The use of _vaccines_ has been tried. In 1918 it was almost universally begun too late—after the epidemic had become prevalent. Prophylactic vaccination should be inaugurated before the disease actually becomes epidemic. Vaccination, particularly against the secondary invaders, is entirely rational. It may not prevent influenza, but it may protect against the serious complications in individuals and may prevent to an extent the spread of secondary invaders in the community. Greenwood aptly remarks that, “In estimating the total effects produced upon morbidity and mortality by disease, the non-specific secondary invaders are as important as the specific causes. The camp followers of an army may do more damage than the regular soldiers, and the same camp followers may ravage in the wake of different armies.” At a conference held at the London War Office, October 14, 1918, the subject of vaccination for influenza was discussed. It was decided that only three organisms should be employed in each case in the preparation of the vaccine; that these races should be recently isolated from cases of the disease developing during the course of the epidemic and that the microorganisms should be submitted to a rigorous study as to race and type. The first dose should include 30,000,000 of Bacillus influenzae, 100,000,000 pneumococcus, 40,000,000 streptococcus; the second dose 60,000,000 Bacillus influenzae, 200,000,000 pneumonococcus, 50,000,000 streptococcus. The vaccine should be sterilized at 55° C. and one-half per cent. phenol should be added. The administration should be at ten days’ intervals. In the United States the vaccines employed have often contained a greater variety of organisms. It is unnecessary to enumerate the results obtained by various investigators. Some have been mildly enthusiastic, while others have obtained no demonstrable benefit. It will suffice to say that there has been no clear evidence that vaccination has been beneficial, but that the procedure has not been given a thorough trial. If the causative organism of the disease is eventually determined, vaccination will probably be attempted with it as antigen. For the success of vaccination it is important that practically entire communities be inoculated, and that they be so inoculated before the development of epidemic prevalence. _Palliative measures in the presence of an epidemic._—An epidemic, once having obtained a start will run its course. Our attempts will be to lessen its extent and diminish its explosiveness. Or, more probably, we will best succeed by _extending_ the duration and making the invasion less explosive. We must know of its earliest appearance. _Notification_ must be made by physicians to the health authorities in order that the earliest increase may be detected. This again renders the reporting of the disease at all times an essential feature. The _administrative control_ and the _publicity_ to be given have already been discussed.