Published: 8 December 2016

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Sudden Unexpected Death in Infants (SUDI): No Causal Link to Vaccination

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Prescriber Update 37(4): 56-57
December 2016

Sudden unexpected death in infants (SUDI), also known as sudden infant death syndrome (SIDS) or cot death, continues to be a leading cause of death in infants worldwide¹. SUDI is defined as the sudden unexpected death of an infant <1 year of age, with the onset of the fatal episode apparently occurring during sleep that remains unexplained after a thorough investigation including performance of a complete autopsy and review of the circumstances of death and the clinical history².

A number of risk factors for SUDI have been identified. The Ministry of Health provides advice on safe sleep practices to reduce the risk of SUDI³. In the general population, there is concern that an increased risk of SUDI occurs after vaccination, but is this warranted?

Data on infant deaths are published by the Ministry of Health and Statistics New Zealand^4,5. The latest data published by the Ministry of Health is for 2012. In 2012 the infant mortality rate was 4.7 per 1000 live births per year (total of 294 infant deaths). The rate of SUDI was 0.6 per 1000 live births per year (total of 36 cases)⁶.

Using the 2012 figures for SUDI, around three cases are expected per month. Infants are given three sets of vaccines in the first year of life, at 6 weeks, 3 months and 5 months. Therefore, up to nine reports of cases of SUDI occurring within a month of vaccination may be expected each year through chance alone. This is an estimate because not all children are vaccinated, and the risk of SUDI varies, with the peak incidence being at two to three months². Furthermore, the number of SUDI cases in New Zealand is small and rates may fluctuate from year to year⁶.

On average, the Centre for Adverse Reactions Monitoring (CARM) receives two to four cases of infant death after vaccination each year. Reporters do not necessarily think that there is a link between the death and vaccination but wish to record the event in the national database. In these cases, the time period between vaccination and the death has been reported at less than 12 hours and up to 30 days. The infants in the reports were aged between 6 weeks and 25 weeks.

It should be noted that cases are often reported to CARM before the coronial investigation, and therefore in some cases, a cause of death may be ascertained later. CARM encourages reporters to send further information on these cases but acknowledges that this may not always be available to the reporter. Other risk factors for SUDI such as parental smoking are rarely described in the CARM reports.

A number of observational studies have investigated a possible link between vaccination and SUDI. There are some limitations to these studies such as:

• the healthy vaccinee effect (whereby sick children who may be more at risk of SUDI are not vaccinated)
• the difficulty of identifying unvaccinated controls
• the difficulty of verifying that the death was due to SUDI
• the inability to fully control for other risk factors such as age
• the concurrent timing of campaigns to promote safe infant sleeping practices with the initiation of vaccination programmes.

Although the suspicion of a possible association between the newer hexavalent vaccines was raised by a German group based on three cases⁷, observational studies have failed to find a causal link, or have in fact found that vaccination reduced the risk of SUDI (Table 1).

Table 1: Summary of more recently published observational studies of sudden infant death syndrome following vaccination. [This is not a comprehensive summary of all studies published on this topic]

Study	Dates	Data source	Number of subjects	Analysis	Results	Conclusions
Mueller- Nordhorn1	1968–2009	Centers for Disease Control in the US, US Immunisation Survey, National Infant Sleep Position Survey.	US population-wide.	Poisson regression model (ecological study).	IRR 0.92 (0.87–0.97) per 10% increase in DTP immunisation coverage after adjusting for infant sleep position.	Increased DTP immunisation coverage was associated with decreased SIDS mortality.
Traversa8	1999–2004	Population of children resident in Italy, cases identified through death certificates.	604 cases of sudden unexplained death.	Self-controlled case series methodology.	A limited increase in risk after the first dose of hexavalent vaccine only RR: 2.0 (1.2–3.5).	The limited increase after the first dose may be partly explained by residual uncontrolled confounding effect of age.
Kuhnert9	1987–2001	Reanalysis of German study on sudden infant death (GeSID), the confidential enquiry into still births and deaths in infancy (CESDI) study and the New Zealand cot death study (NZCD).	GeSID-333 cases and three controls per case CESDI – 154 cases and up to four controls per case NZCD – 393 cases.	Case-control and self- controlled case series models were used to re- analyse the data.	Numerous outcomes showing no difference between vaccinated and non- vaccinated subjects.	No increase or decrease in SIDS associated with vaccination.

IRR, incidence rate ratio; RR, rate ratio; DTP, Diphtheria-Tetanus-Pertussis

In conclusion, the available evidence continues to show no causal link between vaccination (immunisation) and SUDI.

Please continue to report all adverse events following immunisation to CARM (https://nzphvc.otago.ac.nz/). Recording these cases in the national database enables the event to be reviewed and the quality and safety of vaccines to be monitored.

References

1. Mueller-Nordhorn J, Hettler-Chen C, Keil T, et al. 2015. Association between sudden infant death syndrome and diphtheria-tetanus-pertussis immunisation: an ecological study. BMC Pediatrics 15(1): 1-8.
2. Brotherton JML, Hull BP, Hayden A, et al. 2005. Probability of coincident vaccination in the 24 or 48 hours preceding sudden infant death syndrome death in Australia. Pediatrics 115(6): e643-646.
3. Ministry of Health. 2015. Safe sleep. 27 August 2015. URL: www.health. govt.nz/your-health/pregnancy-and-kids/first-year/helpful-advice-during-first-year/safe-sleep?icn=promo-1styear&ici=safesleep (accessed 10 October 2016).
4. Ministry of Health. 2014. Fetal and infant deaths – series. 15 July 2014. URL: www.health.govt.nz/nz-health-statistics/health-statistics-and-data-sets/fetal-and-infant-deaths-series (accessed 10 October 2016).
5. Statistics New Zealand. Births and Deaths – information releases. URL: www.stats.govt.nz/browse_for_stats/population/births/info-releases.aspx (accessed 10 October 2016).
6. Ministry of Health. 2015. Fetal and Infant deaths 2012. 19 August 2015. URL: www.health.govt.nz/publication/fetal-and-infant-deaths-2012 (accessed 16 September 2016).
7. Von Kries R, Toschke AM, Strassburger, et al. 2005. Sudden and unexpected deaths after the administration of hexavalent vaccines (diphtheria, tetanus, pertussis, poliomyelitis, hepatitis B, Haemophilius influenzae type b): is there a signal. European Journal of Pediatrics 164(2): 61-69.
8. Traversa G, Spila-Alegiani S, Bianchi C, et al. 2011. Sudden unexpected deaths and vaccinations during the first two years of life in Italy: a case series study. PLoS ONE 6(1): e16363.
9. Kuhnert R, Schlaud M, Poethko-Mueller C, et al. 2012. Reanalyses of case-control studies examining the temporal association between sudden infant death syndrome and vaccination. Vaccine 30(13): 2349-2356.