In the earlier influenza epidemics we know that, as a rule, after intervals of several months or longer, epidemic outbreaks of more or less extensive geographic distribution follow the first great pestilence.
Obviously, therefore, the epidemic of 1729-1730 has some relation to the outbreak of the pestilence in 1732 and 1733. The great pandemic of 1782 most likely had genetic forerunners in the years 1780 and 1781. The epidemic of 1788 continued with intervals to the year 1800, and perhaps stands in direct connection with the epidemics of 1802,1803,1805, and 1806.
Of especial interest is the pandemic pestilence of 1830, which continued into the years 1831 and 1832. In 1833 a second pandemic invasion occurred again, starting from Russia. The epidemic of the years 1836 and 1837 had trailers until 1838 and 1841. The epidemic of 1847 and 1848 recurred at intervals until the year 1851. History teaches us then that influenza periods often last for several years, and have frequently long intervals of time between the separate endemic epidemic portions.
After the disappearance of our latest pandemic many thought, without reflecting upon the lessons of history, that the epidemic form of the disease would slumber once more for decads until a new pandemic analogous to the one through which they had just passed should attract the attention of later generations.
The cases of influenza which everywhere arose sporadically in the course of the year 1890 remained isolated, or at the most formed a small epidemic. Only in a few districts of Europe (i. e., Lisbon, Nuremberg, Paris, Copenhagen, Edinburgh, Riga, London, Funfkirchen, and Detmold) did a few recurrent epidemics take place in the year 1890; but in Japan only, in August, 1890, was there a marked recurrence. These are easily explained as arising from the residual germs of the pandemic.
Only one year after the end of the great epidemic influenza reappeared. In January and February, 1891, there were marked epidemic outbreaks in Buenos Aires and Chile, but particularly in North America (New Orleans, Chicago, Washington, Boston, San Francisco, etc.), and simultaneously in the north of England (Durham, North Yorkshire, Abertillery, etc.). In both countries a further distribution of the pestilence took place during the months of March and April, New York being affected in the third week of March and London not until the beginning of May. In May, too, there were epidemics in Sweden and Norway, and in Denmark during June.
In spite of these facts the simultaneous North American and English epidemics were considered by some to be one and the same, but also to have given rise, as centers of infection, to the entirely isolated local epidemics which arose during April in Portugal, southern Russia, and Poland; in June, in Egypt; in August, in St. Petersburg, which they regarded as terminal trailers of the Anglo-American epidemic. All these opinions are purely imaginary products and lack any foundation in fact. Parsons already rejected the idea that the English spring epidemic of 1891 arose from the coexisting American one. In this he was justified, for a glance at the mode of distribution in England shows that influenza first occurred upon the northeastern coast, in rural districts and cities of the interior which had no direct means of communication with North America. Even assuming that the pestilence was imported from America to England, why was it not also brought to Germany, Holland, Belgium, and France? Not one instance can be found of the introduction of the disease from highly infected England into Germany, not even during May, the principal month of travel, at which time the epidemic had reached its acme in in London.
A. Netter describes the character of these successive epidemics with the words, "The grippe occurred in simultaneous or successive outbreaks, and one could not classify in any manner the various foci, as had been possible during 1889-1890. Very likely there were recurrent outbreaks of the epidemic at various places."
Shipping also, which in the pandemic of 1889-1890 played so very important a role in the dissemination of the pest over the earth, proved, in the spring of 1891, to be absolutely without influence in spite of the fact that the chief maritime country, England, was then the hotbed of influenza. In order to explain this immunity of the European continent refuge was taken in the expression " alternating national immunity." Because England had escaped so easily (?) in 1889-1890, she was less immune to the germs introduced from America in the spring of 1891.
Is it probable that the German, French, and other nations at that time were more immune than the Americans and English?
In this first epidemic reappearance of influenza after the pandemic we find the epidemiologic character of the disease markedly altered, and this change in character becomes more striking if we glance for a short time at the later epidemics.
The third tremendous epidemic dissemination of influenza, a true pandemic, began in the fall (October) of 1891 and continued during the entire winter, up to the spring of 1892. It prevailed most extensively over the whole of Europe and North America, but was also noticed during this period in all other parts of the world: in Africa (Egypt, Sierra Leone), in the Azores, Samoa, in Havana, in Persia, China, Japan, in Australia (Melbourne, Sydney), etc.
The following are briefly the most important peculiarities of the two epidemics of the spring of 1891 and the great winter epidemic of 1891-1892. The geographic manner of distribution no longer conforms to any rule-the origin is not from a single center (as in Russia in 1889); there is no continuous progress along trade routes. The law observed in the pandemic, that the large cities and commercial centers are attacked earlier than the open country and places situated on the principal highways (railroads, harbors) earlier than isolated or inland towns, does not hold good in the later epidemics.