[Epidemiological study of the prevalence of influenza in Japan--regional differences in terms of three indices (development of epidemic outbreak, viral isolation, peak of prevalence)].

The prevalence of influenza in Japan was studied, dividing the whole country into six sections such as Tohoku, Hokkaido and Kanto, to determine regional differences from the nationwide viewpoint. This study was based on data obtained from a total of 720 prefectures where three of the first index (the time the epidemic outbreak developed), second index (the time the virus was isolated) and third index (the time the prevalence reached its peak) were determined for the 16 prevalence periods of influenza between 1976 and 1993. The mean value (standard deviation) of each index was obtained for each year of prevalence and for each area. The differences obtained were analyzed statistically, and the following results were obtained: 1. There was a marked regional difference in the development of epidemic outbreak of cold; it was earliest in the Kanto and Kinki areas (late November to early December) and latest in the Kyushu area (mid January). 2. Isolation of the virus was earliest in the Kanto and Kinki area (mid January) and latest in the Chugoku and Shikoku areas (late January to early February), showing a regional difference. 3. The peak of prevalence was earliest in the Kanto area (early February) and latest in the Tohoku, Hokkaido, Chugoku and Shinkoku areas (mid February), showing a regional difference. 4. The difference between the earliest and latest areas was 4.2 weeks regarding the first index, while it was decreased to 1.8 weeks for the second index and to 0.8 weeks for the third index.(ABSTRACT TRUNCATED AT 250 WORDS)

[Characteristic features of children subjected to vaccination against influenza--in view of the state of their absence from school during a non-prevalence period].

Characteristic features of children subjected to vaccination against influenza were analyzed in view of the state of their absence from school during a non-prevalence period of this disease. A total of 31,902 children were divided broadly into those with a history of asthma, allergy or cardiac disease [disease history group, 1,048 (3.3%) children] and those without such a history [non-disease history group, 30,854 (96.7%) children]. Each group was further divided into three subgroups according to the number of inoculations (0, 1, 2 inoculations) given during the period between October and November 1988. The three subgroups in each group were compared statistically with regard to the state of absence from school during the non-prevalence period of influenza between April and July 1988, and the following results were obtained. 1. Disease history groups. There was no significant difference among the three subgroups with regard to the rate of absenteeism or mean number of days of absence. Also, no significant difference among them was found in the overall or segmental distribution of days of absence. These findings indicate that the three subgroups of children with a history of disease were almost homogeneous. However, the overall rate of absenteeism was significantly high among children who received one inoculation (p less than 0.001). In this subgroup, the number of children who were absent from school for 21-30 days was greater than that of children who were absent for fewer days. This contributed to the highest overall rate of absenteeism in this subgroup.(ABSTRACT TRUNCATED AT 250 WORDS)

[Epidemiological study on the effects of influenza virus vaccines--based on the state of absence examined in elementary school children as a whole and in children with a history of disease].

The effects of commercially available HA influenza vaccines, produced in 1988, was investigated in pupils in elementary schools located in six cities in Saitama Prefecture during the prevalence of influenza from 1988 to 1989. The state of absence in the children as a whole and in those with a history of disease was examined statistically, by dividing them into three groups in terms of the number of vaccinations given. The following results were obtained. 1) The proportion of children who had received no vaccination (71.2%) was significantly higher than that of children who had received one (9.6%) or two (19.3%) vaccinations. 2) A history of disease was found in 1,048 (3.3%) of the 31,941 children. The percentage of children having such a history was 3.6%, 2.7% and 2.5% among those who had received 0, 1 and 2 vaccinations, respectively; those who had no such history accounted for more than 96.0% in each group of children. 3) There were no differences between the three groups of children with regard to the proportion of those who had a history of respiratory or circulatory symptoms. 4) The rate of absenteeism and the overall rate of absenteeism were found to be significantly higher in children without any vaccination than those with two vaccinations, regardless of whether all subjects were considered or only those who had a history of disease were considered. 5) Both among all subjects and among those who had a history of disease, the mean number of days of absence was significantly high in children without any vaccination than those with 2 vaccinations.(ABSTRACT TRUNCATED AT 250 WORDS)

[Study on the effects of influenza virus vaccines--relation between the rate of two-fractional vaccination and the overall rate of absenteeism].

In 1987 and 1988, in 9 elementary schools, the percentage of children who received two sessions of vaccination and the overall rate of absenteeism resulting from influenza were determined for each class, and their relationship was investigated. The following results were obtained. 1) The mean vaccination rate was 58.6% among 157 classes in 1987, whereas it was 29.9% among 151 classes in 1988, the rate being significantly higher in 1987. 2) The mean overall rate of absenteeism was 1.524% in 1987, which was significantly lower than the corresponding rate, 2.802%, in 1988. 3) There was a significant negative correlation between the vaccination rate and the overall rate of absenteeism in 7 of the 9 schools in 1987; the overall rate of absenteeism became significantly low with an increase in the vaccination rate. 4) No such trend, however, was noted in any of the schools in 1988. 5) The difference between the results in 1987 and those in 1988 seems to be attributable to the facts that variability of the prevailing strains of influenza was low (V0, 82%) in 1987, in addition to the high vaccination rate in that year, and that influenza virus type B having a high variability (V3, or more, 78%) prevailed in 1988, when the vaccination rate was low.

Reinfection with influenza A (H2N2, H3N2, and H1N1) viruses in soldiers and students in Japan.

Reinfection with influenza A virus was studied by measuring hemagglutination-inhibiting antibody responses to infection in paired sera taken from groups of soldiers and students. Among 62 soldiers severely infected during the first wave of the A/Asian/57 (H2N2) pandemic in 1957, 17 were asymptomatically reinfected with the same virus within six months. In the 1962 epidemic the rate increased to 41%. Among reinfected soldiers studied, 68% had an asymptomatic infection; only 10% were severely symptomatic, and they were found to be infected with a virus closely related to A/Asian/57. For H3N2 epidemics, the rate of reinfection was 17% among students studied in 1970 who were reinfected with a virus closely related to the prototype A/Hong Kong/68 (H3N2). Reinfection with an extremely drifted variant of H3N2 was found to be 32% and 69% in two groups of students studied in 1972. Reinfection with a related virus was 32% in another group studied in 1983. Among the students studied who were reinfected with H3N2 viruses, the rates of asymptomatic infection were similar to those of symptomatic infection. The reinfection rates with a virus related to A/USSR/77 (H1N1) were 9.3% and 20% in two groups studied in 1980.