicella disease occurred at over 98% for 10 years following vaccination, and that there was 100% effectiveness in preventing severe varicella disease; in fact, severe varicella disease and it’s associated complications would essentially be eliminated by immunization using a two-dose regimen¹⁴. These results illustrate the need for strong two-dose varicella immunization policies and catch-up immunization for under-immunized populations in order to achieve optimum outbreak prevention and maintain a high level of population protection.

What is the impact of universal pediatric immunization programs on chickenpox epidemiology?

In addition to lowering the incidence of chickenpox (varicella) among the population of wall‐to‐wall vaccinated states with comprehensive pediatric immunization programs, the incidence of chickenpox has also changed the way the population exhibits its incidence (or pattern) and clinical presentation. Since the implementation of routine childhood vaccination against chickenpox, there has been a measurable decline in both incidence and severity of all varicella cases, thereby demonstrating their efficacy in terms of public health initiatives¹⁵.

Despite the potential that there could be a greater proportion of older children, adolescents, or adults developing varicella (and therefore a larger age distribution for such cases), there continues to be a substantial decline in both morbidity and mortality in these cases as a result of vaccination; therefore, this shift does not negate the overall decline in morbidity and mortality associated with chickenpox due to the introduction of universal pediatric varicella immunization/ vaccination programs¹⁵. Because children are the main source of the varicella-zoster virus, vaccination programs aimed at children also provide an opportunity for these programs to indirectly protect more vulnerable populations, such as adults and those who have weakened immune systems from acquiring or transmitting the virus when there is community exposure and/or an outbreak¹⁵. Furthermore, when vaccinated individuals develop breakthrough cases of chickenpox, the severity of the disease in those who experience breakthrough cases is significantly reduced; therefore, vaccination of children continues to decrease the overall public health burden associated with chickenpox among the entire community¹⁵. The numerous interrelated factors associated with the implementation of a comprehensive pediatric varicella immunization/vaccination program emphasize the continued and widespread implementation of such programs because they have proven to be effective in both reducing the total number of cases of chickenpox and in protecting at-risk populations from acquiring the disease and in reducing the overall impact of chickenpox on the healthcare system.

DISCUSSION 

The findings from this epidemiological study point out that vaccination programs play an important role in controlling both the number and severity of chickenpox cases as evidenced by this and other prior studies discussing vaccination as the primary form of prevention.

Regional increases in incidence, particularly Chongqing, emphasize how many factors have an effect on varicella transmission dynamics and therefore incidence rates including:

– The population density of a particular region.

– The amount of access to health care.

– The level of vaccination coverage.

As determined by other studies which have examined factors influencing varicella transmission, we see that the observed increase in the incidence of varicella cases in Chongqing, has been influenced by population density, access to healthcare and vaccination coverage. The decrease in the number of varicella cases following the introduction of COVID-19 containment measures provides additional support for the hypothesis that non-pharmaceutical interventions can decrease the spread of a condition, but there are no long-term conclusions regarding the efficacy of these methods.

The shift in susceptibility toward unvaccinated adults/elderly highlights the necessity for a vaccination program that incorporates all high-risk groups (because they are at an increased risk for developing serious complications associated with varicella such as pneumonia and encephalitis). The very high efficacy of the two-dose vaccines is indicative of the need for continued public health efforts to educate the general public to complete vaccination schedules, however the existence of breakthrough infections, albeit milder, indicates that immunity from the vaccine may not last as long as originally thought and/or be less effective against some strains of varicella zoster virus.

Limitations associated with the study include possible underreporting, as well as an incomplete dataset particularly in rural/underserved areas of the country; therefore the actual number of cases is likely to be grossly underestimated. Further, while vaccination was the primary focus of this study, there were no data collected regarding other socio-economic and behavioral factors that may have had an impact on vaccine acceptance and coverage.

Future research efforts should focus on examining long-term durability of immunity following vaccination, developing newer more efficacious vaccines, and examining ways to improve vaccination uptake across all diverse populations. Continuous surveillance as well as using modification to current public health approaches will be necessary to continue to monitor new epidemiological trends and to maintain control of varicella.

In conclusion, the results of this study provide useful information regarding the epidemiology/genetics of chickenpox and reinforce the justification for implementing integrated prevention strategies (vaccination, outbreak control and ongoing monitoring) in order to reduce the global burden of varicella.

CONCLUSIONS

Chickenpox remains an important public health concern despite the substantial progress achieved through vaccination. Its epidemiological distribution varies across regions, age groups, and healthcare settings, with higher incidence and more frequent outbreaks occurring in populations with insufficient vaccination coverage. Although the disease is often self-limited in childhood, adolescents, adults, pregnant women, newborns, and immunocompromised individuals continue to face a significantly greater risk of severe complications, hospitalization, and adverse outcomes.

The findings of this review demonstrate that immunity, whether naturally acquired or vaccine-induced, plays a central role in reducing susceptibility and disease severity. At the same time, the evidence strongly supports the superiority of the two-dose varicella vaccination regimen over the one-dose strategy in preventing outbreaks, reducing breakthrough infections, and minimizing severe disease. Universal pediatric immunization programs have significantly reduced the burden of varicella, not only in vaccinated children but also indirectly in vulnerable populations through decreased transmission.

However, persistent outbreaks, incomplete vaccine coverage, and the continued presence of susceptible high-risk groups indicate that varicella control requires more than routine childhood vaccination alone. Integrated prevention strategies, including improved surveillance, catch-up vaccination, targeted protection of vulnerable populations, outbreak response measures, and public health education, remain essential. Continued research is also needed to better understand long-term vaccine-induced immunity and to optimize vaccination policies in diverse epidemiological contexts. Overall, strengthening comprehensive prevention and control strategies will be crucial to further reduce the global burden of chickenpox and protect populations at greatest risk.

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