Time series analysis of the chickenpox rate and the impact of vaccine implementation in Tucumán

Abstract

INTRODUCTION: Chickenpox is one of the most common vaccine-preventable diseases. In 1998, the World Health Organization
recommended incorporating the vaccine into national vaccination programs. In Argentina, it was implemented in 2015. The objective of the study was to analyze the varicella time series in Tucumán during 2005-2019 and to evaluate the impact of the  chickenpox vaccine on its  incidence in Tucumán after its implementation. METHODS: An ecological observational study was  performed using secondary data sources. Chickenpox cases were those reported by the National Health Surveillance System. A  description of the time series of reported chickenpox cases for Tucumán was made, and generalized additive models (GAM)  were constructed using a negative binomial distribution. The impact of the vaccine was assessed by considering the period  2005-2014, a GAM model was constructed, and the most probable behavior was predicted for the following years (2015-2019).  The impact was evaluated by comparing predicted and observed rates with their confidence intervals. RESULTS: Tucumán  reported 82,810 cases during 2005-2019. The annual rate varied between 1.66 per 1000 inhabitants (2019) and 6.04 per 1000  inhabitants (2007). The series showed seasonality and in recent years a decreasing trend. A significant decrease in the incidence  rate was observed after vaccine implementation. DISCUSSION: This work showed the impact of implementing public  policies such as vaccines.