In 1900, the smallpox vaccine was the only one administered to children. By the early 1950s, children routinely received three vaccines, for protection against diphtheria , pertussis , tetanus and smallpox , and as many as five shots by two years of age.  Since the mid-1980s, many vaccines have been added to the schedule. As of 2009 [update] , the US Centers for Disease Control and Prevention (CDC) now recommends vaccination against at least fourteen diseases. By two years of age, . children receive as many as 24 vaccine injections, and might receive up to five shots during one visit to the doctor.  The use of combination vaccine products means that, as of 2013 [update] , the United Kingdom 's immunization program consists of 9 injections by the age of two, rather than 22 if vaccination for each disease was given as a separate injection. 
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