There are no exact statistics on the subject, but it is a safe assumption that a majority of historians of medicine work on the 19th century. It is thus rather surprising that the most recent synthetic full-length study of the development of modern medicine by a professional medical historian was Richard Shryock's The Development of Modern Medicine, first published in 1937. The reason, one suspects, is that historians initially had little to add to received views on the subject.
In more recent years, the reverse is true. There is a wealth of recent monographic research in the field, ranging from conventional history of scientific ideas to social and cultural history and extending as well to demography. It is hard to control so much disparate material and even more difficult to give it coherent narrative form.
In this excellent synthetic study, William Bynum of the Wellcome Institute in London has dealt