Epidemiology of twin births from a climatic point of view. The twinning rate was analysed using figures taken from statistics for Japan. During the years 1955 to 1959 there were 58 570 twin deliveries out of a total of 9 088 233, a frequency of 6-44 per 1000. Using Weinberg's differential method for zygosity estimation, the monozygotic twinning rate was 4 04 per 1000 and the dizygotic was 2-40. Twinning rates in 46 prefectures were also estimated and their correlations with meteorological parameters as well as with the mortality from cerebrovascular disease were examined. The twinning rates increased from a low level in the south west to a high level in the north east of Japan. The tendency was more obvious for the dizygotic than the monozygotic twinning rate. A negative correlation was observed between incidence rates of dizygotic twins and mean airtemperatures throughout the year, and a positive one between incidences of dizygotic twins and mortality rates for vascular lesions affecting the central nervous system in 46 prefectures. A seasonal variation of twinning rates was also observed in Niigata City for statistics of births during the periods 1948-55 and 1963-70. This took the form of a bimodal curve, with high conception rates for twin births in intermediate mild seasons, the spring and autumn and, low rates in the more stressful hot and cold seasons. These relationships between climate and twin births within a single race-group are discussed.

The reactogenicity and immunogenicity of Tween-ether split trivalent A(H1N1), A (H3N2), and B influenza vaccine in primary school children aged seven to 12 years, and the persistence of antibodies following two doses of vaccine were studied during 1980-1984. Adverse reactions were infrequent, and, even when reported, were chiefly local ones, mild in nature and of short duration. Most of the reactions were less frequent after the second dose than after the first dose. Most of the systemic reactions occurred during the intervaccination period with almost equal frequency, indicating that careful consideration is required to judge whether they were induced by vaccination or not. This vaccine had induced adequate hemagglutination inhibiting (HAI) antibody because the geometric mean titers (GMTs) of the vaccinees were two-to eightfold higher than those of the nonvaccinees to any of the vaccine antigens following two doses of vaccine. In general, the responses to A(H3N2) virus were the best among the vaccine antigens through the four vaccination seasons, but there was a tendency to show a poorer response to the same type (or subtype) of virus antigen as the causative one during a protracted epidemic. The antibodies induced by either vaccination or natural infection were shown to persist for less than a year, supporting the recommendation for annual vaccination.

A survey of the chromosome constitution in 500 induced abortions (5-12 menstrual weeks) was undertaken over a period of 1 1/2 years. There were 34 cases (6.8%) of gross chromosome anomalies: 2 cases of trisomy A; 5 of trisomy C (including XXX and XXY); 1 of mosaic trisomy C; 4 of trisomy D; 2 of trisomy E; 2 of trisomy G; 1 of double trisomy E and G; 1 of XYY; 4 of monosmy C (including XO); 2 of mosaic monosomy C; 1 of mosaicism of ring D chromosome; 1 of extra small metacentric chromosome; 3 of triploidy (including triploidy with double trisomy C and G); and 5 of tetraploidy and its mosaicism. An increased risk for the occurrence of trisomic anomalies was found with advancing age of the mothers. In contrast, the production of monosomies was not age-related. Trisomies were the most common type of anomalies and were found almost at random, regardless of the characteristics of chromosomes. Neither satellited nor small chromosomes were predominantly involved in the formation of chromosome anomalies.

Epidemiology of twin births from a climatic point of view. The twinning rate was analysed using figures taken from statistics for Japan. During the years 1955 to 1959 there were 58 570 twin deliveries out of a total of 9 088 233, a frequency of 6-44 per 1000. Using Weinberg's differential method for zygosity estimation, the monozygotic twinning rate was 4 04 per 1000 and the dizygotic was 2-40. Twinning rates in 46 prefectures were also estimated and their correlations with meteorological parameters as well as with the mortality from cerebrovascular disease were examined. The twinning rates increased from a low level in the south west to a high level in the north east of Japan. The tendency was more obvious for the dizygotic than the monozygotic twinning rate. A negative correlation was observed between incidence rates of dizygotic twins and mean airtemperatures throughout the year, and a positive one between incidences of dizygotic twins and mortality rates for vascular lesions affecting the central nervous system in 46 prefectures. A seasonal variation of twinning rates was also observed in Niigata City for statistics of births during the periods 1948-55 and 1963-70. This took the form of a bimodal curve, with high conception rates for twin births in intermediate mild seasons, the spring and autumn and, low rates in the more stressful hot and cold seasons. These relationships between climate and twin births within a single race-group are discussed.

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