Comparison of humoral immune responses to trivalent influenza split vaccine in young, middle-aged and elderly people

Knowledge, Beliefs and Attitudes towards the Influenza Vaccine among Future Healthcare Workers in Poland

The flu vaccine is the best treatment for avoiding the flu and its complications. The aim of the study was to evaluate the knowledge of the flu vaccine and attitude towards the influenza vaccine among medical students in four majors of study (Nursing, Midwifery, Pharmacy, and Public health) in all years of study. A total number of 1137 subjects took part in the study. Most of the vaccinated students assessed the flu vaccine positively (78.5%, 73.7%, 60.7%, and 65.1%, according to their respective majors) and reported that they did not get the flu during the period of vaccination (90.4%, 92.1%, 87.4%, and 97.7%, respectively). Therefore, 65% of the students of Pharmacy, 78% of Midwifery, and 83% of Nursing who were vaccinated once in the last three years recommended the influenza vaccination, and 100% of all students received a regular vaccination every year. The univariate and multivariate logistic regressions showed that a maximum of four factors had a significant impact on the students’ knowledge of the influenza vaccine. Knowledge about the flu vaccine was the highest among Pharmacy students and lowest among Public health students. Final-year students answered the questions better than the younger ones (p < 0.05). Their place of residence and flu vaccination status also appeared to influence their answers. Although all students demonstrated good knowledge of the flu vaccine and demonstrated positive attitudes towards the vaccine, their rate of immunization was low. Therefore, health promotion programs are needed to improve immunization coverage among medical students who are future healthcare workers.

The Effect of Influenza Vaccination History on Changes in Hemagglutination Inhibition Titers After Receipt of the 2015-2016 Influenza Vaccine in Older Adults in Hong Kong

BACKGROUND

Immune responses to influenza vaccination can be weaker in older adults than in other age groups. We hypothesized that antibody responses would be particularly weak among repeat vaccinees when the current and prior season vaccine components are the same.

METHODS

An observational study was conducted among 827 older adults (aged ≥75 years) in Hong Kong. Serum samples were collected immediately before and 1 month after receipt of the 2015-2016 quadrivalent inactivated influenza vaccine. We measured antibody titers with the hemagglutination inhibition assay and compared the mean fold rise from prevaccination to postvaccination titers and the proportions with postvaccination titers ≥40 or ≥160.

RESULTS

Participants who reported receipt of vaccination during either of the previous 2 years had a lower mean fold rise against all strains than with those who did not. Mean fold rises for A(H3N2) and B/Yamagata were particularly weak after repeated vaccination with the same vaccine strain, but we did not generally find significant differences in the proportions of participants with postvaccination titers ≥40 and ≥160.

CONCLUSIONS

Overall, we found that reduced antibody responses in repeat vaccinees were particularly reduced among older adults who had received vaccination against the same strains in preceding years.

Antibody Response to Influenza Vaccination in Nursing Home Residents and Healthcare Workers During Four Successive Seasons in Niigata, Japan

Objective:

To evaluate the antibody response to influenza vaccines in nursing home residents and healthcare workers (HCWs) and its relation to residents' functional and chronic disease status during four successive seasons.

Design:

Before-after study.

Setting:

Nine nursing homes during the 1998-1999 season and two during the 1999-2000, 2000-2001, and 2001-2002 seasons.

Participants:

Two hundred fifty-nine residents and 79 HCWs during the 1998-1999 season; 180 and 71, respectively, during the 1999-2000 season; 162 and 71, respectively, during the 2000-2001 season; and 153 and 79, respectively, during the 2001-2002 season.

Results:

Multivariate analysis indicated that the mean fold increase in the geometric mean titers (GMTs) of hemagglutination inhibition (HI) antibodies and the response rate (the proportion of vaccinées resulting in a significant, at least fourfold increase in antibody titer) were good and no significant differences occurred for almost all strains in both residents and HCWs. The GMTs of HI antibodies and the protection rate (the proportion of participants with HI antibody titers & 40) were increased in both residents and HCWs, but were significantly lower for almost all strains in residents than in HCWs. Furthermore, multivariate analysis indicated that subdivision of residents into three groups by level of daily activities and into four groups according to underlying diseases revealed only minor differences in immune responses.

Conclusions:

Antibody responses to the influenza vaccine were lower in residents than in HCWs. However, residents showed similar antibody responses regardless of their level of daily activity or underlying diseases.

The confounded effects of age and exposure history in response to influenza vaccination

Numerous studies have explored whether the antibody response to influenza vaccination in elderly adults is as strong as it is in young adults. Results vary, but tend to indicate lower post-vaccination titers (antibody levels) in the elderly, supporting the concept of immunosenescence-the weakening of the immunological response related to age. Because the elderly in such studies typically have been vaccinated against influenza before enrollment, a confounding of effects occurs between age, and previous exposures, as a potential extrinsic reason for immunosenescence. We conducted a four-year study of serial annual immunizations with inactivated trivalent influenza vaccines in 136 young adults (16 to 39 years) and 122 elderly adults (62 to 92 years). Compared to data sets of previously published studies, which were designed to investigate the effect of age, this detailed longitudinal study with multiple vaccinations allowed us to also study the effect of prior vaccination history on the response to a vaccine. In response to the first vaccination, young adults produced higher post-vaccination titers, accounting for pre-vaccination titers, than elderly adults. However, upon subsequent vaccinations the difference in response to vaccination between the young and elderly age groups declined rapidly. Although age is an important factor when modeling the outcome of the first vaccination, this term lost its relevance with successive vaccinations. In fact, when we examined the data with the assumption that the elderly group had received (on average) as few as two vaccinations prior to our study, the difference due to age disappeared. Our analyses therefore show that the initial difference between the two age groups in their response to vaccination may not be uniquely explained by immunosenescence due to ageing of the immune system, but could equally be the result of the different pre-study vaccination and infection histories in the elderly.

Enhanced immune responses by skin vaccination with influenza subunit vaccine in young hosts

Skin has gained substantial attention as a vaccine target organ due to its immunological properties, which include a high density of professional antigen presenting cells (APCs). Previous studies have demonstrated the effectiveness of this vaccination route not only in animal models but also in adults. Young children represent a population group that is at high risk from influenza infection. As a result, this group could benefit significantly from influenza vaccine delivery approaches through the skin and the improved immune response it can induce. In this study, we compared the immune responses in young BALB/c mice upon skin delivery of influenza vaccine with vaccination by the conventional intramuscular route. Young mice that received 5 μg of H1N1 A/Ca/07/09 influenza subunit vaccine using MN demonstrated an improved serum antibody response (IgG1 and IgG2a) when compared to the young IM group, accompanied by higher numbers of influenza-specific antibody secreting cells (ASCs) in the bone marrow. In addition, we observed increased activation of follicular helper T cells and formation of germinal centers in the regional lymph nodes in the MN immunized group, rapid clearance of the virus from their lungs as well as complete survival, compared with partial protection observed in the IM-vaccinated group. Our results support the hypothesis that influenza vaccine delivery through the skin would be beneficial for protecting the high-risk young population from influenza infection.

Quantitative review of antibody response to inactivated seasonal influenza vaccines

BACKGROUND

Seasonal influenza epidemics are associated with significant morbidity and mortality each year, particularly amongst young children and the elderly. Seasonal influenza vaccines have been available for decades, yet influenza remains a major public health threat in the US, sparking interest in studies evaluating the effectiveness of vaccination.

OBJECTIVES

We sought to identify determinants of serological responses to inactivated seasonal influenza vaccines including number of doses, adjuvant, and subject characteristics.

METHODS

We reviewed 60 articles published between 1987 and 2006. We used weighted multiple logistic regression and random-effects models to evaluate how seroconversion and seroprotection rates varied with host and vaccine factors.

RESULTS

Both children and seniors tended to have poorer immune responses compared to adults whereas use of adjuvant and a second vaccine dose tended to improve immune response. Pre-vaccination serological status had a large impact on the immune response to vaccination. We found substantial heterogeneity among studies, even with similar population settings and vaccination regimen.

CONCLUSIONS

Future studies should stratify their results by pre-vaccination serological status in an effort to produce more precise summary estimates of vaccine response.

Influenza vaccination for terminally ill cancer patients receiving palliative care: a preliminary report

CONTEXT

Cancer patients have impaired humoral and cellular immunity, and are more susceptible to infections; their immunological response is expected to be less effective than that of healthy people.

OBJECTIVES

To assess the immune response to influenza vaccine in terminally ill cancer patients in a home palliative care unit.

METHODS

During the fall of 2000-2001, 2005-2006, and 2006-2007, terminally ill cancer patients treated by our home palliative care unit were vaccinated against influenza with Vaxigrip(®). Blood samples were taken before and four weeks after vaccination. Influenza immunological response parameters accepted in the literature were calculated.

RESULTS

Eighteen terminal cancer patients were vaccinated against influenza strains predicted for that year; 13 completed the study. The other five patients died within less than a month from the time of vaccination. The serum protection rate increased from 15.4% before to 61.5% after vaccination, and the serum response rate was 53.8% for all the three strains of vaccination. Mean-fold increase was 24.9 for influenza A-H1N1, 15.4 for influenza A-H3N2, and 2.8 for influenza B. Geometric mean titer was increased for influenza A-H3N2 from 8.3 before vaccination to 159.4 after vaccination; for influenza A-H1N1 from 5.2 to 124.3, and for influenza B from 5.7 to 44.6.

CONCLUSION

The results indicate that influenza vaccination is probably effective and can be offered to terminally ill cancer patients with a life expectancy of about three months in a home care palliative care unit.

Exercise intensity does not influence the efficacy of eccentric exercise as a behavioural adjuvant to vaccination

Acute exercise prior to vaccination can improve the antibody response to influenza vaccination. However, both the optimal exercise protocol and the mechanisms underpinning this adjuvant effect remain unclear. The aim of the current study was to determine whether exercise intensity influenced the efficacy of the intervention. One hundred and sixty healthy young adults were randomly assigned to a resting control group or one of three intervention groups, who exercised at an intensity of 60%, 85%, or 110% of their pre-determined concentric one repetition maxima. The exercise groups performed 50 repetitions of the eccentric portion of both bicep curl and lateral raise movements. All participants then immediately received a reduced dose (50% recommended dose) influenza vaccine. Antibody titres to the three viral strains contained in the vaccine were measured at baseline and at 28 days post-vaccination. Compared to the control group, exercise enhanced the antibody response to the least immunogenic of the three strains (B/Florida). In addition, the exercise groups showed an augmented response to the A/Uruguay strain compared to control; however, this effect was observed only in men. The intervention had no effect on the antibody responses to the most immunogenic strain, A/Brisbane. Finally, antibody responses were unrelated to the intensity of the exercise bout. In conclusion, our findings provide further evidence of exercise as an adjuvant to enhance vaccination responses. The results further show that responses to the low-immunogenic antigens are particularly responsive to augmentation by acute eccentric exercise.

The effectiveness of national influenza vaccination policies for at-risk populations over 5 seasons in a Scottish general practice

AIM

To determine the effectiveness of serial influenza vaccination.

SCOPE

Studied in a Scottish GP population, the overall seroresponse rate increased with annual influenza vaccinations and after 5 years it increased from 45.1% to 93.3% for influenza virus A (H1) and from 48.4% to 98.3% for influenza virus A (H3). However, there was little boosting effect with further doses after becoming a seroresponder. The pre-vaccination titres were significantly higher in previous year's seroresponders compared to non-responders.

CONCLUSIONS

The policy of annual vaccination is supported by our data in order to increase the disappointing response rate after one dose. However, the lack of a boosting response with subsequent doses and the significant residual immunity after becoming a seroresponder suggests a prior serological immunity check in order to better direct the vaccine supply (in the years of no antigenic drift), to those who need it most.

Assessment of the immune response to trivalent split influenza vaccine in children with solid tumors

PURPOSE

To assess the immune response to influenza vaccine in children with solid tumors receiving chemotherapy or under the influence of chemotherapy.

METHODS

Forty-five children (aged 1-18) with solid tumors on chemotherapy or within 6 months of completion of chemotherapy were included in the study. The children received two doses of intramuscular trivalent split influenza vaccine with 1 month apart in November-December 2003 (children <4 age 0.25 ml; >4 age 0.5 ml). Antibody titer was detected in the pre-vaccination and 4-week post-vaccination sera by hemagglutination inhibition (HI) method. Immune responses were measured as protective, geometric mean titers (GMT), and fourfold rises in HI titers.

RESULTS

We revealed that the post-vaccination GMT for each of the three antigens in patients with solid tumors has increased significantly (P < 0.05). A fourfold rise in the percentage of post-vaccination antibody titers has been detected as 84.4% for H(1)N(1), 77.8% for H(3)N(2), 60% for B. Stratification of patients as on active chemotherapy or being within 6 months of completion of chemotherapy in terms of fourfold rise in antibody titers exposed a statistically significant difference for only B (P = 0.34). Post-vaccination protective rates were between 86 and 97%.

CONCLUSIONS

Due to the interruptions in treatment caused by influenza infections, and economic benefits of the vaccine, we suggest that inactivated influenza vaccine should be applied as two doses annually in patients with solid tumor.

Antibody response to influenza vaccination in splenectomized patients in Poland

The aim of this study was to assess antibody response in 62 splenectomized patients and in 55 healthy subjects vaccinated with split influenza vaccine ("Fluarix," SmithKline Beecham). Response to hemagglutinin and neuraminidase was assessed before vaccination and after 1 month by hemagglutination inhibition test and neuraminidase inhibition test. After vaccination, antibody titers significantly increased in both groups. Postvaccination protection rates ranged from 62.9 to 90.3% in the splenectomized patients and from 81.8 to 94.5% in the control group. Response rates ranged from 50.0 to 75.8% and from 60.0 to 70.9%, respectively. Splenectomized patients produced high antibody levels regardless of the time elapsed from the operation to the vaccination. All requirements of the Committee for Proprietary Medicinal Products regarding humoral response to influenza vaccination in healthy people were fulfilled in both groups. The response in the splenectomized patients was comparable to that in the control group.

Response to influenza vaccination in community and in nursing home residing elderly: relation to clinical factors

Intramuscular (IM) influenza vaccines are about 50% effective in preventing respiratory illness among the elderly. The aim of this study was to identify factors associated with immune response to influenza vaccination among nursing home and community-residing elderly. 114 nursing home (NHE) and 62 community residing elderly (CE) were vaccinated with a commercial IM vaccine. Serum antibodies were evaluated by HIA, and the impact of subjects' clinical characteristics on seroconversion was determined. Factors that were associated with low seroconversion among NHE, included: type II diabetes [for B/Harbin: p=0.044, OR 0.12, (CI: 0.015-0.94)], and antibody titer prior to vaccination A/(H1N1): p=0.03, OR 2.38, (CI: 1.09-5.22); A/(H3N2): p=0.015, OR 2.68 (CI: 1.22-5.92), B/Harbin: p=0.057, OR 4.46 (CI: 0.96-20.85)]. Factors that were associated with lower seroconversion CE elderly, included older age [A/(H1N1): p=0.008, OR 0.846, (CI 0.75-0.96), B/Harbin: p=0.016, OR 0.812, (CI:0.69-0.96)], and antibody titer prior to vaccination A/(H1N1): p=0.029, OR 4.08, (CI: 1.16-14.37); A/(H3N2): p<0.0001, OR 11.495 (CI: 3.18-41.55)]. There was no significant difference in seroconversion between nursing home residing elderly and community elderly. We conclude that Type-II diabetes and antibody titer>1:40 prior to vaccination are associated with reduced response to the influenza vaccination in nursing home elderly.

Temporal surveillance of the humoral immunity against influenza vaccine in the elderly over 9 consecutive years

BACKGROUND

The effect of age on declining immunity is well established, but its influence on humoral responses to influenza vaccines is still debated.

OBJECTIVE

To compare prospectively the immunogenicity of an influenza vaccine in elderly and healthy control subjects and to search for correlations between this specific humoral protection and clinical and virological parameters.

METHODS

A prospective study of the humoral response to influenza vaccine was conducted over 9 consecutive years in the long-term care units of the Saint-Etienne University Hospital, France. Antibodies directed against the vaccinal strains in an inactivated trivalent vaccine were tested by radial haemolysis before and 1 month after 477 and 242 cumulative annual vaccinations in elderly people and in healthy controls, respectively. During the last 6 years of the study, clinical samples from patients with fever > or =38 degrees C were tested systematically for the diagnosis of an influenza infection.

RESULTS

A significant rise in anti-A/H3N2 antibody titres was observed in 49.3% of the elderly subjects and in 48.3% of the controls (not significant). The rises for the A/H1N1 and B strains were 31.4 and 39.2% (p < 0.001) and 30.6 and 40.5 (p < 0.001), respectively. When control subjects under 31 years old were excluded, no significant difference was recorded for any strain. Only 3.9% of the vaccinated elderly experienced any clinical influenza infection as defined by fever >/=38 degrees C and virological proof.

CONCLUSIONS

The humoral response to influenza immunization is not impaired in the elderly compared with middle-aged controls, and the incidence of febrile episodes due to influenza is low in this vaccinated elderly population. These findings provide further evidence supporting the recommendation for annual influenza vaccination in the elderly.

Immune response to influenza vaccination in an elderly population

The purpose of this study was to assess the serum antibody responses to both the hemagglutinin and the neuraminidase antigens of inactivated influenza vaccine in 45 elderly and 28 younger adults. After vaccination, antihemagglutinin antibody levels increased significantly and mean fold increases ranged from 2.8 to 22.0. Seroprotection rates were between 42.2 and 91.1% 1 month after vaccination and 15.6 and 84.4% 5 months afterward. Seroresponse rates ranged from 42.2 to 91.1% 1 month after vaccination and 15.6 to 82.2% 5 months afterward. After vaccination antineuraminidase antibody levels increased significantly and mean fold increases ranged from 3.6 to 12.3. Significantly higher antibody responses to both hemagglutinin and neuraminidase were observed for antigen A(H3N2) than for antigens A(H1N1) and B. In most instances there were no statistically significant differences between the elderly and the control subjects. Influenza vaccine was immunogenic in the institutionalized elderly, who developed good antibody responses to influenza hemagglutinin and neuraminidase antigens.

Local and systemic immune response in nursing-home elderly following intranasal or intramuscular immunization with inactivated influenza vaccine

Intramuscular (IM) influenza vaccines are only 30-40% effective in preventing clinical illness among the elderly, and their effectiveness in eliciting mucosal response may be even lower. The aim of the present study was to evaluate the immunological effect of a novel inactivated intranasal (IN) trivalent whole influenza virus vaccine among nursing-home elderly. Twenty-one institutionalized elderly subjects were vaccinated IN with an inactivated novel vaccine, twice, 21 days apart, and with no adverse effects. Twenty-two subjects were vaccinated once with a commercial IM vaccine. Viral strains used in the 1998/9 vaccine (20 microg of each per dose) were A/Beijing/262/95, A/Sydney/5/97 and B/Harbin/7/94. Serum antibodies (IgG and IgM) and nasal IgA were determined by the hemagglutination inhibition (HI) test and enzyme-linked immunosorbent assay (ELISA), respectively. Mucosal antibody response to the three vaccine strains was detected in 47.6-71.4% and 18.1-31.8% of IN and IM immunized subjects, respectively. Serum antibody response to the three antigens tested was detected in 20.0-61.9% and 18.2-72.7% of IN and IM immunized subjects, respectively. Seroconversion was not significantly different after IN or IM vaccination for both A/Sydney and B/Harbin, but higher for A/Beijing following IM vaccination. On study completion, 57.1, 65.0 and 50.0% of IN vaccinees were seroprotected to A/Beijing, A/Sydney and B/Harbin, respectively. Similarly, 68.1, 77.2 and 54.5% were immune after IM vaccination. The IN vaccine tested was significantly more effective than the IM vaccine in inducing mucosal IgA response. This may prevent influenza at its early stages and thus contribute to the reduction of morbidity and complications in nursing-home elderly.

Nosocomial influenza infection among post-influenza-vaccinated patients with severe pulmonary diseases

OBJECTIVES

To report an outbreak of nosocomial influenza in thirteen out of twenty-two admitted patients suffering from severe lung emphysema.

METHODS

Acute-phase and convalescent serum samples of nine patients were collected. An antihaemagglutinin assay was performed to detect a rise in antibodies against influenza A virus. Further information about vaccination history of the patients and healthcare workers was included.

RESULTS

The majority of these twenty-two patients was vaccinated with a trivalent vaccine six months earlier. The immunological response showed that the influenza A (H3N2) strain which caused these infections is similar to the vaccine strain A/Sydney/5/97.

CONCLUSIONS

The staff of our institute which was not systematically vaccinated may have been the source of infection. The time elapsed between the vaccination and the infection is the probable explanation of this event.

Efficacy of subunit trivalent influenza vaccine in previously vaccinated children suffering from hemophilia

OBJECTIVE: To assess humoral immune response to subunit trivalent influenza vaccine in children suffering from hemophilia who had been immunized for the first time in 1993-94 and then in 1996-97. METHODS: In autumn 1996-97, 38 previously vaccinated hemophiliac patients were subcutaneously immunized with a single 0.5-mL dose of subunit influenza vaccine containing the following three virus strains: A/Singapore/6/86 (H1N1), A/Wuhan/359/95 (H3N2) and B/Beijing/184/93 (HB). Antibody response to influenza vaccine was measured before vaccination, 3 weeks after vaccination and 6 months after vaccination, by use of hemagglutinin- and neuraminidase-inhibition tests. To present the level of seroconversion, geometric mean titers of anti-influenza antibodies, mean fold increase, protection rate and conversion rate were determined. All results were compared with the control group of 23 healthy persons who had never been vaccinated against influenza and for whom the same serologic tests were carried out as for the vaccinated group. RESULTS: Three weeks after immunization, antihemagglutinin antibody levels were 3.9-10.9 times higher than before vaccination, but the highest mean fold increase values were recorded 6 months after vaccination, ranging from 8.4 to 28.6. In the case of neuraminidase, mean fold increases of antibodies reached values of 3.6-12.3 three weeks after vaccination and 7.1-29.1 six months after vaccination. The highest proportion of subjects protected was observed 6 months after immunization and ranged from 76.3% to 97.4%, compared to 52.6-60.5% 3 weeks after vaccination. Similar values were obtained for conversion rate: 71.1-86.8% 6 months after vaccination, in comparison with 39.5-42.1% 3 weeks after immunization. CONCLUSIONS: All data obtained in the present study indicate a significant immune response to subunit trivalent influenza vaccine in patients suffering from hemophilia; this is additionally confirmed by the fact that none of the vaccinated children were infected with the influenza virus and no serious adverse reactions were observed after administration of the vaccine.

Characterization of antibody responses to annual influenza vaccination over four years in a healthy elderly population

The effects of yearly influenza immunization on the level of antibody responses were assessed in 92 healthy elderly subjects immunized over four contiguous years (1993-1996) with a trivalent influenza vaccine that included A/Texas annually. Anti-A/Texas antibodies increased significantly and similarly post-vaccination each year, but returned to comparable baseline levels annually. Percentages of subjects with anti-A/Texas titers > or =40 post-vaccination were comparable over four years. Importantly, post-vaccination titers > or =40 to A/Texas in 1993-1994 predicted anti-A/Texas titers > or =40 in subsequent years. Thirty percent of individuals produced four-fold rises to any vaccine component the first year it was included in the vaccine, however, this percentage decreased to about 10% after subsequent vaccination with the same component. This study clearly supports the concept that annual immunization with the same influenza vaccine component over multiple years does not significantly decrease antibody titers in a healthy elderly population.

Antibody response after influenza vaccination in HIV-infected individuals: a consecutive 3-year study

In a consecutive 3-year study the antibody response after immunization with influenza vaccine of a cohort of HIV-infected adults was studied. The haemagglutination-inhibiting (HAI) antibody titres after vaccination correlated with the number of CD4(+) T lymphocytes (p<0.001), the prevaccination antibody titres (p<0.001), and the proliferative response to anti-CD3 (p<0.001). Severely impaired antibody responses were observed in HIV-infected individuals with CD4(+) T-lymphocyte counts < or =100x10(6)/l. Significantly higher prevaccination antibody titres were observed in healthy controls in the 2nd or 3rd year of vaccination, but not in HIV-infected individuals. Annually repeated vaccination of HIV-infected individuals did not lead to higher postvaccination antibody titres. Annual vaccination of HIV-infected individuals with CD4(+) T-lymphocyte counts exceeding 100x10(6)/l seems to be worthwhile, although it may not be expected to render the same level of protection against influenza as in non-infected individuals.

Humoral immune response to influenza vaccination in patients from high risk groups

Influenza is one of the most common respiratory diseases. Infections caused by this virus may be very serious and can lead to severe complications. So far, the most effective method of protection against influenza is annual vaccination. The Advisory Committee on Immunisation Practices recommends vaccination against influenza for some groups of people. Unfortunately, in spite of these clear indications, a large number of patients are not vaccinated. This article reviews the current scientific literature on immunological response to influenza vaccination in patients who are at especially high risk for serious post-influenza complications and for whom immunisation against this virus is strongly recommended. Results of studies carried out in Poland and other countries in elderly people, in patients with pulmonary diseases, renal diseases, diabetes mellitus, cancer and haemophilia, and in those with HIV infection are presented. In this review, we focus on the immune response to haemagglutinin. There are some discrepancies between the results of studies carried out by different authors in high risk groups of patients. Some investigations indicated poorer humoral response to influenza vaccine in these groups, while others showed responses comparable to those in healthy individuals. These differences may be explained by differences in types and stages of the chronic diseases, in the treatment and composition of influenza vaccines, and also patients' ages, vaccination history and prevaccination antibody titres. Influenza vaccines are well tolerated in high risk patients, and all adverse reactions are generally mild and similar to those observed in healthy people. Although, in some cases, immunological responses to influenza vaccination measured in the whole study group were poor, there were some individual patients who, after vaccination, developed antihaemaglutinin antibody titres which are considered to give protection against the infection or contribute to a milder course of the disease.

Respiratory viral infections in the elderly

Viral respiratory infections represent a significant challenge for those interested in improving the health of the elderly. Influenza continues to result in a large burden of excess morbidity and mortality. Two effective measures, inactivated influenza vaccine, and the antiviral drugs rimantadine and amantadine, are currently available for control of this disease. Inactivated vaccine should be given yearly to all of those over the age of 65, as well as younger individuals with high-risk medical conditions and individuals delivering care to such persons. Live, intranasally administered attenuated influenza vaccines are also in development, and may be useful in combination with inactivated vaccine in the elderly. The antiviral drugs amantadine and rimantadine are effective in the treatment and prevention of influenza A, although rimantadine is associated with fewer side-effects. Recently, the inhaled neuraminidase inhibitor zanamivir, which is active against both influenza A and B viruses, was licensed for use in uncomplicated influenza. The role of this drug in treatment and prevention of influenza in the elderly remains to be determined. Additional neuraminidase inhibitors are also being developed. In addition, to influenza, respiratory infections with respiratory syncytial virus, parainfluenza virus, rhinovirus, and coronavirus have been identified as potential problems in the elderly. With increasing attention, it is probable that the impact of these infections in this age group will be more extensively documented. Understanding of the immunology and pathogenesis of these infections in elderly adults is in its infancy, and considerable additional work will need to be performed towards development of effective control measures.

Two outbreaks of influenza A (H3N2) in a Japanese nursing home in the winter of 1996-1997, with differing vaccine efficacy

Sixty of 128 (46.9%) residents of a nursing home were immunized with two doses of the trivalent split influenza vaccine. They developed 7.4-11.5-fold antibody increases, with a 69-82% protection rate, presenting good immune response rates to the influenza vaccine. Two outbreaks of influenza A (H3N2) occurred. There were no significant antigenic differences among the vaccine strain and the strains isolated from both outbreaks in haemagglutination-inhibition tests, suggesting that the second might have been a reoccurrence. There were no residents who were infected in both outbreaks. The vaccine efficacy against clinical illness in the first outbreak of typical influenza-like-illness (ILI) was 51% (relative risk: 0.49), and the febrile period was reduced significantly by vaccination. In the second outbreak, however, in which all patients had atypical ILI with a high fever but not respiratory symptoms, vaccine efficacy was not apparent for unknown reason.

Influenza vaccines: antibody responses to split virus and MF59-adjuvanted subunit virus in an adult population

The humoral immune response generated by two commercial influenza vaccines was evaluated in a randomised, double-blind trial performed in the Public Department of Dolo Health District (North-east Italy) during the winter season 1997-1998. Ninety-eight subjects were immunised with a split virus vaccine and ninety-six with a MF59-adjuvanted subunit virus vaccine (SU/MF59). The pre- and postvaccination (approximately 30 days) antibody titres were determined by hemagglutination inhibition test (HI). After immunisation protective titre rates (> or = 1:40) were near 100% against virus A strain and 82.5% against B strain. Both vaccines caused significant rises in geometric mean antibody titres (GMTs); however, people who received SU/MF59 vaccine were found to develop a greater immune response compared to the group immunised with SVV. According to logistic regression analysis the unprotective prevaccination immune status and the use of SU/MF59 were identified as independent factors significantly increasing the response to immunisation.

Dose-dependent antibody response to influenza H1N1 vaccine component in elderly nursing home patients

The effects of an increased antigen dose on HI, IgG, IgA, and IgM antibody responses to influenza A/Taiwan/1/86 (H1N1) were investigated in 92 elderly nursing-home residents (mean age 81 years) and 104 young subjects (mean age 20 years). At a standard 10-microg dose, HI and IgG titer rises were lower in the elderly. HI titers did not improve at higher vaccine dosages. By contrast, influenza-specific IgG and IgA antibody responses were dose dependent in elderly subjects, but not in young. In the young subjects, IgM antibody responses were dose dependent. The improved antibody responses in the elderly as observed in IgG and IgA were not reflected in the HI response. Therefore, the evaluation of antibody production by HI only may lead to an underestimate of the immune response in elderly people.

Immunogenicity of influenza vaccine in patients with hemato-oncological disorders

The aim of this study was to measure the production of antihemagglutinin and antineuraminidase antibodies in patients with proliferative diseases of the hematopoietic or lymphatic system, immunized with influenza vaccine in the epidemic season 1995/96. Twenty patients between 22 and 84 years volunteered for vaccination and were vaccinated subcutaneously with a single dose of split trivalent influenza vaccine ("Fluarix", SmithKline Beecham) in autumn 1995 at the outpatients clinic, General Hospital, Toruń, Poland, where they were being treated with anti-cancer chemotherapy. The vaccine consisted of a 0.5 ml dose containing 15 microg hemagglutinin (HA) of each of the following strains: A/Singapore/6/86 (H1N1), A/Johannesburg/33/94 (H3N2) and B/Beijing/184/93. Neuraminidase activity amounted to 17.24x10(-3) U/ml. Antibody production was determined in sera collected before vaccination, 10 days and 28 days after vaccination by the hemagglutinin inhibition test (HI) and neuraminidase inhibition test (NI). Mean fold increase values after vaccination were statistically significant in patients undergoing cytostatic treatment. After 28 days mean fold increase of antihemagglutinin antibodies ranged from 7.9 to 25.2, while in the case of antineuraminidase antibodies these values were between 12.4 and 14.3. It is notable that no adverse reactions were observed after immunization and none of the patients was infected with influenza virus, in spite of the fact that there was a local epidemic in the Toruń region when the study was carried out. The results presented in this paper confirm the beneficial effect of influenza vaccination in high-risk groups of patients with proliferative diseases of the hematopoietic and lymphatic systems.

Altered antibody response to influenza H1N1 vaccine in healthy elderly people as determined by HI, ELISA, and neutralization assay

To determine the influence of ageing per se as well as of priming histories on the antibody response to influenza vaccination, haemagglutination inhibition (HI), ELISA IgG, IgA, IgM and neutralizing antibody titres were studied in 43 healthy young subjects (mean age 23 years) and 55 healthy elderly people (mean age 79 years). The HI and ELISA lgG responses to the A/Guizhou/54/89 strain (H3N2) for which both the young and the elderly had similar priming histories were equal. By contrast, the HI and IgG responses to A/Taiwan/1/86 (H1N1), where the priming histories were different, were lower in the elderly (P < 0.05). Influenza-specific IgA responses in the elderly tended to be higher for all vaccine strains. Influenza-specific postvaccination IgM titres were similar or tended to be higher in the elderly. A subgroup of elderly subjects (18%) who did not express HI activity to the A/Taiwan/1/86 (H1N1) vaccine strain, reacted in the HI assay with the closely related A/Singapore/6/86 (H1N1) strain. These elderly people, however, produced lgG antibodies which neutralized A/Taiwan/1/86 virus in vitro. It is concluded that the elderly are capable of mounting antibody responses similar to those observed in the young. Moreover, the observed age-related differences in antibody responses to H1N1 strains are probably not due to ageing of the immune system itself, but are determined by differences in priming histories.

Immunogenicity of subunit trivalent influenza vaccine in children with acute lymphoblastic leukemia

BACKGROUND

The aim of this study was to assess humoral response to influenza vaccine in children with acute lymphoblastic leukemia.

METHODS

Studies were performed in 25 patients previously vaccinated against influenza (Group A) and in 20 children who had never been immunized before (Group B). In Autumn, 1996, they were vaccinated with subunit trivalent influenza vaccine containing 15 microg of hemagglutinin of A/Singapore/6/86, A/Wuhan/359/95 and B/Beijing(184/93. Antihemagglutinin (HI) and antineuraminidase antibody titers were determined before immunization and 3 weeks and 6 months after vaccination by the hemagglutinin inhibition test and the neuraminidase inhibition test. All results were presented as the geometric mean titer of antibodies, mean fold increase of antibody titer, protection rate and response rate.

RESULTS

In Group A mean fold increase of HI antibodies ranged from 17.2 to 26.7 three weeks after vaccination and from 22.1 to 38.2 six months after vaccination, while in Group B it ranged from 15.7 to 22.6 and from 30.3 to 39.3, respectively. In the case of neuraminidase, mean fold increases for Group A varied from 9.2 to 13.2 three weeks after immunization and from 15.6 to 21.1 six months after vaccination, whereas for Group B they varied from 5.5 to 8.3 and from 14.4 to 23.4, respectively. Six months after vaccination the proportion of subjects with HI antibodies > or = 1:40, as well as those with at least 4-fold increase of HI antibody titers, ranged from 68 to 100% in Group A and from 90 to 100% in Group B. No vaccinated child was infected with the influenza virus; the vaccine was well-tolerated and did not cause any adverse reactions.

CONCLUSIONS

The results obtained in this study indicate that influenza vaccine is immunogenic in patients with acute lymphoblastic leukemia, despite their serious disease.

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.

Kinetics of humoral response in children with acute lymphoblastic leukemia immunized with influenza vaccine in 1993 in Poland

A total of 49 children with acute lymphoblastic leukemia were immunized with a purified subvirion trivalent influenza vaccine (Wyeth-USA) and monitored for hemagglutination inhibition (HI) and neuraminidase inhibition (NI) antibodies before vaccination, and then three weeks and six months after vaccination. Results for HI antibodies were evaluated as geometric mean titre (GMT), mean fold antibody increase (MFI), protection and response rates and those for NI antibodies as geometric mean titre (GMT) and mean fold antibody increase (MFI). Six months after vaccination GMT for hemagglutinin 1 (H1) was much higher than previous values. GMT for hemagglutinin 3 (H3) and hemagglutinin B (HB) was lower than three weeks after vaccination, but much higher than the original values. In the control group GMT for H1 was on a low level all the time and for H3 and HB it was lower when compared with the original values. The proportion of vaccines to antibodies > or = 40 ranged between 45% and 88%. Six months after vaccination GMT for neuraminidase 1 (N1) increased when compared with the second sampling; for neuraminidase 2 (N2) and neuraminidase B (NB) it was slightly lower. In the control group GMT for all antigens was on a low level all the time. The results point to a significant seroconversion for both components after vaccination when compared with the control group.

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.

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.

DHEAS as an effective vaccine adjuvant in elderly humans. Proof-of-principle studies

We have demonstrated that in aged mice, the titer of serum antibody induced against tetanus toxoid correlates with resistance to local paralysis caused by injection of tetanus toxin. Only mice immunized shortly after oral dosing with DHEAS demonstrated high serum antibody titers and complete protection from paralysis. These results became the basis for initiating proof-of-principle studies in human volunteers above age 65 using a licensed influenza vaccine and tetanus toxoid in two independent studies. The use of an oral delivery form of DHEAS before influenza vaccination was associated with a demonstrable increase in the number of individuals with a fourfold increase in HAI titers following vaccination. The overall mean increase in HAI titers was highest in the DHEAS-treated group. The use of DHEAS in the immunization of elderly subjects against tetanus toxoid, while unable to enhance the responses, was not a detriment to antibody response. We conclude that further studies will justify the use of DHEAS as an adjuvant for antigens that represent primary responses in the elderly.

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.

Immunogenicity of new virosome influenza vaccine in elderly people

The safety and immunogenicity of a new virosome influenza vaccine was compared to commercial whole-virus vaccine and subunit vaccine in elderly people. The virosome vaccine was made by extracting the haemagglutinin from influenza virus and incorporating it into the membrane of liposomes composed of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). 126 residents of a nursing home, aged 63-102, were randomised to receive one of the vaccines. All three were well tolerated and caused a significant rise in the geometric mean anti-haemagglutinin inhibiting (HAI) antibody titre to the 3 vaccine components (H1N1 Singapore, H3N2 Beijing, and B/Yamagata). The virosome formulation caused the highest geometric mean titres in addition to significantly (p = 0.039-0.0016) higher rates of more than four-fold or more titre rises to all 3 vaccine components. The percentage of those immunised who achieved protective levels of antibody (HAI > or = 40) was significantly (p = 0.035-0.0017) higher for the H1N1 and B/Yamagata strains following immunisation with virosome formulation. Participants with non-protective baseline titres to the H1N1 or B/Yamagata strains were more likely (p = 0.0049-0.006) to achieve protective levels of antibodies after immunisation with the virosome vaccine. Immunisation with the virosome formulation did not result in a significant rise in anti-PC or anti-PE antibodies.