Comparison of US inactivated split-virus and Russian live attenuated, cold-adapted trivalent influenza vaccines in Russian schoolchildren.

In a blinded, placebo-controlled study, the reactogenicity, immunogenicity, and clinical efficacy of single doses of US inactivated split-virus and Russian live attenuated, cold-adapted influenza vaccines were compared in 555 schoolchildren in Vologda, Russia. Serial serum samples were collected and school absenteeism was assessed. Systemic reactions were rare, but local reactions (primarily erythema at the injection site) were observed in 27% of the inactivated vaccine group, and coryza (12%) and sore throat (8%) were observed in the attenuated vaccine group.

Class-specific antibody responses in school children vaccinated with an A/Brazil/11/78 (H1N1)-like recombinant influenza virus prepared from the A/Leningrad/134/57 paediatric cold-adapted donor strain.

Forty-three school children from 8 to 11 years old were vaccinated intranasally with two doses of a paediatric attenuated influenza vaccine developed by reassortment between cold-adapted A/Leningrad/134/57(H2N2) and an A/Brazil/11/78(H1N1)-like strain. Two vaccine doses were administered 1 month apart in a randomized, blind, placebo-controlled study. Although the first vaccine dose had a low infectivity titre, overall 65% of children who received two doses of vaccine showed serological evidence of infection by HI tests.

Interfering activity of epidemic, attenuated and recombinant strains of influenza A virus.

Interfering activity (IA) of the epidemic and attenuated influenza virus strains of different ts-phenotype was studied. IA was assessed by inhibition of vaccinia virus cytopathic effect in chick embryo chorioallantoic membrane (CAM) cells. Direct relationship was established between the temperature sensitivity (ts) index and IA of these viruses.

Study of live recombinant cold-adapted influenza bivalent vaccine of type A for use in children: an epidemiological control trial.

Live cold-adapted recombinant bivalent vaccine of influenza type A was studied in a controlled field trial in 1982-1983 among nearly 30,000 children 3-15 years old. The bivalent vaccine consisted of recombinants 47/25/1 (H1N1) and 47/7/2 (H3N2) of wild-type viruses A/Brazil/11/78 (H1N1) and A/Bangkok/1/79 (H3N2) with cold-adapted donor A/Leningrad/134/47/57 (H2N2). The recombinants which received mutant nonglycoprotein genes from cold-adapted donor did not suppress each other after simultaneous inoculation of children and stimulated antibody response to both strains.

Recombinant cold-adapted attenuated influenza A vaccines for use in children: reactogenicity and antigenic activity of cold-adapted recombinants and analysis of isolates from the vaccinees.

Reactogenicity and antigenic activity of recombinants obtained by crossing cold-adapted donor of attenuation A/Leningrad/134/47/57 with wild-type influenza virus strains A/Leningrad/322/79(H1N1) and A/Bangkok/1/79(H3N2) were studied. The recombinants were areactogenic when administered as an intranasal spray to children aged 3 to 15, including those who lacked or had only low titers of pre-existing anti-hemagglutinin and anti-neuraminidase antibody in their blood. After two administrations of vaccines at a 3-week interval, both strains induced antibody in 75 to 95% of the children.

Recombinant cold-adapted attenuated influenza A vaccines for use in children: molecular genetic analysis of the cold-adapted donor and recombinants.

A previously described cold-adapted attenuated virus, A/Leningrad/134/17/57 (H2N2), was further modified by 30 additional passages in chicken embryos at 25 degrees C. This virus had a distinct temperature-sensitive (ts) phenotype, grew well in chicken embryos at 25 degrees C, and failed to recombine with reference ts mutants of fowl plague virus containing ts lesions in five genes coding for non-glycosylated proteins (genes 1, 2, 5, 7, and 8). Recombination of A/Leningrad/134/47/57 with wild-type influenza virus strains A/Leningrad/322/79 (H1N1) and A/Bangkok/1/79(H3N2) yielded ts recombinants 47/25/1(H1N1) and 47/7/2 (H3N2).

Location of ts defects in the genome of cold-adapted recombinant influenza A virus vaccine strains.

The ts phenotype and location of ts mutations were studied in the genome of parent viruses and those obtained by recombination of cold-adapted strains A/Leningrad/134/17/57 or A/Leningrad/134/47/57 with epidemic H1N1 and H3N2 influenza A virus strains. The epidemic H1N1 and H3N2 strains under study possessed a ts phenotype and contained ts mutations in one or two genes. The ts phenotype was lost following three clonings at 40 degrees C, suggesting that influenza virus strains isolated from humans may be heterogeneous and contain virions either carrying or not carrying the ts mutations in their genomes.

[Cold-adapted strain of A/Leningrad/134/47/57 (H2N2)--a special attenuation donor of live influenza vaccine for children and the isolation of its recombinants].

A cold-adapted A/Leningrad/134/47/57 (H2N2) strain, a special donor of attenuation for generation of recombinant vaccine strains safe for children, has been developed and characterized. The genetic markers of this virus (temperature sensitivity of the cold-adapted strain, temperature optimum of the neuraminidase activity) were compared with those of A/Leningrad/134/17/57 (H2N2) strain, a donor of attenuation for a live influenza vaccine for adults. The A/Leningrad/134/47/57 (H2N2) strain was found to have a more marked temperature sensitivity and cold adaptation which correlated with the presence in its genome of multiple temperature-sensitive mutations in genes 1, 2, 5, 7, and 8.

Peculiarities of obtaining and characterization of a cold-adapted A/PR/8/34 influenza virus variant.

The dynamics of alterations in biological properties of A/PR/8/34 virus strain was studied in the process of prolonged adaptation to the growth in chick embryos (CE) at a lowered (25 degrees C) cultivation temperature. The variant selected after 59 passages and subsequent cloning at the above temperature retained the high reproductive capacity in CE at optimal temperature (34 degrees C) - a characteristic of the original strain. Unlike to the latter, it showed a distinctly reduced ability to reproduce at 40 degrees C and a lower level of pathogenicity for white mice and CE.

[Safety and high immunogenicity for children 3 to 15 of a mono- and a divaccine from recombinant influenza A/Brazil /11/78 (H1N1) and A/Bangkok/1/79 (H3N2) viruses obtained from a special donor attenuation base--the cold-adapted virus A/Leningrad/134/47/57 (H2N2)].

The data on complete safety and high immunogenic potency of intranasal live influenza vaccine from the recombinant A/Brazil/11/78 (H1N1) and A/Bangkok/1/79 (H3N2) strains prepared with a special donor of attenuation, a cold-adapted A/Leningrad/134/47/57 (H2N2) virus, have been obtained. The possibility of using a bivaccine from the recombinant strains constructed on the basis of a single donor of attenuation and inheriting from it most of the genes coding for nonglycosylated proteins was demonstrated. Administration of this bivaccine to children was not accompanied by any increase in the rate of postvaccination febrile reactions, but produced in the vaccinees an intensive immune response to the antigenic components of the vaccine which was in agreement with the data obtained after separate administration of monovaccines.

Attenuated ts-recombinants of influenza A/USSR/77 (H1N1) virus obtained by crossing with the cold-adapted donor A/Leningrad/134/57 (H2N2) virus.

Conditions of obtaining attenuated influenza virus recombinants by crossing of a cold-adapted donor with A (H1N1) influenza virus that reappeared in 1977 were studied. Temperature-sensitive recombinants suitable for intranasal immunization of adults with low titres of anti-haemagglutinin and anti-neuraminidase antibodies, and possessing sufficiently high immunogenicity were obtained by crossing of native parent strains and cross-reactivation techniques. It was confirmed that the cold-adapted A/Leningrad/134/17/57 (H2N2) influenza virus variant is a prospective donor of attenuation for obtaining recombinants--candidates for live influenza vaccine strains.

Analysis of genome composition and reactogenicity of recombinants of cold-adapted and virulent virus strains.

Temperature-sensitive (ts) mutations occurring in three genes, 1, 2, and 7, and 1, 5 and 7 were found in two cold-adapted (ts) attenuated influenza virus strains A/Leningrad/9/37/46 (H0N1) and A/Leningrad/134/17/57 (H2N2) respectively. The recombinants, obtained by crossing these cold-adapted strains with virulent influenza virus strains, had different genome structures and inherited from one to six genes from the cold-adapted parents. Tests of reactogenicity of recombinants in volunteers showed all the recombinants to be non-reactogenic irrespective of the number of genes inherited from the cold-adapted parent.

Peculiarities of obtaining attenuated thermosensitive recombinants of influenza A virus at the end of the H3N2 epidemic cycle.

The conditions of obtaining thermosensitive recombinants of the virulent A/Leningrad/82/76 (H3N2) virus with two donors of attenuation, A/Leningrad/134/17/57 (H2N2) and A/Leningrad/9/37/46 (H0N1), were evaluated. The recombinants were obtained by various methodical approaches (hybridization of native viruses, cross-reaction and selection of recombinants at temperatures of 25, 32 and 40 degrees C) to study their effects on the degree of attenuation and the regularity of transmission of the ts marker. The recombinants examined varied in thermosensitivity which depended on the conditions of recombination of parent viruses.

Conditions for production of thermosensitive attenuated influenza virus recombinants.

Recombination and cross-reactivation between virulent influenza viruses and a cold-adapted thermosensitive vaccine strain regularly produced genetically stable attenuated recombinants, the selection of which was based on the thermosensitivity marker. This marker, correlating with the safety of the recombinants for man was inherited independently on the properties of the haemagglutinin and neuraminidase surface antigens. There was no relationship between the thermosensitivity of the resulting recombinants and the decrease in the optimal temperature of the neuraminidase activity (OTNA marker).