title: Sudden unexpected deaths and vaccinations during the first two years of life in Italy: a case series study.
abstract: BACKGROUND
  The signal of an association between vaccination in the second year of life with a hexavalent vaccine and sudden unexpected deaths (SUD) in the two days following vaccination was reported in Germany in 2003. A study to establish whether the immunisation with hexavalent vaccines increased the short term risk of SUD in infants was conducted in Italy.
  
  
  RESULTS
  The reference population comprises around 3 million infants vaccinated in Italy in the study period 1999-2004 (1.5 million received hexavalent vaccines). Events of SUD in infants aged 1-23 months were identified through the death certificates. Vaccination history was retrieved from immunisation registries. Association between immunisation and death was assessed adopting a case series design focusing on the risk periods 0-1, 0-7, and 0-14 days after immunisation. Among the 604 infants who died of SUD, 244 (40%) had received at least one vaccination. Four deaths occurred within two days from vaccination with the hexavalent vaccines (RR = 1.5; 95% CI 0.6 to 4.2). The RRs for the risk periods 0-7 and 0-14 were 2.0 (95% CI 1.2 to 3.5) and 1.5 (95% CI 0.9 to 2.4). The increased risk was limited to the first dose (RR = 2.2; 95% CI 1.1 to 4.4), whereas no increase was observed for the second and third doses combined.
  
  
  CONCLUSIONS
  The RRs of SUD for any vaccines and any risk periods, even when greater than 1, were almost an order of magnitude lower than the estimates in Germany. The limited increase in RRs found in Italy appears confined to the first dose and may be partly explained by a residual uncontrolled confounding effect of age.
authors.affiliation: National Centre for Epidemiology, Surveillance and Health Promotion, National Institute of Health, Rome, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Traversa
authors.forename: Stefania
authors.initials: S
authors.lastname: Spila-Alegiani
authors.forename: Clara
authors.initials: C
authors.lastname: Bianchi
authors.forename: Marta
authors.initials: M
authors.lastname: Ciofi degli Atti
authors.forename: Luisa
authors.initials: L
authors.lastname: Frova
authors.forename: Marco
authors.initials: M
authors.lastname: Massari
authors.forename: Roberto
authors.initials: R
authors.lastname: Raschetti
authors.forename: Stefania
authors.initials: S
authors.lastname: Salmaso
authors.forename: Gianpaolo
authors.initials: G
authors.lastname: Scalia Tomba
mesh_terms: D000367:Age Factors; D003625:Data Collection; D003627:Data Interpretation, Statistical; D003645:Death, Sudden / Q000453:epidemiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007558:Italy / Q000453:epidemiology; D012306:Risk; D014611:Vaccination / Q000401:mortality*