During the interwar period, Lwów held the rank of the Second Polish Republic's third most populous city (following Warsaw and Łódź), and it became the seat of the Lwów Voivodeship. Following Warsaw, Lwów was the second most important cultural and academic centre of interwar Poland. For example, in 1920 professor Rudolf Weigl of the Lwów University developed a vaccine against typhus fever. Furthermore, the geographic location of Lwów gave it an important role in stimulating international trade and fostering the city's and Poland's economic development. A major trade fair called "Targi Wschodnie" was established in 1921. In the academic year 1937–1938, there were 9,100 students attending five institutions of higher education, including the Lwów University as well as the Polytechnic.