Sudden Infant Death Syndrome (SIDS) is the sudden death of an infant under one year of age that remains unexplained after the performance of an complete investigation, including an autopsy, and examination of the scene of death, and a review of the case history. SIDS occurs during an infant's sleep, either nighttime or naptime. Ninety percent of SIDS cases occur by six months of age. Most SIDS cases occur between two and four months of age. SIDS does occur below the age of one month and past six months, but is uncommon. Most SIDS infants are discovered between 10:00 P.M. and 10:00 A.M. The peak hour seems to be around 5:00 A.M. Also SIDS is more likely to occur on weekends and holidays and during the cold weather months. SIDS is the leading cause of death in infants between one month and one year, accounting for approximately forty percent of infant deaths in the United States (Sears 15). For unknown reasons, SIDS is higher in males than in females, by a ratio of 1.5 to 1. The increased incidence of SIDS among African Americans than among Caucasians is thought to be more likely the result in different childcare practices, education, and socioeconomics than race itself. .
Immunizations do not cause SIDS. Statements implicating immunizations as a causing factor for SIDS is unproved and false. The cause for this unfortunate bad press is coincidental: the peak period of SIDS (which is the colder months) occurs at the same time that babies get there shots. While many babies dying of SIDS have no previous warning signs or risk factors, some infants seem to be at higher risk than others. The term "risk factor" refers to some element in the baby's environment or development that increases the chances of dying of SIDS (Sears 17). For example infant's whose mothers smoke prenatal or postnatal have higher risk of dying of SIDS than babies of mothers whom do not smoke (Sears 18). This does not mean that SIDS is common among children of smokers.