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On April 7, 1948, the World Health Organization was formed by the United Nations. From the article:

"Origin and development of health cooperation
International health cooperation began with the first International Sanitary Conference in Paris, which opened on 23 July 1851. The objective of this conference was to harmonize and reduce to a safe minimum the conflicting and costly maritime quarantine requirements of different European nations.

The first international sanitary convention, addressing cholera, was ratified and came into force at the seventh International Sanitary Conference in Venice in 1892. Further conferences in Dresden in 1893 and Paris in 1894 resulted in two additional conventions relating to cholera. The next conference in Venice in 1897 adopted a new international convention dealing with prevention of the spread of plague. All four of these conventions were consolidated into a single International Sanitary Convention in 1903.

At the 1903 conference it was agreed in principle that a permanent international health bureau should be established. At that time, the American republics had already established the International Sanitary Bureau in 1902 in Washington- later renamed the Pan American Sanitary Bureau.

At a meeting of government representatives in Rome in 1907 the final decision was taken to establish an Office international d'Hygiène publique (OIHP) in Paris, with a permanent secretariat and a "permanent committee" of senior public health officials of member governments. This committee first met towards the end of 1908 and thereafter twice a year, except during the First World War.

The League of Nations was created as an aftermath of the First World War. One of its tasks was to "endeavour to take steps in matters of international concern for the prevention and control of disease". All existing international bureaux were to be placed under the direction of the League. It was assumed that the OIHP would be incorporated within the administrative framework of the League; however, at the last moment, the USA, which was a member of the OIHP but not of the League, vetoed this fusion. Thus, in the years between the two World Wars, two independent international health organizations co-existed in Europe - the OIHP and the Health Organisation of the League of Nations. These two organizations consulted and cooperated with one another, along with the Pan American Sanitary Organization (now the Pan-American Health Organization).

With the outbreak of the Second World War, international health work came almost to a standstill.

In April 1945, during the Conference to set up the United Nations (UN) held in San Francisco, representatives of Brazil and China proposed that an international health organization be established and a conference to frame its constitution convened. On 15 February 1946, the Economic and Social Council of the UN instructed the Secretary- General to convoke such a conference. A Technical Preparatory Committee met in Paris from 18 March to 5 April 1946 and drew up proposals for the Constitution which were presented to the International Health Conference in New York City between 19 June and 22 July 1946. On the basis of these proposals, the Conference drafted and adopted the Constitution of the World Health Organization, signed 22 July 1946 by representatives of 51 Members of the UN and of 10 other nations. The Conference established also an Interim Commission to carry out certain activities of the existing health institutions until the entry into force of the Constitution of the World Health Organization.

The preamble and Article 69 of the Constitution of WHO provide that WHO should be a specialized agency of the UN. Article 80 provides that the Constitution would come into force when 26 members of the United Nations had ratified it.

The Constitution did not come into force until 7 April 1948, when the 26th of the 61 governments who had signed it ratified its signature. To bridge the gap, the Interim Commission continued the work previously undertaken by the Health Organisation of the League and the OIHP. For several years, the Health Division of the United Nations Relief and Rehabilitation Administration (UNRRA) and the Interim Commission of WHO took over responsibility for the international sanitary conventions and for international epidemiological reporting, The first Health Assembly opened in Geneva on 24 June 1948 with delegations from 53 of the 55 Member States. It decided that the Interim Commission was to cease to exist at midnight on 31 August 1948, to be immediately succeeded by WHO."