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Bacterial adherence to virus-infected respiratory tract cells may be one of the several mechanisms whereby virus predisposes to bacterial pneumonia. To evaluate the effect of influenza virus infection on pneumococcus adhesion, 39 mice were infected with PR8/A influenza virus. The adherence of radiolabeled pneumococcus to mice tracheal cells was determined 2, 4, and 6 days after viral inoculation. The pneumococcal adhesion to infected tracheas was significantly enhanced on Day 6 (p less than 0.001). Scanning and transmission electron microscopy revealed that by the fourth and sixth days after virus inoculation, the ciliated and the secretory cells of the tracheal epithelium had desquamated and the mucosa were coated with a continuous layer of basal cells. In a few cases, a desquamation of the basal layer was observed and the exposed basement membrane appeared as a pole of attraction for bacteria. Pneumococci were never seen attached to control tracheas. In contrast, they were observed adhered to the microvilli of the basal cells and, to a greater extent, to the exposed basement membrane.

The isolation of influenza virus 80 years ago in 1933 very quickly led to the development of the first generation of live-attenuated vaccines. The first inactivated influenza vaccine was monovalent (influenza A). In 1942, a bivalent vaccine was produced after the discovery of influenza B. It was later discovered that influenza viruses mutated leading to antigenic changes. Since 1973, the WHO has issued annual recommendations for the composition of the influenza vaccine based on results from surveillance systems that identify currently circulating strains. In 1978, the first trivalent vaccine included two influenza A strains and one influenza B strain. Currently, there are two influenza B lineages circulating; in the latest WHO recommendations, it is suggested that a second B strain could be added to give a quadrivalent vaccine. The history of influenza vaccine and the associated technology shows how the vaccine has evolved to match the evolution of influenza viruses.

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Oligonucleotide analysis of two avian influenza A viruses (Hav6N2 and Hav6Nav4) isolated in nature showed identical or almost identical patterns for the corresponding M and HA genes: 24 of 25 and 13 of 13 large oligonucleotides were indistinguishable by two-dimensional gel analysis. On the other hand, remarkable differences in the oligonucleotide patterns of the remaining genes were observed. Only 2 of 11 oligonucleotide spots of the NS gene, 10 of 27 spots of the NA/NP genes, and 22 of 49 spots of the P genes were indistinguishable between the two strains. On the basis of this observation that at least two genes of these viruses are virtually identical whereas others show easily detectable differences, we conclude that the two avian strains are related to each other by a recombinational event. In addition, it was found that animals in nature can be doubly infected with influenza viruses. Both lines of evidence strongly suggest that recombination is at least one mechanism by which "new" influenza virus strains emerge in nature.

The clinical reaction and the immunological response to influenza virus vaccine were studied in 43 B-cell chronic lymphocytic leukaemia patients. The Vaxigrip vaccine was administered containing the antigens A/Ghizhou/54/89, A/Singapore/6/86, and B/Yamagata/16/88. The side-effects observed were minimal and well tolerated. Antibody production with titres > 1:20 on day 15 was observed at least for one antigen in 35 patients (81%). In 23 of them (63%) this response was retained on days 30 and 60. Patients with IgG levels ( < 700 mg/dl) responded lesswell as compared to those having normal IgG levels ( > 700 mg/dl).

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