Impact of single-dose varicella vaccination in Argentina, by province: a time series study.

Introduction. Argentina implemented the varicella vaccine in 2015. This study aimed to evaluate the impact of vaccine implementation in each province of Argentina. Materials and methods. An observational, ecological analytic study using secondary data sources. We performed a time series description of varicella cases and built generalized additive models using a negative binomial distribution. We modeled the behavior of varicella in the period 2005-2014 and made a forecast of the most likely behavior until 2019. We assessed the impact by comparing expected and observed incidence rates. We studied whether 2015 was a turning point in the incidence trend in each jurisdiction. We used R and Joinpoint software. Results. Between 2005 and 2019, Argentina had an incidence rate of varicella of 5.93 cases/100,000 population. At the national level, the incidence rate significantly decreased after 2015. In Argentina in general and in 6 provinces, 2015 was a breakpoint, whereas in the rest of the provinces, it occurred before (n = 2) or after (n = 1), or there was none in the time series analyzed (n = 15). Conclusions. The work demonstrates the impact of vaccine implementation in each of Argentina's provinces and highlights the importance of evaluating national policies at the provincial level.