ABSTRACT
BACKGROUND: In 2007 universal vaccination against chicken pox was introduced in the vaccine calendar of Navarre. The aim of this study is to evaluate the impact of this measure on the incidence of chicken pox in both the vaccinated cohorts (direct effect) and in the unvaccinated cohorts (indirect effect). MATERIAL AND METHODS: Chicken pox is a disease of individualized compulsory notification. We analyzed the annual incidence by age groups between 2006 and 2010. Hospital admittances with chicken pox or complicated chicken pox as the principal diagnosis were taken from the minimum basic data set on hospital discharges for the years 2006 to 2009. RESULTS: The incidence of chicken pox has fallen by 93.0%, from 8.04 cases per 1,000 inhabitants in 2006 to 0.56 per 1,000 inhabitants in 2010 (p<0,0001). In children from 1 to 6 years (vaccinated cohorts), the incidence of chicken pox has fallen by 96.3%. In the cohorts vaccinated at 10 and 14 years, a fall of 93.6% can also be observed in children from 10 to 14 years, and of 85.0% in those of 15 to 19 years. In the unvaccinated age groups we can observe falls of 88.2% in children under one year, of 73.3% in those of 7 to 9 years, and of 84.6% in people over 20 years. In 2006 there were 25 hospital admissions due to chicken pox in Navarre and in 2009 this figure fell to 7. The rate of admissions fell by 71%. CONCLUSION: The introduction of universal chicken pox vaccination in Navarre has resulted in a rapid and very steep reduction of the incidence of chicken pox in both vaccinated and unvaccinated people.
