A bacteriological paradigm in influenza research in the first half of the twentieth century.

Scholars have argued that the beginning of virology can be dated from the end of the 19th century: the discovery that some infectious agents could pass through ultrafilters produced a criterium to distinguish ultrafilterable viruses from infectious agents that are not filterable, e.g. bacteria. A filterable agent, claimed to be the cause of human influenza, was isolated in 1933. It will be argued in this paper, however, that the influence of a bacteriological paradigm on influenza research in the first half of the twentieth century was very powerful. Until the late 1940s influenza viruses were studied as infectious entities which, although filterable, were conceived of as analogous to bacteria. It was assumed that filterable viruses which infected animals were a kind of ultrabacteria. According to the bacteriological paradigm the assumed dependence of the filterable viruses on living cells was easy to account for. The second half of the 1940s saw the 'modern concept of virus' begin to be applied to the influenza viruses. Influenza vaccinations in 1946 did not appear to provide protection, from which it was concluded that the influenza virus is very variable. Furthermore, in 1946 and 1947 experimental studies were published, which indicated that the influenza virus may go through an eclipse during its multiplication: it disappears as an infectious agent. Viewed from this perspective, it was only by the second half of the 1940s that research on the influenza virus became emancipated from the bacteriological paradigm.