This is a timeline of the development of prophylactic human vaccines. Early vaccines may be listed by the first year of development or testing, but later entries usually show the year the vaccine finished trials and became available on the market. Although vaccines exist for the diseases listed below, only smallpox has been eliminated worldwide. The other vaccine-preventable illnesses continue to cause millions of deaths each year. Currently, polio and measles are the targets of active worldwide eradication campaigns.