Severe Varicella in Children Under Five Years of Age in the Context of Herd Immunity, Vaccine Hesitancy, and the COVID-19 Pandemic in Brazil, 2008-2023.
- 1Department of General and Specialized Surgery, Postgraduate Maternal Child Health Program, Faculty of Medicine, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil.
- 2Faculty of Medicine, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil.
- 3Postgraduate Maternal Child Health Program, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil.
Abstract
Objective
Varicella (chickenpox) is a highly contagious disease, and its vaccine was incorporated into the Brazilian National Immunization Program in 2013. Objectives: (i) To analyze trends in hospitalization rates for severe chickenpox by age; (ii) To assess the impact of the interventions "anti-vaccine movement/vaccine hesitancy" and "COVID-19 pandemic" on hospitalization rates.Materials and methods
Classical Time Series (CTS) and Interrupted Time Series (ITS) methods were applied to estimate the impact of the anti-vaccine movement/vaccine hesitancy (intervention-1) that occurred in 2016 and the COVID-19 pandemic (intervention-2) that began in 2020 on hospitalization rates among children under 5 years old, stratified by groups based on vaccine-ineligible (< 1 year old) and vaccine-eligible (1-4 years old) children.Results
CTS results supported the potential for herd immunity effects, showing an annual decline of -17% and -14% in hospitalization rates for vaccine-eligible (1-4 years) and vaccine-ineligible (< 1 year) groups, respectively. The ITS model for vaccine-ineligible children showed an upward trend (coefficient 0.35) after intervention-1(isolate) (p=0.001), as well as after intervention-1 (coefficient 0.42; p 0.011) adjusting for intervention-2 (p=0.135). For vaccine-eligible children, the ITS model revealed an upward trend (coefficient 0.14) only after intervention-1 (isolate) (p=0.006).Conclusion
The decline in varicella hospitalizations indicates a herd immunity effect among vaccine-ineligible children. ITS analysis reveals that the anti-vaccine movement/vaccine hesitancy contributed to increased hospitalizations in both vaccine-eligible (1-4 years) and vaccine-ineligible (<1 year) groups, while the COVID-19 pandemic had no discernible impact.
Related
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BibTeX
@article{nascimento2026severe,
title = {{Severe Varicella in Children Under Five Years of Age in the Context of Herd Immunity, Vaccine Hesitancy, and the COVID-19 Pandemic in Brazil, 2008-2023.}},
author = {Maria Isabel do Nascimento and Alcenir Tavares Valente Junior and Beatriz de Vasconcelos Falcão and Marina Pereira da Silva and Mauricio Souza Leão},
journal = {Journal of family \& reproductive health},
year = {2026},
month = jun,
doi = {10.18502/jfrh.v20i2.22614},
url = {https://europepmc.org/article/MED/42923831},
note = {CC BY-NC},
}
RIS
TY - JOUR
TI - Severe Varicella in Children Under Five Years of Age in the Context of Herd Immunity, Vaccine Hesitancy, and the COVID-19 Pandemic in Brazil, 2008-2023.
AU - Maria Isabel do Nascimento
AU - Alcenir Tavares Valente Junior
AU - Beatriz de Vasconcelos Falcão
AU - Marina Pereira da Silva
AU - Mauricio Souza Leão
PY - 2026
DA - 2026/06/01
JO - Journal of family & reproductive health
DO - 10.18502/jfrh.v20i2.22614
UR - https://europepmc.org/article/MED/42923831
AB - Objective Varicella (chickenpox) is a highly contagious disease, and its vaccine was incorporated into the Brazilian National Immunization Program in 2013. Objectives: (i) To analyze trends in hospitalization rates for severe chickenpox by age; (ii) To assess the impact of the interventions "anti-vaccine movement/vaccine hesitancy" and "COVID-19 pandemic" on hospitalization rates.Materials and methods Classical Time Series (CTS) and Interrupted Time Series (ITS) methods were applied to estimate the impact of the anti-vaccine movement/vaccine hesitancy (intervention-1) that occurred in 2016 and the COVID-19 pandemic (intervention-2) that began in 2020 on hospitalization rates among children under 5 years old, stratified by groups based on vaccine-ineligible (< 1 year old) and vaccine-eligible (1-4 years old) children.Results CTS results supported the potential for herd immunity effects, showing an annual decline of -17% and -14% in hospitalization rates for vaccine-eligible (1-4 years) and vaccine-ineligible (< 1 year) groups, respectively. The ITS model for vaccine-ineligible children showed an upward trend (coefficient 0.35) after intervention-1(isolate) (p=0.001), as well as after intervention-1 (coefficient 0.42; p 0.011) adjusting for intervention-2 (p=0.135). For vaccine-eligible children, the ITS model revealed an upward trend (coefficient 0.14) only after intervention-1 (isolate) (p=0.006).Conclusion The decline in varicella hospitalizations indicates a herd immunity effect among vaccine-ineligible children. ITS analysis reveals that the anti-vaccine movement/vaccine hesitancy contributed to increased hospitalizations in both vaccine-eligible (1-4 years) and vaccine-ineligible (<1 year) groups, while the COVID-19 pandemic had no discernible impact.
SN - 1735-8949
SN - 1735-9392
ER -