We established a reverse genetics system for the nonstructural (NS) gene segment of influenza A virus. This system is based on the use of the temperature-sensitive (ts) reassortant virus 25A-1. The 25A-1 virus contains the NS gene from influenza A/Leningrad/134/57 virus and the remaining gene segments from A/Puerto Rico (PR)/8/34 virus. This particular gene constellation was found to be responsible for the ts phenotype. For reverse genetics of the NS gene, a plasmid-derived NS gene from influenza A/PR/8/34 virus was ribonucleoprotein transfected into cells that were previously infected with the 25A-1 virus. Two subsequent passages of the transfection supernatant at 40°C selected viruses containing the transfected NS gene derived from A/PR/8/34 virus. The high efficiency of the selection process permitted the rescue of transfectant viruses with large deletions of the C-terminal part of the NS1 protein. Viable transfectant viruses containing the N-terminal 124, 80, or 38 amino acids of the NS1 protein were obtained. Whereas all deletion mutants grew to high titers in Vero cells, growth on Madin-Darby canine kidney (MDCK) cells and replication in mice decreased with increasing length of the deletions. In Vero cells expression levels of viral proteins of the deletion mutantswere similar to those of the wild type. In contrast, in MDCK cells the level of the M1 protein was significantly reduced for the deletion mutants.
Children aged 7-14 years in Novgorod, Russia, were given Russian live cold-adapted or inactivated influenza vaccines or placebo over a 2-year period. Schools were randomly assigned as a whole to one of the preparations. In the first year, the vaccines were bivalent, containing types A (H3N2) and A (H1N1) components. In the second year, the vaccines also contained a type B component. In the first year, all viruses isolated were type A (H3N2); in the second, about three-quarters of the isolates were type B and the rest type A (H1N1). During both years, the vaccines protected the vaccinated children. Where significant differences existed, the live attenuated vaccine was more protective than the inactivated. Vaccination rates in schools in which live attenuated vaccines had been used were inversely related to illness rates of staff and unvaccinated children, suggesting that viral transmission had been reduced by the vaccine.
A randomized population-based study has been carried out since 1985 in Leningrad in order to evaluate the efficacy of breast self-examination (BSE) in early breast cancer detection. The population under study covers 120,310 women aged 40-64 years with no history of breast cancer. About half of these women were exposed to BSE training (60,221) and 60,098 women constituted the control group. BSE teaching was carried out on a person-to-person basis and each patient received the BSE calendar. BSE education sessions resulted in a higher frequency of visits to specialists with complaints about "pathology" of the breast, a higher rate of referral to a specialized institution for an examination, and a higher number of excision biopsies due to a benign lesion (RR = 1.5; 95% C.I. = 1.1 - 1.9) as compared with the control group. As a result of examination, 190 breast cancer patients in the BSE group and 192 patients in the control group were detected. Comparisons of patients from both groups with regard to the size of primary tumor and the incidence of metastatic lesion in the regional lymph nodes showed no differences. The study is ongoing and all cases of breast cancer in the BSE group will be registered up to 1994 and followed-up to 1999; information will then be available on the impact of BSE upon breast cancer mortality.
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