Was Aldo Castellani the inventor of combined and polyvalent vaccines?

Italian born and long term resident in England, Sir Aldo Castellani (1874-1971), is usually credited with "several discoveries of great importance in tropical medicine", most notably for his role in determining the aetiology of sleeping sickness and yaws. This contribution tries to highlight his role in the history of vaccinology as a pioneer in the design and use of combined and polyvalent vaccines. In the light of existing data, while acting as Director of the Bacteriological Institute of Colombo (Ceylon) in the decade before the First World War, Castellani was the first to experiment with both different strains of "antigens belonging to the same group" like in his typhoid-paratyphoid vaccine (TAB), as well as the simultaneous use of more pathogens, or part of them, for protection against different diseases, like in his "tetravaccine" (TAB + cholera) and "pentavaccine" (TAB + cholera + Malta fever). At the beginning of the War, based on the results of thousands of vaccinations, he strongly maintained that those combined or mixed vaccines were harmless and effective. The Allied Armies became more and more interested in Castellani's methods. His TAB vaccine was extensively used among the soldiers and his contributions were largely acknowledged especially in the Anglo-Saxon world in the following years, when it was plainly stated that "to Castellani is due the credit of having first proposed, prepared, and used, combined vaccines". The path to widespread use of combination and polyvalent vaccines - which is usually dated back only to the late 1940s - was still long and winding. Castellani himself abandoned that field of research after the War and this is probably why that early history is nowadays often forgotten.