In 1951 this figure had fallen to less than one in thirty and by 1994 less than one in a hundred under-fives failed to survive. However, there is no doubt that improved healthcare has played a major role in this dramatic change, as it has in prolonging life expectancy amongst the elderly. A striking example of the effects of improved healthcare on childhood mortality is its impact on the incidence of fatal infectious diseases. In the middle of the last century infectious diseases accounted for sixty percent of deaths in children between the ages of one and fourteen. Deaths from infections in this age group fell from more than one thousand per million in 1911 to about eleven per million in 1991.
Most infant mortality resulting from infections occurs in the first year of life.
The reason for this is that the cells of the body which fight infection, collectively called the immune system, are not fully developed in young infants, rendering them susceptible to a variety of microbes which are more or less innocuous to adults. The recognition of this fact was a major stimulus for the development of vaccines to a variety of childhood infections. Vaccines are, broadly speaking, either innocuous extracts of the infectious microbe, or an inactivated form of the microbe, which provoke immune responses that serve to curtail future infections with that organism. The introduction of mass vaccination to these childhood infections has had a huge impact on childrens health and has led essentially to complete eradication of some of these diseases in the Western world. In addition, many of the common causes of bacterial infections of children can be treated with antibiotics, which has also had a major influence on the incidence of serious infectious illness in this age group.