Influenza is news. Each time an influenza epidemic appears on any large scale … and this happens every two or three years anxiety. Memory of the 1918-19 pandemic dies hard, and it is right that it should live, since we do not know what combination of circumstances brought it about, nor whether it will ever occur again. Nevertheless, no subsequent epidemic has been on such a scale or of such severity as to justify comparison with that disaster.
And yet the comparison has been made in some reports even in this year’s mild epidemic, whereas other reports have contained too optimistic views on the prospects for controlling the disease. Such inaccuracies are perhaps inevitable in this age of speed for there is not time to double-check the accuracy of a report of an incident 5000 miles away when the public demands that the news should be on the breakfast table next morning. The objective assessment of new control measures is a slow process requiring years of patient …….observation in which there is no place for impatient enthusiasm.
Three main types of the virus of influenza have so far been discovered. The two most important of them (A and B) comprise several sub-groups, which in the case of virus A may differ so much as to afford little or no protection following infection or vaccination from subsequent infection by a virus of a different sub-group. During an epidemic, the virus breeds true within certain limits; i.e., an outbreak due to one strain of virus A is not related to one due to a different strain,even if it occurs nearby and at about the same time. from time to time new strains appear which may be quite different from previously known strains, both as far as protection by vaccination is concerned, and also in their ability to cause epidemics and to kill.
The consequences of these facts are that epidemiological reports can only be correctly interpreted in terms of laboratory studies of the viruses responsible; that successful vaccination against influenza depends on knowledge of the virus causing the epidemic; and that continuous vigilance is necessary to detect new and potentially dangerous strains at the earliest possible moment.
It was with these facts in mind that in 1947 the Interim Commission of the World Health Organization initiated a world- wide network of influenza laboratories by setting up the World Influenza Centre in London for the study and comparison of strains of virus isolated in different parts of the world. This was a logical development of a similar network previously set-up by the Armed Services Commission of Influenza in the U.S.A. A second reference laboratory in New York, known as the Strain Study Centre for the Americas. is co-ordinating the work in the Americas. The world network now includes 55 laboratories in 44 different countries. Many more laboratories are co-operating informally.
The work of these laboratories continues summer and winter, for new strains may appear during the summer, and the strains causing epidemics during the winter in the southern hemisphere may spread to the northern hemisphere to cause outbreaks there a few months later. This apparently occurred during the 1950-51 outbreak, when a strain of A-prime virus isolated in South Africa and Australia during June was found to be identical with one causing a severe outbreak in Liverpool in the following January. This became known as the Liverpool subtype; another simultaneously present in Western Europe was called the Scandinavian subtype.
In the latter half of December, 1952, influenza was reported in the U.S.A. in the State of Missouri, the virus being similar to Scandinavian A-prime virus. Numerous reports from other states followed, indicating that the outbreak was widespread in many parts of the country, particularly the central part, but that every-where the disease was mild. Numerous isolations of virus throughout the country confirmed that an A-prime virus was responsible for the outbreak, although, as is frequently the case, a few sporadic cases of influenza B were detected. The epidemics continued to increase during the first three weeks of January, with a small increase in the number of deaths attributed to influenza and pneumonia. Towards the end of January, there were indications that in some states at least the epidemic had reached its peak.
Unfortunately, vaccination against influenza produces neither as lasting nor as complete an immunity as does, for example, vaccination against smallpox. In controlled trials in the past, the unprotected individuals have been attacked about four times as often as the inoculated, but a number of the latter still become ill with the disease, and the degree of protection has probably waned considerably after a year.
It must be stressed that the vaccines at present under test lend no hope of being able to eliminate the disease; the best can be hoped for is to limit the effects of an epidemic by reducing the number of people who fall sick, hence diminishing the economic effects of the epidemic which are sometimes serious. All claims of the successful control of influenza must be interpreted in this strictly limited sense. If by control measures the effect of an epidemic of influenza could be reduced throughout a country to one-tenth of what it would otherwise be, that would indeed be a success. It cannot be achieved at present. There are several difficult problems which must be solved first.
Primarily there is the unpredictability of the influenza virus, which shows no stability in nature. This is being tackled by an “intelligence service” which is constantly studying changes in the virus; this may eventually lead to the ability to forecast epidemics with reasonable reliability.
Further, a great deal remains to be learned about the best methods of producing, testing and using vaccines. There is, for example, a relatively new type of vaccine under test which appears to have advantages in the degree and duration of immunity produced, together with economy in the amount of virus needed. There is no doubt that, if this is confirmed and the safety of the vaccine proven, it will represent a major advance.
The use of influenza vaccines presents a number of problems. It is clearly impracticable to vaccinate the whole population each year, owing to the great expense and difficulties of such a scheme. The questions are whom to inoculate and when. The answers will depend a great deal on local conditions and economy. It is hoped that some guidance on this will be forthcoming, as a result of the trials at present in progress. GENEVA, SWITZERLAND.