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. 2011 Jan 26;6(1):e16363.
doi: 10.1371/journal.pone.0016363.

Sudden unexpected deaths and vaccinations during the first two years of life in Italy: a case series study

Giuseppe Traversa  1 , Stefania Spila-Alegiani, Clara Bianchi, Marta Ciofi degli Atti, Luisa Frova, Marco Massari, Roberto Raschetti, Stefania Salmaso, Gianpaolo Scalia Tomba; Hera Study Group
Collaborators, Affiliations

Sudden unexpected deaths and vaccinations during the first two years of life in Italy: a case series study

Giuseppe Traversa et al. PLoS One. .

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.

Methodology/principal findings: 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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Description of the observation period for a hypothetical subject included in the study.
Legend A. Self-controlled case-series method for censoring, perturbed or curtailed post-event exposures Legend B. Poisson regression model.
Figure 2
Figure 2. Selection of the study population, age 31–729 days, Italy 1999–2004.
Legend. *One subject was excluded because the date of birth was unknown.
Figure 3
Figure 3. Distribution of the 604 events of SUD included in the study by age of death.
Legend. The three arrows indicate the median age at first, second and third vaccine dose.
Figure 4
Figure 4. Distribution of immunised subjects by interval between date of vaccination and date of death.
* Legend. *Only events occurring within 45 days from vaccination are shown.
See this image and copyright information in PMC

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