[Neuraminidase inhibitors oseltamivir and zanamivir: new means of defence against influenza]

Recently two new neuraminidase inhibitors zanamivir and oseltamivir have been marketed. They appear to considerably reduce morbidity and mortality from influenza. Their adverse effects are infrequent and mild and the chance of development of pathogenically significant resistant mutants appears to be small. During the first six months of a pandemic, neuraminidase inhibitors are the only defence against the virus. It is therefore important to stockpile in each country sufficient quantities of these drugs. During the usual influenza epidemics the main value of neuraminidase inhibitors lies in their use for therapy, prophylaxis and post-exposure prophylaxis in long-term care institutions for the elderly (for prophylaxis only oseltamivir is licensed). Although data on the effectiveness against complications of influenza and on the effect on people with an increased risk of (fatal) complications as a result of an influenza virus infection are limited, the available information on the effects of the neuraminidinase inhibitors indicates that these drugs will also protect against complications and that high-risk groups will benefit from the rapid deployment of these products. The cost-effectiveness of treatment and post-exposure prophylaxis with neuraminidinase inhibitors is probably not favourable for healthy children and adults but seems to be favourable for the high-risk groups (vaccinated or not) in winter.

A randomized, double blind study in young healthy adults comparing cell mediated and humoral immune responses induced by influenza ISCOM vaccines and conventional vaccines

Although current influenza vaccines have been shown to reduce influenza-related morbidity and mortality, there is a desire to develop more efficacious products. Vaccines which can induce CD8(+) cytotoxic T cell (CTL) responses in addition to strong antibody responses may be more effective in preventing disease since it has been demonstrated that CTL contribute to protective immunity, even against drift variants of influenza A viruses. The immunogenicity of two types of experimental influenza vaccines, which were based on immune stimulating complexes (ISCOM), were evaluated and compared with a conventional non-adjuvanted inactivated split virion vaccine, after immunization of human volunteers. In this randomized, double blind study, it was shown that the ISCOM vaccines altered the kinetics of the serum antibody response, resulting in more rapid titer rises against the vaccine strains. This accelerated antibody response coincided with enhanced in vitro proliferative T cell responses, which were observed shortly after vaccination. In addition, CTL responses were observed in a higher proportion of the vaccinees receiving an ISCOM vaccine, than in vaccinees receiving the conventional influenza vaccine.

Mismatch between the 1997/1998 influenza vaccine and the major epidemic A(H3N2) virus strain as the cause of an inadequate vaccine-induced antibody response to this strain in the elderly

The success of influenza vaccination depends largely on the antigenic match between the influenza vaccine strains and the virus strains actually circulating during the season. In the past, this match has proved to be satisfactory in most seasons. In the 1997/1998 season, however, hemagglutination inhibition (HI) assays with ferret antisera indicated a considerable mismatch between the H3N2 vaccine component and the most prevalent epidemic influenza A(H3N2) virus. The results from antigenic analyses using pre- and postvaccination serum samples from volunteers of various ages, including residents of nursing homes who were more than 60 years of age, were in good agreement with the results obtained with ferret antisera. Homologous serum antibody responses to the H3N2 vaccine component as well as the cross-reactivity of the induced antibodies to the epidemic H3N2 strain, declined with increasing age of the vaccinees. As a consequence of these two effects, 84% of the vaccinees over 75 years of age did not develop HI antibody titers >/= 40 against the major H3N2 virus variant of 1997/1998, suggesting that they were not protected against infection with this virus variant. These findings support the current policy of the World Health Organization (WHO), which is to base worldwide influenza virus surveillance on results predominantly obtained by antigenic analyses of influenza virus isolates with ferret antisera in HI tests. If an antigenic mismatch is observed, the protective efficacy of the vaccine, especially for the elderly, may be insufficient. The observations also support the current policy to include the elderly in serologic efficacy trials.

Efficacy of influenza vaccination in adult liver transplant recipients

To assess the efficacy of influenza vaccination in immunocompromised adult liver transplant (LTx) recipients, the serum antibody responses of 61 of these patients and 35 liver cirrhosis patients with those of 45 of their healthy spouses were compared, after one and two vaccinations with a commercial trivalent subunit influenza vaccine. In addition, virus-specific proliferative T-cell responses were measured in LTx recipients and their healthy spouses. In all three study groups, significant rises in geometric mean antibody titers were observed for all three antigens after one vaccination. These titers did not continue to increase significantly after the second vaccination in patients with cirrhosis and control subjects but did rise for LTx recipients. The overall antibody response to all three influenza virus strains proved to be significantly lower in the LTx recipients than in the group of healthy subjects after both one and two vaccinations. More than 68% of the LTx recipients developed hemagglutination-inhibiting serum antibody titers >/=40 against all three vaccine strains after the first vaccination and more than 80% after the second vaccination. These findings correlated with the T-cell responses determined for the group of LTx recipients and healthy control individuals. Testing of the respective serum samples against influenza virus A/Sydney/5/97, which circulated in the 1997-1998 influenza season and showed a considerable mismatch with the vaccine strain A/Nanchang/933/95, indicated that such a mismatch may have significant consequences for vaccine efficacy, especially for LTx recipients. Collectively the data show that LTx recipients can be vaccinated effectively against influenza despite immunosuppressive therapy. A two-dose vaccination regimen improved vaccination efficacy in LTx recipients. Whether transplant patients generally benefit from a two-dose vaccination regimen should be evaluated further.

Protection against influenza after annually repeated vaccination: a meta-analysis of serologic and field studies

BACKGROUND

According to common recommendations, influenza vaccination should be performed annually. It has been suggested that vaccination in previous years reduces vaccine efficacy in the long term.

OBJECTIVE

To determine whether the protection of influenza vaccine decreases when vaccination is repeated annually.

METHODS

Articles published between 1966 and 1997 were selected from MEDLINE. The end point for field studies was the influenza-related morbidity or mortality during influenza outbreaks (resulting in field protection rates). The end point for serologic studies was exceeding a protective postvaccination hemagglutination-inhibition titer (serologic protection rates). Protection rate differences between groups with single and multiple vaccinations were subjected to meta-analysis.

RESULTS

Seven field studies (including 13 trials) supported the hypothesis that protection in multiple-vaccination groups is at least as good as that in single-vaccination groups. Ten trials with 5117 observations could be subjected to meta-analysis. The pooled protection-rate difference was close to 0 (1.1%; 95% confidence interval, -0.2% to 2.4%), thus detecting no difference between single or multiple vaccination. Twelve serologic studies (including 53 trials) showed heterogeneous results: 9 trials were significantly in favor of single vaccination, and 7 were in favor of multiple vaccination, but in most cases, there was no significant difference between the 2 vaccination groups. The pooled serologic protection-rate difference from 52 trials (12341 observations) was again close to 0 (1.7%; 95% confidence interval, -1.3% to 4.8%).

CONCLUSIONS

We did not detect any evidence for a decreasing protection with annually repeated influenza vaccination. Annual vaccination should not be discouraged in populations at risk.

The plea against annual influenza vaccination? 'The Hoskins' Paradox' revisited

Three papers by Hoskins and collaborators published in The Lancet in the 70s, have been challenging the common policy to annually vaccinate people at risk with inactivated influenza virus vaccine. From an analysis of a vaccination campaign in adolescent pupils of a boarding school and four influenza outbreaks in the period 1970-76, Hoskins et al. concluded that annually repeated vaccinations would not confer protection against epidemic influenza in the long-term ('Hoskins' Paradox'). A review of the papers revealed, however, that most of the study subjects were not consequently vaccinated every year and that most of the presented data were, therefore, not relevant for the problem of annually repeated influenza vaccination. When applying strict definitions of single vaccination (immunised immediately prior to the epidemic, but not in the years before) and multiple vaccination (immunised immediately prior to the epidemic, and also in the year(s) before), only two of four epidemics (A/England/42/72 (H3N2) in 1972/73 and A/Port Chalmers/1/73 (H3N2) in 1973/74) could be evaluated: in one case, no negative effect of repeated vaccination could be detected, in the second case, the attack rate difference between groups with single and multiple vaccination was of borderline significance. Data on two other epidemics (B/Hong Kong/8/73 in 1973/74 and A/Victoria/3/75 (H3N2) in 1975/76) could not be interpreted because of incomplete vaccination strategies. In conclusion, Hoskins' Paradox cannot be substantiated by Hoskins' own data. Considering other published data on the subject, it is suggested that no negative effect of annually repeated vaccination on protection against epidemic influenza exists.

Annually repeated influenza vaccination improves humoral responses to several influenza virus strains in healthy elderly

The benefit of annually repeated influenza vaccination on antibody formation is still under debate. In this study the effect of annually repeated influenza vaccination on haemagglutination inhibiting (HI) antibody formation in the elderly is investigated. Between 1990 and 1993 healthy young and elderly, both selected by the SENIEUR protocol, were vaccinated consecutively with commercially available influenza vaccines. The elderly had a lower HI antibody response after one vaccination as compared to the young against the A/Taiwan/1/86 (HINI), B/Yamagata/16/88 and B/Panama/45/90 strains. Annually repeated vaccination did not result in a decrease of the HI antibody titres against the A and B vaccine strains in both age groups. Moreover, the elderly had a significantly higher HI titre against the B strains after the second vaccination as compared to the first, resulting in comparable HI titres for young and elderly. Thus, annually repeated vaccination has a beneficial effect on the antibody titre against influenza virus and can contribute to a better antibody-response in the elderly.

Effects of repeated annual influenza vaccination on vaccine sero-response in young and elderly adults

Three cohort studies in adults were performed during the period from 1986 to 1989. Eight hundred and eighty-four subjects were, one or more times, immunized with influenza vaccines, and pre- and post-vaccination antibody titres were determined by hemagglutination inhibition tests. One thousand and one hundred and nineteen vaccination events in 681 subjects could be analysed by a comparison, per trial and per influenza (sub)type, between groups with and without influenza vaccination in previous years. Effect size, odds ratio and protection rate difference, were used as effect measures. Subjects with previous vaccination showed higher pre-vaccination antibody than those without. The average change of the post-vaccination proportion of subjects with high antibody titre value to previous vaccination, was +9.4% (95% CI: +5.3 to 13.6%) for A-H3N2 vaccine components, -2.1% (-8.1 to 3.9%, not significant) for A-H1N1 and -10.6% (-16.5% to -4.8%) for B. In a linear regression model, pre-vaccination titres and the status of previous vaccination were identified as factors significantly influencing post-vaccination titres. These findings are discussed in the context of a short review of the literature. It is concluded that the status of previous vaccination should always be addressed as an independent factor in serological vaccination studies.

Adjuvancy and reactogenicity of N-acetylglucosaminyl-N-acetylmuramyl-dipeptide (GMDP) orally administered just prior to trivalent influenza subunit vaccine. A double-blind placebo-controlled study in nursing home residents

One hundred and fifty-three nursing home residents received 0, 5, 25 or 50 mg N-acetylglucosaminyl-N-acetylmuramyl-dipeptide (GMDP) orally, and trivalent influenza subunit vaccine intramuscularly. One day after intervention, there was a strong increase of total leucocytes, monocytes and neutrophils in the groups receiving 25 or 50 mg GMDP. A GMDP dose dependent increase in systemic, but not in local, vaccine side-effects was observed. No significant differences in post-vaccination haemagglutination inhibiting serum antibody titres were observed between the four groups, indicating that oral administration of GMDP together with influenza vaccination, does not lead to a higher vaccine efficacy.

Gender differences in local and systemic reactions to inactivated influenza vaccine, established by a meta-analysis of fourteen independent studies

In order to determine whether there is a difference between genders in reported adverse reactions to inactivated influenza vaccine, a computerized database of serological studies was investigated. A standardized questionnaire was used to evaluate vaccine reactogenicity. A total of 1,800 vaccinees in 14 studies were analyzed separately for two age groups ( < 60 and > or = 60 years of age). Females reported significantly more local reactions than males. The pooled odds ratio for the outcome measure "any local reaction" was 0.32 (95% confidence interval, 0.26-0.40, significant) and 0.54 (95% Cl, 0.41-0.70, significant) for young and elderly adults, respectively. Similar results were obtained for the outcome measure "any systemic reaction." Previous exposure to influenza or influenza vaccine had no influence on reactogenicity. There were no gender differences in sero-responses. In conclusion, gender should be regarded as a predictor of reported reactions to influenza vaccine in both young and elderly adults and should be addressed in future study designs.

[Influenza epidemic in a nursing home caused by a virus not included in the vaccine]

In the autumn of 1992 two-thirds of the population of a nursing home in Amsterdam was vaccinated against influenza. However, in March 1993 an outbreak of an influenza like illness occurred with a morbidity rate of 49% and a mortality rate of 10%. There was sufficient serological evidence to show that the vaccine as such had induced adequate immunity. As the causative agent an influenza A/H3N2 virus was identified. The failing activity of the vaccine in this instance was apparently caused by the absence of sufficient antigen similarity between the A/H3N2 vaccine component and the epidemic virus ('vaccine mismatch').

Impact of influenza on mortality in relation to age and underlying disease, 1967-1989

Based on data from the Dutch Central Bureau of Statistics, the impact of influenza on mortality in The Netherlands was estimated for a 22.5-year period (1967-1989) in four age groups and three entities of disease, using Poisson regression techniques. Our analysis suggests that, on average, more than 2000 people died from influenza in The Netherlands each year, but in only a fraction of these deaths was influenza recognized as the cause of death. For each case of death registered as caused by influenza (registered influenza mortality), 2.6 additional cases of death registered as due to causes other than influenza, nevertheless, were influenza-related (non-registered influenza mortality). Therefore, the overall impact of influenza on mortality is estimated to be greater than registered influenza mortality by a factor of 3.6. Those under 60 years of age accounted for 5% of all non-registered influenza deaths, whereas people aged 60-69, 70-79 years and > 80 years accounted for 12%, 29% and 54% of such deaths, respectively. When extrapolating the figures for the Dutch population of 1989, we could attribute, on average per season-year, 82 deaths per 100,000 people > 60 years, 143 in people > 70 years, and 280 in people > 80 years. Of all non-registered influenza cases of death, 47% were estimated to occur in people with heart disease as a primarily reported cause of death, 23% in those with lung disease, and 30% in those with other diseases. This study stresses the serious effects of influenza, mainly in the elderly (95% of non-registered influenza mortality).(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody response after influenza immunization with various vaccine doses: a double-blind, placebo-controlled, multi-centre, dose-response study in elderly nursing-home residents and young volunteers

The dose effect (0, 10, 20 and 60 micrograms) of influenza subunit vaccine on the antibody response was investigated in nursing-home residents and young controls. The vaccine antigens were: A/Taiwan/1/86 (H1N1), A/Sichuan/2/87 (H3N2) and B/Beijing/1/87. For the influenza B antigen, the post-GMT and the 'percentage protective titre' increased significantly both in the young controls and nursing-home residents. No dose effect was observed for the A/Taiwan, and a minor dose effect for A/Sichuan. All vaccine doses were well tolerated by both groups. We conclude from our data that higher vaccine doses may result in a better antibody response against some antigens but not against others. Therefore, in general, increasing the vaccine dose is no adequate method to improve the antibody response.

Influenza vaccines: the effect of vaccine dose on antibody response in primed populations during the ongoing interpandemic period. A review of the literature

Health authorities tend to favour an increase of the antigen dose in inactivated influenza vaccines from < or = 10 micrograms haemagglutinin (HA) per vaccine strain to 15 micrograms HA/strain. The increased dose is expected to yield a meaningful increase in the number of subjects to be protected after vaccination. To verify this expectation, we have reviewed 20 published reports (1978-1991) of serological studies in which anti-HA-IgG antibody after different doses was measured. In the review, stratification groups of previously primed subjects were formed and the antibody response was estimated for doses of 10 and 15 micrograms HA by linear k*2-chi 2 model. Despite a considerable heterogenicity of study populations, study designs, vaccine types and strains, and antibody assays, the results were consistent in revealing high protection rates (> or = 75%) for a 10 micrograms HA dose of influenza A vaccine components. For both response and protection rates, an increase of the antigenic load from 10 to 15 micrograms HA was not associated with a meaningful increase of seroresponse: in 38 out of 39 stratification groups, the increase of response and/or protection rate varied between -9% and +8%, with a median of 1.5%. These results do not justify the expectation that a vaccine dose of 15 micrograms HA per strain would be clinically superior to a dose of 10 micrograms HA. Only in a group of immune-compromised patients on chronic intermittent haemodialysis were results in favour of a higher dose found, which may justify further evaluation in this special population.

Influenza: relation of mortality to morbidity parameters--Netherlands, 1970-1989

The purpose of this study is to investigate the relationship between the number of influenza-like illness (ILI), weekly registered by the general practitioners (sentinel stations), and the monthly overall influenza mortality in people over 60 years of age, provided by the Dutch Statistical Bureau during the period July 1970 to June 1989. The quantitative impact of influenza-morbidity is expressed by three summary parameters, calculated from the 52 (53) weekly ILI-figures per season-year, (i) their sum (i.e. global extent of an epidemic), (ii) their standard deviation, and (iii) their maximum (i.e. peak number of ILI during an epidemic). In the analysis influenza A subtype is also included. These four parameters are mutually compared with respect to their predictability for yearly total influenza mortality in the 19 season-years available. In most cases, the standard deviation and the peak number of ILI are more powerful for prediction of mortality, than the global extent of the epidemic. The peak number of ILI is of special interest. It is particularly useful for estimating the effect on current influenza mortality during an ongoing epidemic. From the model it is possible to calculate a threshold (of weekly ILI) beyond which mortality increases proportionately more than the number of illness episodes. By using the peak value of morbidity it is possible to calculate the minimal impact of epidemic mortality. This study indicates that the weekly number of influenza-like illnesses has a certain prognostic value for the real impact of influenza. An electronic surveillance system could detect immediately the threshold above which influenza mortality increases more than proportionally.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of immunomodulator thymopentin on impaired seroresponse to influenza vaccine in patients on haemodialysis

In a double-blind placebo-controlled multicentre study, the effect of the immunomodulator thymopentin (TP5) on the antibody production to trivalent influenza vaccine was tested in 108 patients on chronic intermittent haemodialysis (HD). Antibody production was determined in pre- and postvaccination sera. Compared to a group of 35 young healthy adult control subjects, HD patients showed a clearly impaired seroresponsiveness to all three vaccine components, regardless of treatment with TP5 or placebo. We conclude that TP5 administration is not able to enhance humoral immunity in patients on chronic intermittent HD.

Antibody induction by influenza vaccines in the elderly: a review of the literature

Conflicting results have been reported concerning the association between high age and response to influenza vaccines. Some authors have found a reduced response in aged subjects, others have found no difference or even better results as compared with younger control subjects. Seventeen papers were selected from international literature published in the period 1968-1988 for a review of the anti-haemagglutinin-IgG sero-response following vaccination: among 30 cases in which vaccine components could be studied independently, ten revealed a better immune response in young subjects than in the elderly, four found more favourable results in the elderly, and 16 could not detect any significant between-group-differences, the latter most probably because of a high type-2-error. Nine of these 16 cases tended to favour young subjects. These results were relativated by the finding that each paper had at least one of three methodological limitations: (1) the failure to exclude subjects with illnesses or using drugs influencing the immune system, (2) the failure to exclude subjects with previous vaccinations against influenza, (3) the failure to exclude subjects with high prevaccination antibody titres. The direction of these biases is such that failure to address any one issue will lead to an underestimate of the response of aged subjects. In view of the failure to control these biases, it was not surprising that the papers reviewed presented a heterogeneous picture. Thus, the association between high age per se and response to influenza vaccines, if any, has not yet been established. Suggestions are made for future studies in which admission criteria should control health state and previous exposure to influenza antigens.

Humoral immune response to influenza vaccination in patients with primary immunoglobulin A nephropathy. An analysis of isotype distribution and size of the influenza-specific antibodies

Primary IgA nephropathy (IgAN) is characterized by mesangial deposits of IgA1, increased serum IgA1 levels, and circulating immune complexes containing predominantly IgA1. It has previously been found that patients with IgAN have a higher than normal IgA response to vaccination, but the IgA subclasses have not been studied. To investigate whether the IgA hyperresponsiveness is limited to the subclass IgA1, which is involved in the pathogenesis of IgAN, we compared the immune responses of 18 patients with 22 healthy controls after intramuscular vaccination with inactivated influenza virus. Antibody titers were significantly higher (P less than 0.0001) for the IgA1 subclass in patients versus controls, but not for the other isotypes. A substantial portion of the IgA and IgA1 antiinfluenza immune response comprised polymers in both patients and controls. There was no preferential response of polymers in patients. Patients produced significantly more monomeric IgA1 antibodies than controls. These results show that patients with IgAN have a hyperresponsiveness limited to the subclass IgA1 and mainly expressed by an excess of monomers.

Intact humoral immune response in patients on continuous ambulatory peritoneal dialysis

After influenza vaccination no statistically significant difference in antibody response was observed between patients on continuous ambulatory peritoneal dialysis (CAPD) and healthy volunteers while a large group of hemodialysis (HD) patients was found to have a significantly lower response rate. This difference remained statistically significant when CAPD patients were compared to a matched HD group. As the antibody formation after influenza vaccination is a T cell-dependent phenomenon, the normal immune response to vaccination suggests an intact humoral and cellular immunity in CAPD patients.

Humoral immune response and delayed type hypersensitivity to influenza vaccine in patients with diabetes mellitus

The antibody response and delayed type hypersensitivity reaction to commercially available trivalent influenza vaccine in 159 patients with diabetes mellitus was compared with response and reaction in 28 healthy volunteers. A correction for prevaccination titres was made. No differences were found between diabetic patients and control subjects with respect to antibody response to the three vaccine strains as measured by the difference between geometric mean titres of post- and prevaccination sera. In Type 1 (insulin-dependent) diabetic patients the incidence of non-responders to two vaccine components was significantly increased (p less than 0.05). The delayed type hypersensitivity reaction to influenza antigen was significantly decreased in patients with high concentrations of glycosylated haemoglobin (p less than 0.01). These findings suggest a role for impaired immune response in the increased influenza morbidity and mortality in patients with diabetes mellitus. Implications for therapy and vaccination strategy are discussed.

Trivalent influenza vaccine in patients on haemodialysis: impaired seroresponse with differences for A-H3N2 and A-H1N1 vaccine components

One hundred and one patients on haemodialysis, 21 patients on peritoneal dialysis and 30 healthy controls received a trivalent split vaccine containing 15 micrograms haemagglutinin of a recent influenza A-H3N2, influenza A-H1N1 and influenza B strain, respectively. Antibody production after four weeks was determined by the haemagglutination-inhibition test and expressed as response rate, protection rate and overall mean fold increase. The patients on haemodialysis revealed a diminished seroresponse, as compared to patients on peritoneal dialysis and controls. For influenza A-H3N2, this was less distinct than for the other two antigens. In patients on haemodialysis the protection rate was 66% against the A-H3N2 vaccine component (versus 85% in controls, not significant), but only 25% against A-H1N1 and 27% against B (versus 84 and 77% in controls, p less than 0.001). Duration of haemodialysis up to eight years did not affect seroresponse. Patients on haemodialysis who were primed for influenza A-H1N1 in the period 1947-1957, reacted markedly better to the A-H1N1 vaccine component than subjects of other priming periods. A booster injection of the same vaccine dosage four weeks after the first immunization, performed in 98 patients on haemodialysis, was of little value: it had virtually no effect with regard to influenza A-H1N1 and influenza B, and showed, though significantly better, still poor results for A-H3N2. The differences in seroresponse between the A-H3N2 and A-H1N1 vaccine component suggest a major defect of primary, and a minor defect of secondary humoral response in patients on haemodialysis. The consequences for vaccine policy in these patients are discussed.

Impairment of the immune response to influenza vaccination in renal transplant recipients by cyclosporine, but not azathioprine

Influenza vaccination has been strongly recommended for immunosuppressed renal transplant recipients. However, immunosuppression may lead to impaired antibody responses. We studied the antibody response to an inactivated trivalent influenza vaccine in 59 renal transplant recipients with life-sustaining kidney function: 21 were on cyclosporine and prednisone, 38 on azathioprine and prednisone. Healthy volunteers (n = 29) and patients on hemodialysis (n = 28) served as controls. Despite comparable renal allograft function, cyclosporine-treated patients had a significantly lower immune response against influenza A viruses than azathioprine-treated patients, whether mean antibody levels, fourfold titer rise, or seroconversion to protective titers was analyzed. No significant differences in antibody responses were found between healthy controls and patients on azathioprine. The patients on hemodialysis showed an impaired response to vaccination. However, in contrast to the cyclosporine-treated patients, booster immunization proved valuable in this group.

Immunoglobulin G, A and M response to influenza vaccination in different age groups: effects of priming and boosting

Fifty volunteers, treated with an inactivated trivalent influenza vaccine containing A/Bangkok/1/79 (H3N2), A/Brazil/11/78 (H1N1) and B/Singapore/222/79 virus, were subdivided according to the estimated first exposure to influenza in their lifetime (priming) and the presence of antibodies against the vaccine components in the pre-vaccination sera. The isotypic antibody response (IgG, IgA, IgM) was determined by means of an antibody capture haemadsorption immunosorbent technique. For all three vaccine components, previously seropositive subjects produced antibodies of the IgG- and IgA-class more frequently than previously seronegative persons. Subjects primed to one of the influenza A subtypes showed more IgG and IgA responses in comparison with those unprimed (prime-effect). In contrast, IgM antibodies occurred in only 19 and 11% of primed, but in 59 and 54% of unprimed subjects, for A (H3N2) and A (H1N1), respectively. The incidence of IgM titre rises was not influenced by the prevaccination state. However, the mean magnitude of anti-A (H1N1)-IgM titre rises was greater in those previously seronegative. The concepts of primary and reinfection and of 'original antigenic sin' are discussed, and it is suggested that age and, if possible, serological state prior to antigen-exposure should be taken into account when studying isotypic antibody responses after influenza infection or vaccination.

Influenza virus strains with a fusion threshold of pH 5.5 or lower are inhibited by amantadine. Brief report

Nineteen influenza virus strains were examined for susceptibility to amantadine-HCl (AMT) and for pH-thresholds of haemagglutinin-induced haemolysis. Whereas pH-thresholds below 5.5 were not seen in AMT-resistant strains, AMT-sensitive strains showed pH-thresholds either below or above 5.5.

Analysis of antigenic relationships among influenza virus strains using a taxonomic cluster procedure. Comparison of three kinds of antibody preparations

Hemagglutination inhibiting (HI) monoclonal antibody preparations (MA) were raised against six influenza A (H3N2) strains from the period 1977-1982. Twenty-three hybridomas were selected and titrated in HI assays against these strains and against 18 influenza A (H3N2) viruses isolated in The Netherlands during the seasons 1981-1982 and 1982-1983. Similar HI tests were performed with conventional post-infection ferret antisera and with ferret antisera adsorbed with heterologous strains of influenza A (H3N2) virus. The resulting serological data were subjected to a computerized taxonomic cluster procedure based on the Euclidean distance between viruses. With respect to the degree of separation between clusters the unadsorbed ferret antisera were inferior to the adsorbed antisera whereas the MA were superior to both. Our results demonstrate that computer programs based on numerical taxonomy can be helpful in processing large numbers of serological data and that MA are indispensable in epidemiological and diagnostic influenza studies.

Antigenic heterogeneity among influenza A(H3N2) field isolates during an outbreak in 1982/83, estimated by methods of numerical taxonomy

Fourteen influenza A(H3N2) field isolates, mainly obtained during the first weeks of the 1982/83 influenza epidemic in The Netherlands, and nine influenza A(H3N2) reference strains were examined by means of haemagglutination inhibition (HI) tests with 23 polyclonal ferret sera. The resulting HI patterns were subjected to various methods of numerical taxonomy using, among others, taxonomic distance and correlation between strains for resemblance coefficients. Marked differences between distance and correlation coefficients were found in strains which differed in avidity only. The field isolates could be divided into four groups in respect of their taxonomic resemblance to the reference strains. The same grouping was found for five of the field isolates by testing these against 200 human sera.

Changes in the morphology of influenza particles induced at low pH

At low pH influenza virus causes membrane fusion. This phenomenon is thought to reflect a part of the infection mechanism of the virus. To obtain more information on the effect of low pH on the virus, the change in morphology of influenza virus particles was studied by electron microscopy. Further, the degradation of haemagglutinin (HA) after trypsin digestion as a function of pH was studied by gel electrophoresis. The results showed that a threshold value existed below which both a change in morphology and an increase in trypsin sensitivity were observed. This threshold pH was found to be strain specific. A number of strains showed a heterogeneity in the particle population with respect to the threshold pH. The various subpopulations appeared to differ genetically. Virus particles with uncleaved precursor HA, HAo, were not effected by the low pH treatment.