Vaccines administered in infancy cause Sudden Infant Death Syndrome.
The temporal clustering of infant vaccinations in the first year of life coincides with the peak age for SIDS (2-4 months), creating a misleading association. However, rigorous epidemiological studies have consistently shown that vaccination does not increase SIDS risk; indeed, SIDS rates have declined since the 1990s as vaccination coverage improved. A large Danish study of over 400,000 infants found that vaccinated infants actually had a lower SIDS risk than unvaccinated infants. The cause of SIDS remains multifactorial and largely unexplained, but involves sleep position, bedding materials, and possibly undetected metabolic or cardiac conditions, nothing mechanistically related to vaccine ingredients or immune responses. The 'temporal clustering' bias is a critical reminder that correlation in timing is not causation, and one of the most important lessons in epidemiology.