It was clarified that a culture of a propionic acid bacterium exhibited a prophylactic effect on influenza infection. Disclosed is a composition comprising a culture of a propionic acid bacterium which is capable of potentiating the induction of a neutralizing antibody in an animal that has been inoculated with an influenza vaccine. The fact that the component constituting the aforesaid composition has been eaten by humans over a long time assures the high safety and good taste thereof and, therefore, said composition can be taken over a long period of time. In addition, the aforesaid composition can contain, as optional components, a milk fermentation product and an oligosaccharide. It can be also expected that another effect of controlling the functions of the intestines is achieved by administering the aforesaid composition.
