Published: 8 December 2016
Prescriber Update 37(4): 56-57
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 Zealand4,5. 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:
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).
|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.