The infant mortality rate (IMR) refers to the number of infants who die before reaching their first birthday, measured annually. This rate is a crucial measure of infant health globally and serves as a strong indicator of the overall quality of healthcare systems. Historically, infant mortality rates were very high, primarily due to poor access to medical care, inadequate sanitation, and limited understanding of disease prevention. However, starting in the early 1900s, industrialized nations saw significant declines in IMR thanks to improvements in healthcare and the introduction of public health initiatives. By the 2000s, further reductions were achieved with the introduction of new vaccines and large-scale immunization programs. In high-income countries like the USA, Canada, and Sweden, the IMR is typically around 4 to 5 deaths per 1,000 live births, whereas in low-income countries such as Somalia and Niger, the rate remains much higher, at approximately 50 to 60 deaths per 1,000 live births.