Influenza in the USSR in 1977: recurrence of influenzavirus A subtype H1N1.

Early in November 1977, several outbreaks of influenza were reported in the far eastern region of the USSR. The epidemic spread rapidly throughout the country affecting mainly people under the age of 20 years. Most of the strains of virus isolated were found to be influenza A subtype H1N1. The serological characterization of the strains is described in this paper.

Comparison of influenza viruses isolated from man and from whales.

Four isolates of influenza virus strains from Moscow and Habarovsk that caused outbreaks of influenza in November and December 1977 in several cities of the USSR were studied and their haemagglutinins and neuraminidases were compared with those of other human and animal influenza viruses including A/whale/Pacific Ocean/76. In H1 tests these isolates, designated A/USSR/77, reacted with immune serum against A/FM/1/47 (H1N1) to the homologous titre, and with antiserum against A/whale/PO/19/76 virus to 1/8 of the homologous titre. In neuraminidase inhibition tests all A/USSR/77 isolates showed the presence of human N1 type neuraminidase, more closely related to A/sw/New Jersey/76 (Hsw1N1) than to A/FM/1/47 (H1N1) virus. The haemagglutinin of A/whale/Pacific Ocean/19/76 virus occupies an intermediate position between H0 and H1, but its neuraminidase is close to Nav2. The virus from whales multiplies better at low (28 degrees C) and at high (40 degrees C) temperatures than do the viruses of human origin that were tested.

Influenza A2 and B in the USSR in 1966-67, and some aspects of global epidemiology of influenza.

An epidemic wave of influenza caused by the A2 virus was recorded in the USSR in the winter of 1966-67; this was the fifth wave since this pandemic strain first appeared. In contrast to the last wave of 1965, it developed simultaneously with, or followed, an epidemic of influenza B. The epidemic spread of influenza was observed for a period of 2 years in the USSR; influenza B prevailed in 1966, influenza A2 in 1967, and the two viruses spread at different speeds. A slow spread and a gradual increase in intensity during most of the year was characteristic of influenza B while influenza A2 spread rapidly and involved a considerable part of the country within 3 months.Although the influenza B started to spread almost 9 months before influenza A2 became active, the periods of maximum intensity of both outbreaks coincided in most parts of the USSR in the winter of 1966-67. The approach of summer temporarily stopped the spread of influenza B but did not bring the outbreak to an end nor lessen the intensity of the next wave in the autumn. Among the haemagglutinating agents isolated in the USSR in 1966-67 were 121 strains of virus B and 132 strains of virus A2. A study of the antigenic structure of the B strains showed that they were not all similar; some of them were closely related to B/Johannesburg/33/58, a greater number were more closely related to B/Singapore/3/64 and a number of strains differed from both varieties.Among the A2 viruses isolated and investigated were strains similar to those of pandemic prototype A2/Singapore/1/57, strains close to A2/England/12/64 and A2/USSR, Gor/62/65, strains antigenically different from all those strains but still related to the A2 subtype and strains that had S-antigen of A-type but which were not inhibited by antisera to the prototypes A2/57, A2/64 or A2/67.Outbreaks of influenza A2 and B recorded in the USSR are considered to be parts of the global influenza epidemics.

The Hong Kong influenza virus epidemic in the USSR.

An epidemic wave of influenza associated with the A2/Hong Kong/68 virus reached the USSR in the second 10-day period of December 1968. During the first quarter of 1969 the epidemic involved almost all cities of the Soviet Union. The intensities of the rise and of the fall of the 1969 epidemic wave were less pronounced than those of the 1965 influenza A2 epidemic, but were more extended. In most towns the epidemic lasted 50-80 days whereas in 1965 the epidemic in towns lasted 25-30 days.The influenza caused by A2/Hong Kong/68 was characterized by an unusual age-group distribution. Children under 7 years of age made up only one-quarter of the total influenza cases during the peak of the epidemic wave in most communities. The clinical course of the disease was, in the main, of average severity, there being no significant differences in symptoms compared with influenza caused by virus A2.Analysing the influenza epidemics associated with influenza A2 virus during recent years one may note peculiar features of the A2 Hong Kong/68 influenza epidemic. On the one hand, these are apparently connected with the shifts in antigenic character of the virus, and, on the other hand, with the timely arrangements undertaken by public health services to prepare for the influenza epidemic, i.e., the carrying out of prophy actic and anti-epidemic measures.

Evaluation of the effectiveness of large-scale vaccination against influenza in the USSR.

Vaccination is at present the only means of influenza control; so far, large-scale trials of live vaccine have been made mainly in the USSR. This paper discusses such a trial in persons above 12 years of age.About 40% of the population of Smolensk and about 50% of the population of the nearby town of Jarcevo were vaccinated with live influenza vaccine in the winters of 1964-65 and 1965-66, and the incidence of influenza and other acute respiratory diseases in these towns during the 1965 epidemic and the 1966 pre-epidemic period was compared with that in nearby "control" towns. Most subjects were vaccinated 2 or 3 times with divalent A2-B vaccine in 1964, but some only once; in 1965-66, most subjects were vaccinated once with monovalent B vaccine and once with divalent A2-B vaccine.Analysis of the incidence data for the towns involved, of more detailed incidence data for about 30 000 workers and 4000 schoolchildren in Smolensk and one control town, and of a controlled trial involving about 4000 persons, indicated that the large-scale vaccination led to a reduction in incidence of about 1.5- to 2-fold in 1965 and of about 2- to 3-fold in 1966. Limited serological studies in 1966 indicated that the reduction in incidence in the group studied was not 3-fold but 4-fold. The rather low protection offered by the 1964 vaccination may have been due to the low immunogenicity of the vaccine, or to the fact that the vaccine strains used did not correspond exactly to the influenza virus strains circulating in nature.

The 1965 A2 influenza epidemic in the USSR and the natural history of Asian influenza.

An epidemic of Asian (A2) influenza that occurred in the USSR early in 1965 was the fourth wave of Asian influenza there since 1957, when the disease became pandemic, spreading through all countries and continents. The 1965 epidemic was severe, in several cities even more so than the 1957 pandemic. Study of the antigenic structure of the viruses isolated during the latest epidemic indicated that the viruses were similar to those isolated in western Europe in 1964 (A2/England 12/64) but that their structure showed a further shift away from that of the prototype virus (A2/Singapore 1/57). The 1957 and 1959 pandemics followed similar courses, starting in China. The third wave affected Europe. North Africa and Asia in winter 1960-61, but did not reach the USSR until the following winter. The fourth wave was more complex, spreading in Asia in 1962-63 and in Europe and America in 1963-64; it reached the USSR at the beginning of 1965. The way in which the structure of the A2 virus has changed since 1957 is discussed.