1793 Philadelphia yellow fever epidemic the origin of the fever nor that it was transmitted by mosquitoes (which was not verified until the late nineteenth century). The mayor and a committee of two dozen organized a fever hospital at Bush Hill and other crisis measures. The assistance of the Free African Society was requested by the city and readily agreed to by the members, based on the mistaken assumption that native Africans would have the same partial immunity to the new disease as many had to malaria, the most common source of fever epidemics during the summer months. Black nurses aided the sick and the
Yellow fever 10 years. Although the WHO on 17 May 2013 advised that subsequent booster vaccinations are unnecessary, an older (than 10 years) certificate may not be acceptable at all border posts in all affected countries. A list of the countries that require yellow fever vaccination is published by the WHO. If the vaccination cannot be conducted for some reasons, dispensation may be possible. In this case, an exemption certificate issued by a WHO-approved vaccination center is required. Although 32 of 44 countries where yellow fever occurs endemically do have vaccination programmes, in many of these countries, less than 50% of their