Immunization of elderly volunteers with the 1988-89 inactivated whole influenza vaccine: assessment of antibody responses by haemagglutination inhibition and single radial haemolysis tests

Early kinetics of antibody response to inactivated influenza vaccine

The aim was to examine the rapidity of haemagglutination inhibiting (HI) antibody response induced by immunization with a current inactivated trivalent influenza vaccine. Five to six sequential serum samples collected in autumn 1992 from each of 68 vaccinees in three age groups were studied for HI antibodies to ten influenza virus strains representing vaccine and epidemic viruses. Geometric mean titres, response rates and protection rates are presented. Response rates of > 70% were overall, but not until two weeks after the vaccination. Significant two- and four-day post-vaccination antibody responses were detected only occasionally. In previously vaccinated persons, average antibody titres to some of the viruses decreased during the first days after the vaccination. In the subsequent samples, the titres remained lower than in persons who were not vaccinated against influenza in preceding years. Protection against influenza infection may be frequently developed not until two weeks after vaccination. This has relevance to prophylactic administration of amantadine and rimantadine when an influenza A outbreak is imminent and the vaccination is late.

Safety and immunogenicity of a paediatric presentation of an influenza vaccine

BACKGROUND

Flu vaccination in otherwise healthy infants and young children is important to prevent severe disease, as well as to control epidemic spread of influenza infection.

AIMS

To examine the safety and immunogenicity of a paediatric presentation of a purified, inactivated, triton split influenza vaccine.

METHODS

Two doses of the vaccine, provided in prefilled syringes of 0.25 ml, were administered, one month apart, to 67 children under 3 years of age.

RESULTS

Nine cases of immediate reaction to vaccination (macules/papules) were observed after the second injection only. During the study period, 9% of children experienced at least one delayed local reaction, and 28% of children presented at least one systemic reaction. Almost all reactions were mild and transient. Immunogenicity results surpassed the European Community recommendations for a 0.50 ml dose of vaccine in adults.

CONCLUSION

This paediatric formulation of inactivated flu vaccine appears safe and immunogenic in children from 6 months to 3 years of age; the convenient presentation in a prefilled syringe of 0.25 ml volume will facilitate administration of the dose recommended for young children.

Possible correlation between low antigenic drift of A(H1N1) influenza viruses and induction of HI antibodies

This study examined whether, during a seven-year period of low A(H1N1) influenza virus antigenic drift (1988-1989 and 1994-1995, winters), humoral antibody response of elderly volunteers to influenza vaccines could suggest a lack of antibody pressure for drift. In all the years studied A/Taiwan/1/86, the A(H1N1) vaccine component, had a low ability to induce protective hemagglutination-inhibiting (HI) antibody titres (> or = 1:40). However a similar low immunogenicity was found for some of the different A(H3N2) strain variants of influenza virus, co-circulating in the same period and showing a regular extent of antigenic variations. Although our data could be at least in part explained by the type of study population (elderly and repeatedly vaccinated), postepidemic serological studies did not evidence a consistently lower ability in mounting protective immune response in elderly people as compared with younger against the influenza strains studied. Therefore, our present results did not exclude a true low immunogenicity of A/Taiwan and of some A(H3N2) influenza strains, circulating in the winters examined. This suggests that, besides the necessity to evade prior immunity, additional factors could influence the frequency of influenza viruses antigenic drifts.

HI antibody kinetics in adult volunteers immunized repeatedly with inactivated trivalent influenza vaccine in 1990-1992

Volunteers were immunized once, twice or three times in 1990-1992 with commercial trivalent inactivated influenza vaccine and monitored for haemagglutination inhibition (HI) antibodies. The antibodies that already existed when the subjects entered the study derived from natural infections. Immunizations in the second and third years were necessary to maintain the geometric mean titres of antibody and protection rates at the level recorded after the first vaccination. Negative correlations between prevaccination antibody titres and mean fold antibody increases were noted in most instances analysed. Moreover, at each individual prevaccination titre level the mean fold antibody increases and even postvaccination mean titres were higher after the first than after subsequent vaccinations, suggesting that the HI antibody responses might be affected by vaccine-induced pre-existing antibody more than by the same titres of antibody derived from natural infections. This was most obvious for antibody to the H1N1 subtype virus, A/Finland/164/91. In immunization with B/Yamagata/16/88, anamnestic response of antibody to B/Finland/150/90, which belongs to the antigenically distinct lineage of B/Victoria/2/87-like viruses, was more frequent in the first than in subsequent years. This is in contrast to homologous antibodies, which increased significantly after the second vaccination.