Influenza

by Warren T. Vaughan

Measles.—A comparison of influenza and measles will offer some explanation of the differences between the epidemic constitution of the former and that of the other respiratory diseases.

We are accustomed to think of measles as a disease which, like meningitis, is disseminated throughout the civilized world, and which although constantly with us causes only sporadic cases. True epidemics of measles do occur, even when there is no gross change in the constitution of the population. We have discussed examples of this particularly in London. Flare-ups of measles prevalence are in fact so much the rule that in certain localities health officers anticipate a measles epidemic about once in two years. Furthermore measles has been known more than once to occur in extensive epidemic form, attacking large proportions of the population invaded. We know that there is an immunity to measles which is nearly absolute in those who have once acquired the disease. The epidemics have, therefore, occurred exclusively in those localities where the proportion of immune individuals was relatively small. According to Noah Webster in 1772 measles appeared in all parts of America and was accompanied by an unusually high mortality. In Charleston 800 or 900 children died of the disease. The following year measles “finished its course and was followed by a disorder of the throat.”

In 1781 measles disappeared from the Faroe Islands, and for the following sixty-five years there was not a case of this disease anywhere on any of the seventeen islands constituting the inhabited parts of this group. When the disease was finally re-introduced into these islands, it spread throughout the population, attacking practically every individual in a relatively short interval of time, showing a much higher attack rate than did influenza in 1918. There was this difference, that the only individuals who did not acquire measles on its re-introduction into the islands were those who had had it sixty-five years before. Panum did not find an authentic case of recurrence in the same individual. There was not a single instance of second attack of measles, although the shortest possible interval between the previous attack and the subsequent exposure was sixty-five years.

In 1875 measles first reached the inhabitants of the Fiji Islands. The disease was introduced by the King of the Fiji Islanders and his escort, upon their return from New South Wales. The entire population of the islands was estimated at 150,000 and it is officially stated that there were 40,000 deaths from measles in the ensuing period. In certain islands and villages where more exact information was secured, it was found that from twenty-seven to twenty-eight per cent. of the people died. Panic, insanitary conditions and ignorance of how to care for the sick resulted in this high mortality. V. C. Vaughan has remarked that when measles is introduced into a population with a susceptibility of 100 per cent. “it strikes down so many at practically the same time that adequate care for the sick is impossible.” The rapidity with which the population is invaded is practically as great as it is during influenza epidemics.

It is the opinion of the author that the phenomenon which contributes chiefly to the occurrence of influenza in epidemics and pandemics, and which causes the characteristic curves of a primary influenza wave, is the absence of any permanent immunity. We have shown in our discussion that no immunity is proven to exist after a year and a half or two years at the most. Measles occurring in a non-immune population spreads through that population with the same high rate as does the influenza. In Charts XXVIII and XXIX we find the curves of incidence of measles in certain of the United States Army camps in the fall and winter of 1917–18. The simplest curve is that for Camp Wheeler. Here the type is similar to that found in the primary wave of influenza. There is a quasi-symmetrical evolution and the concentration is closely grouped around the maximum. The total duration of the epidemic is short, not being much over eight weeks. The troops at this camp were predominantly rural. The disease starting in this group of relatively non-immunes spread rapidly until presumably all susceptible material was exhausted. Compare Camp Wheeler with those camps where the population was chiefly urban. Here the wave is of longer duration, is not as high, the increase is slower, the decrease is more gradual and the concentration is not grouped so closely about the maximum. In the case of the other camps with chiefly rural population, the curve is not as simple as is the case with Camp Wheeler, and there are at times secondary curves as in the case of Camp Bowie, but the essential similarity to the curve at Camp Wheeler and the difference from the curves at Devens, Dix, Custer and Grant is striking. It may be that the double waves are explained by acquisition of new bodies of troops, by the introduction of new susceptible material. On this question we have no exact information.

CHART XXVIII.

CHART XXIX.

This experience was equally true during the Civil war. Although there are no exact reports, it appears that measles prevailed in the Confederate army and was much more highly fatal than in the Union army.