Varicella

Varicella (chickenpox) is the primary infection caused by varicella-zoster virus (VZV). More than 90% of the children in most European countries contract varicella in the first 10–12 years of life, in Italy the incidence is slightly lower, possibly due to the warmer climate and lower rates of day-care attendance. The aim of the present study was to examine trends in age-specific varicella incidence, as well as incidence of hospitalizations linked to varicella, among children and adolescents, following the introduction of a universal varicella vaccination in Veneto, Italy. Another goal of the study was to apply specific statistical models able to identify the timing of significant varicella incidence drops, following the beginning of the vaccination, so to assess vaccine effectiveness under field conditions. Finally, it was provided an estimate of avoided varicella cases and hospitalizations due to varicella as a consequence of the universal vaccination. 

We calculated the number of varicella cases and crude annual rates of varicella-related events by calendar year and age group (<1, 1–4, 5–9, 10–14, and 15 years or older). 
Age-specific population sizes to calculate the incidence of varicella were obtained from the Italian National Institute of Statistics (ISTAT) website. Rates of varicella hospitalizations were calculated as the number of hospitalizations for varicella, extracted from the SDO, in relation to the population at risk at the beginning of each calendar year. The population at risk was constituted of the resident population in the region, with figures obtained for the period 2000–2008 from the ISTAT website. 

The vaccine coverage rate was 6.8% in the 2004 birth-cohort and 78.6% in the 2008 cohort. Varicella incidence in 0–14 year-olds was 6136.8/100,000 person-years in 2000 and 4004.8 in 2008; hospitalization rates were 18.7 and 8.4. Incidence rates significantly decreased 2.5 years after beginning the universal vaccination, while hospitalization rates showed a significant decrease one year earlier. There was a remarkable decline of both varicella incidence and hospitalizations especially in 1–4 year-old children. This study confirms the positive impact of universal vaccination.