Serological response to influenza A H1N1 vaccine (Pandemrix®) and seasonal influenza vaccine 2009/2010 in renal transplant recipients and in hemodialysis patients

Similar severity of influenza primary and re-infections in pre-school children requiring outpatient treatment due to febrile acute respiratory illness: prospective, multicentre surveillance study (2013-2015)

Background

Influenza virus infections in immunologically naïve children (primary infection) may be more severe than in children with re-infections who are already immunologically primed. We compared frequency and severity of influenza virus primary and re-infections in pre-school children requiring outpatient treatment.

Methods

Influenza-unvaccinated children 1–5 years of age presenting at pediatric practices with febrile acute respiratory infection < 48 h after symptom onset were enrolled in a prospective, cross-sectional, multicenter surveillance study (2013–2015). Influenza types/subtypes were PCR-confirmed from oropharyngeal swabs. Influenza type/subtype-specific IgG antibodies serving as surrogate markers for immunological priming were determined using ELISA/hemagglutination inhibition assays. The acute influenza disease was defined as primary infection/re-infection by the absence/presence of influenza type-specific immunoglobulin G (IgG) and, in a second approach, by the absence/presence of subtype-specific IgG. Socio-demographic and clinical data were also recorded.

Results

Of 217 influenza infections, 178 were due to influenza A (87 [49%] primary infections, 91 [51%] re-infections) and 39 were due to influenza B (38 [97%] primary infections, one [3%] re-infection). Children with “influenza A primary infections” showed fever with respiratory symptoms for a shorter period than children with “influenza A re-infections” (median 3 vs. 4 days; age-adjusted p = 0.03); other disease characteristics were similar. If primary infections and re-infections were defined based on influenza A subtypes, 122 (87%) primary infections (78 “A(H3N2) primary infections”, 44 “A(H1N1)pdm09 primary infections”) and 18 (13%) re-infections could be classified (14 “A(H3N2) re-infections” and 4 “A(H1N1)pdm09 re-infections”). Per subtype, primary infections and re-infections were of similar disease severity. Children with re-infections defined on the subtype level usually had non-protective IgG titers against the subtype of their acute infection (16 of 18; 89%). Some patients infected by one of the influenza A subtypes showed protective IgG titers (≥ 1:40) against the other influenza A subtype (32/140; 23%).

Conclusions

Pre-school children with acute influenza A primary infections and re-infections presented with similar frequency in pediatric practices. Contrary to expectation, severity of acute “influenza A primary infections” and “influenza A re-infections” were similar. Most “influenza A re-infections” defined on the type level turned out to be primary infections when defined based on the subtype. On the subtype level, re-infections were rare and of similar disease severity as primary infections of the same subtype. Subtype level re-infections were usually associated with low IgG levels for the specific subtype of the acute infection, suggesting only short-time humoral immunity induced by previous infection by this subtype. Overall, the results indicated recurring influenza virus infections in this age group and no or only limited heterosubtypic antibody-mediated cross-protection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06988-7.

Epidemiology of laboratory-confirmed influenza among kidney transplant recipients compared to the general population-A nationwide cohort study

Seasonal influenza causes morbidity and mortality after organ transplantation. We quantified the detection of laboratory-confirmed influenza among kidney transplant recipients compared to the general population in a nationwide cohort. All laboratory-confirmed cases of influenza and hospitalizations due to influenza among all kidney transplant recipients in our country between 1995 and 2017 were captured with database linkage from statutory national registries. Data from the general population of Finland, population 5.5 million, were used for comparisons. Annual incidences of influenza and hospitalizations due to influenza, and standardized incidence ratios (SIR) were calculated. Altogether 3904 kidney transplant recipients with a total follow-up of 37 175 patient-years were included. Incidence of laboratory-confirmed influenza was 9.0 per 1000 patient years in 2003-2019, and 18.0 per 1000 patient years during 2015-2019. The risk of laboratory-confirmed influenza was significantly higher among kidney transplant recipients compared to the general population (SIR 5.1, 95% CI 4.5-5.7). SIR for hospitalization due to influenza was 4.4 (95% CI 3.4-4.7). Mortality of the hospitalized patients was 9%, and 5% of the patients with laboratory-confirmed influenza. Detection of laboratory-confirmed influenza is increased fivefold and risk of hospitalization due to influenza more than fourfold among kidney transplant recipients compared to the general population.

Humoral Response to SARS-CoV-2-Vaccination with BNT162b2 (Pfizer-BioNTech) in Patients on Hemodialysis

mRNA-based SARS-CoV-2 vaccines offer a preventive strategy against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections that is of interest in the care of patients on hemodialysis (HDP). We measured humoral immune responses in 72 HDP after standard vaccination with two doses of the mRNA-based SARS-CoV-2 vaccine BNT162b2 (Pfizer-BioNTech). Antibody responses were evaluated with an anti-SARS-CoV-2 IgG ChemiLuminescent ImmunoAssay (CLIA) two weeks after the second dose. In addition, SARS-CoV-2 IgG was determined in a control of 16 healthy healthcare workers (HCW). The control group of HCW has shown a strong antibody response with a median (MD (Q1; Q3)) antibody titer of 800.0 AU/mL (520.5; 800.0). In comparison to HCW, HDP under 60 years of age responded equally (597.0 AU/mL (410.5; 800.0), p = 0.051). However, the antibody responses of the HDP negatively correlated with age (r2 = 0.2954 p < 0.0001), leading to significantly lower antibody titers in HDP over 60 years (280.0 AU/mL (45.7; 477.0), p < 0.0001). To thoroughly understand the immunogenicity of the new mRNA-based vaccines in HDP, longitudinal data on the effectiveness and durability of antibody responses are needed. Modifications of immunization schedules should be considered in HDP with low or without antibody responsiveness after standard vaccination to boost immune reactivity and prolong protective effects in these vulnerable patients.

High-Dose Seasonal Influenza Vaccine in Patients Undergoing Dialysis

BACKGROUND AND OBJECTIVES

High-dose influenza vaccine, which contains fourfold more antigen than standard dose, is associated with fewer cases of influenza and less influenza-related morbidity in the elderly general population. Whether the high-dose influenza vaccine benefits patients on dialysis, whose immune response to vaccination is less robust than that of healthy patients, is uncertain.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We compared hospitalizations and deaths during the 2015-2016 and 2016-2017 influenza seasons by vaccine type (standard trivalent, standard quadrivalent, and high-dose trivalent influenza vaccine) administered within a national dialysis organization. The association of vaccine type with outcomes was estimated using Cox proportional hazards regression with adjustment for patient factors and "center effect." Analyses were stratified by age and dialysis modality.

RESULTS

Between September 1 and December 31, 2015, standard dose trivalent, standard dose quadrivalent, and high-dose trivalent influenza vaccines were administered to 3057 (31%), 5981 (61%), and 805 (8%) patients, respectively. The adjusted rates of first hospitalizations by vaccine type during the influenza season were 8.43, 7.88, and 7.99 per 100 patient-months, respectively, and the adjusted rates of death were 1.00, 0.97, and 1.04, respectively. These differences were not significant. In 2016, 3614 (39%) received quadrivalent vaccine, and 5700 (61%) received high-dose trivalent vaccine. The adjusted rates of first hospitalization by vaccine type were 8.71 and 8.04 per 100 patient-months, respectively, and the adjusted rates of death were 0.98 and 1.02, respectively. Receipt of high dose was associated with a significant reduction in hospitalization (hazard ratio, 0.93; 95% confidence interval, 0.86 to 1.00; P=0.04); there was no significant association with death. There was no significant heterogeneity of either association by age group or dialysis modality.

CONCLUSIONS

Receipt of high-dose compared with standard dose influenza vaccine in 2016-2017 was associated with lower rates of hospitalization in patients on dialysis, although that was not seen in 2015-2016.

Vaccination practices in dialysis patients: A narrative review

In a period of turmoil concerning vaccination practices, there is a serious conflict between scientifically reasonable, evidence-based guidelines and the far-fetched rumors or misconceptions concerning the vaccination practices in the general population. When a significant portion of the medical and paramedical personnel may be deliberately unvaccinated against common biological agents, achieving effective vaccination rates in the dialysis population may be complicated. Vaccination rates are unacceptably low in dialysis patients and seroconversion rates are even lower; further, serological follow-up is generally poor. The particularly anergic immune system of the advanced chronic kidney disease patients is partly a cause of both high rates of infection and low rates of seroconversions. This narrative review is an effort to summarize current knowledge concerning the vaccination practices in dialysis patients with some specific recommendations based on these facts. Of particular interest is a new vaccine, the Zoster Recombinant, Adjuvanted Vaccine (Shingrix), which we will include in our discussion.

Clinical efficacy of seasonal influenza vaccination: characteristics of two outbreaks of influenza A(H1N1) in immunocompromised patients

BACKGROUND

Influenza A(H1N1) causes serious complications in immunocompromised patients. The efficacy of seasonal vaccination in these patients has been questioned.

AIM

To describe two outbreaks of influenza A(H1N1) in immunocompromised patients.

METHODS

Two outbreaks of influenza A(H1N1) occurred in our institution: on the kidney transplant ward in 2014 including patients early after kidney or simultaneous pancreas-kidney transplantation, and on the oncology ward in 2016 including patients receiving chemotherapy for malignant tumours. Factors leading to these outbreaks and the clinical efficacy of seasonal influenza vaccination were analysed.

FINDINGS

Altogether 86 patients were exposed to influenza A(H1N1) during the outbreaks, among whom the seasonal influenza vaccination status was unknown in 10. Only three out of 38 vaccinated patients were infected with influenza A(H1N1), compared with 20 out of 38 unvaccinated patients (P = 0.02). The death of one out of 38 vaccinated patients was associated with influenza, compared with seven out of 38 unvaccinated patients (P = 0.06). Shared factors behind the two outbreaks included outdated facilities not designed for the treatment of immunosuppressed patients. Vaccination coverage among patients was low, between 40% and 70% despite vaccination being offered to all patients free of charge. Vaccination coverage of healthcare workers on the transplant ward was low (46%), but, despite high coverage on the oncology ward (92%), the outbreak occurred.

CONCLUSION

Seasonal influenza vaccination was clinically effective with both a reduced risk of influenza infection and a trend towards reduced mortality in these immunocompromised patients. Several possible causes were identified behind these two outbreaks, requiring continuous awareness in healthcare professionals to prevent further outbreaks.

Changes of immunogenic profiles between a single dose and one booster influenza vaccination in hemodialysis patients - an 18-week, open-label trial

Annual influenza vaccination is recommended, but its efficacy in dialysis population is still controversial. Here we aimed to compare the dynamic changes of immune response between various influenza vaccination protocols in hemodialysis patients. A 18-week open label, non-randomized, controlled trial was conducted during 2011–2012. The efficacy between unvaccinated, one- and two-dose regimens were evaluated in 175 hemodialysis patients. Immunogenic profiles were assessed by hemagglutination-inhibition assays. At 3–9 weeks post-vaccination, antibody responses were similar between the one- and two-dose regimens, while the seroprotection rates (antibody titer ≥1:40) for influenza A were 55.6–82.5% in the adult (18–60 years) and 33.3–66.7% in the elderly (>60 years). Meanwhile, the seroprotection rates for influenza B were low (4.0–25.0%). By 18 weeks post-vaccination, the seroprotection rates for influenza A and B declined (0.0–33.3%) in both the adult and elderly receiving one- or two-dose regimens. Of dialysis patients, at most 2.4% developed moderate to severe adverse effects(myalgia and headache) after vaccination. In conclusion, the two-dose regimen could not improve immune responses than the one-dose regimen in hemodialysis patients; meanwhile the induced protective antibodies of both regimens could not be maintained for more than 4 months. Modification of current influenza vaccination strategy in dialysis population should be re-considered.

Characterisation of nosocomial and community-acquired influenza in a large university hospital during two consecutive influenza seasons

BACKGROUND

Nosocomial influenza is increasingly recognized as an important public health threat causing considerable morbidity and mortality each year. However, data on nosocomial influenza is usually collected during outbreaks only and clinical information of nosocomial influenza is sparsely available.

OBJECTIVES

To systematically analyse the distribution of nosocomial and community-acquired influenza and epidemiological characteristics in a tertiary care unit in two consecutive seasons.

STUDY DESIGN

A retrospective observational study was conducted to identify and characterise cases of nosocomial and community-acquired influenza at Freiburg University hospital from 1 January 2013 to 30 April 2014. A validated multiplex RT-PCR to detect influenza virus and other respiratory pathogens was used throughout. Clinical information was retrieved from the hospital-based information system.

RESULTS

Overall, 218 patients with laboratory-confirmed influenza were included (179 in the first, 39 patients in the second season). A rate of 20% of nosocomial influenza was observed throughout. A fatal outcome was recorded for 9% of nosocomial cases, which were mainly associated with influenza virus A(H1N1)pdm09. Nosocomial influenza occurred in all age groups, but fatalities were only observed in patients ≥18 years. Patients with nosocomial influenza were significantly older, underwent therapy for blood malignancies and immunosuppressive regimens more frequently, and received solid organ transplantation more often compared to community-acquired patients.

CONCLUSIONS

Despite the different distribution of virus subtypes and epidemiological properties between both influenza seasons, the rate of nosocomial cases remained similar. Systematic detection and targeted prevention measures seem mandatory to minimize nosocomial influenza.

Immunization in transplantation: review of the recent literature

PURPOSE OF REVIEW

Immunosuppressive treatments increase the life-long risk of solid organ transplant (SOT) recipients for severe infections, some of which are vaccine-preventable. In this review of the literature published during the last 15 months, we critically summarize vaccine-oriented articles in SOT candidates or recipients. Because of previously reported differences, vaccine-specific studies are needed for each type of SOT recipients.

RECENT FINDINGS

Thanks to new data gathered during the H1N1/2009 influenza pandemic, recent research mainly focused on influenza vaccination, especially in kidney transplantation. Lung transplantation, mycophenolate treatment, increasing age and end-stage organ failure were frequently identified as risk factors for nonresponse to immunization in general. New evidence concerning the safety of immunizing SOT recipients with live-attenuated vaccines is obtained.

SUMMARY

During this last year, more encouraging data have been published regarding safety and immunogenicity of vaccination in SOT recipients. New inventive strategies should be studied to overcome missed opportunities for vaccinating SOT candidates and recipients, and to promote the most effective vaccination schedule and follow-up.

Immunizations following solid-organ transplantation

PURPOSE OF REVIEW

To highlight the latest evidence for the use of key vaccines that are recommended in organ transplant candidates and recipients.

RECENT FINDINGS

Influenza vaccine is the best studied vaccine; factors affecting immunogenicity of this vaccine include time from transplant, use of mycophenolate mofetil and type of transplant. Newer formulations of influenza vaccine are available, but data for these are limited. Updated recommendations include giving conjugated pneumococcal vaccine to adult transplant candidates and recipients followed by the polysaccharide vaccine to increase serotype coverage. Human papillomavirus vaccine should also be given to transplant recipients, although the immunogenicity may be suboptimal. Quadrivalent meningococcal conjugate vaccine needs to be given in special circumstances such as to patients who are starting eculizumab therapy. Live vaccines in general are contraindicated, although increasing safety data are emerging for Varicella vaccine. Herpes Zoster vaccine may be offered prior to transplant, although the utility of this strategy regarding protection from shingles after transplant is not known. Newer vaccines such as inactivated zoster vaccine and vaccines for the prevention of cytomegalovirus are under study.

SUMMARY

Immunization for organ transplant recipients is an important part of pretransplant evaluation and the long-term care of the transplant recipient.

Outbreak of Influenza A(H1N1) in a Kidney Transplant Unit-Protective Effect of Vaccination

Seasonal influenza vaccination is recommended for patients with end-stage renal disease (ESRD), despite suggested inferior efficacy among these patients. We characterize an outbreak of influenza A(H1N1) in a kidney transplant unit. Altogether 23 patients were treated on the ward for postoperative care after kidney transplantation during the outbreak. After the first positive case, all patients were tested with nasopharyngeal swab tests and 7 patients were diagnosed with influenza A(H1N1). Altogether 17/23 patients had received adequate seasonal influenza vaccination, of whom 2/17 tested positive for influenza (one asymptomatic, one with mild cough). Five of six unvaccinated patients were diagnosed with influenza A(H1N1); 3/5 suffered from severe respiratory failure and were treated with ventilator support in the ICU, but all died due to acute respiratory distress syndrome, whereas 2/5 suffered from mild viral pneumonitis and recovered fully. The risk of influenza infection and mortality was significantly increased in unvaccinated patients (odds ratio 37.5 [95% CI 2.7-507.5, p = 0.01] and 6.7 [95% CI 2.3-18.9, p = 0.003], respectively). Influenza A(H1N1) had a high mortality in our cohort of nonvaccinated immunosuppressed patients early after kidney transplantation. None of the vaccinated patients developed serious disease, supporting the role of vaccination also for ESRD patients.

Immune efficacy of first and repeat trivalent influenza vaccine in healthy subjects and hemodialysis patients

Influenza vaccination is recommended to patients from groups at risk and to healthy persons alike. It is not completely clear whether persons vaccinated every year benefit more from the vaccination in any given season in comparison with those who are vaccinated for the first time. The aim of the study was to analyze whether influenza vaccination in previous seasons influences the response to ongoing vaccination in the healthy population and in hemodialyzed patients. The outcome measure was the production of anti-hemagglutinin antibodies in 71 hemodialyzed patients (Group A) and 63 patients of primary healthcare clinic, without chronic renal failure (Group B). The patients of these two groups were subdivided into never vaccinated before and previously vaccinated against influenza. After the current vaccination, significantly lower levels of anti-A/H1N1/ antibodies were found in the hemodialyzed compared with non-hemodialyzed previously vaccinated, but not unvaccinated, patients. The hemodialyzed patients, previously unvaccinated, had at baseline significantly lower levels of anti-A/H3N2/ and anti-B antibodies than those who were previously vaccinated; the differences were no longer significant after the current vaccination. We conclude that although antiflu immunization in previous seasons leads to higher baseline antibody titers in hemodialysis compromised patients, which is less evident in non-hemodialyzed patients, it is of little influence on the immunoresponse to current influenza vaccination, in both hemodialyzed and non-hemodialyzed patients.

Vaccination against infectious diseases: what is promising?

Vaccination has proven to be one of the best weapons protecting the mankind against infectious diseases. Along with the huge progress in microbiology, numerous highly efficacious and safe vaccines have been produced by conventional technology (cultivation), by the use of molecular biology (genetic modification), or by synthetic chemistry. Sterilising prevention is achieved by the stimulation of antibody production, while the stimulation of cell-mediated immune responses may prevent the outbreak of disease in consequence of an acute or reactivated infection. From several examples, two rules are deduced to evaluate the perspectives of future vaccine developments: They are promising, if (1) the natural infectious disease induces immunity or (2) passive immunisation (transfer of antibodies, adoptive transfer of lymphocytes) is successful in preventing infection.

Impact of immunosuppression on recall immune responses to influenza vaccination in stable renal transplant recipients

BACKGROUND

The recommendation by the American Society of Transplantation for annual trivalent inactivated influenza vaccination greater than 3 to 6 months post-kidney transplantation provides a unique opportunity to test the in vivo impact of immunosuppression on recall T- and B-cell responses to influenza vaccination.

METHODS

This study took advantage of recent breakthroughs in the single-cell quantification of human peripheral blood B-cell responses to prospectively evaluate both B- and T-cell responses to the seasonal (2010 and 2011) influenza vaccine in 23 stable renal transplant recipients and 22 healthy controls.

RESULTS AND CONCLUSION

The results demonstrate that the early B-cell response to influenza vaccination, quantified by the frequency of influenza-specific antibody-secreting cells (ASC) in peripheral blood, was significantly reduced in stable transplant recipients compared to healthy controls. The magnitude of the seroresponse and the rate of seroconversion were also blunted. The influenza-specific interferon-gamma (IFNγ) T-cell response was significantly reduced in transplant recipients; however, there was no correlation between the magnitude of the influenza-specific IgG ASC and IFNγ responses. The induction of memory T- and B-cell responses to influenza vaccination supports the recommendation to vaccinate while the blunted responses demonstrate the efficacy of immunosuppression in controlling memory responses individual transplant recipients.

Prevalence of antibodies against influenza A and B viruses in children in Germany, 2008 to 2010

The prevalence of influenza A and B virus-specific IgG was determined in sera taken between 2008 and 2010 from 1,665 children aged 0-17 years and 400 blood donors in Germany. ELISA on the basis of whole virus antigens was applied. Nearly all children aged nine years and older had antibodies against influenza A. In contrast, 40% of children aged 0-4 years did not have any influenza A virus-specific IgG antibodies. Eightysix percent of 0-6 year-olds, 47% of 7-12 year-olds and 20% of 13-17 year-olds were serologically naïve to influenza B viruses. By the age of 18 years, influenza B seroprevalence reached approximately 90%. There were obvious regional differences in the seroprevalence of influenza B in Germany. In conclusion, seroprevalences of influenza A and influenza B increase gradually during childhood. The majority of children older than eight years have basal immunity to influenza A, while comparable immunity against influenza B is only acquired at the age of 18 years. Children aged 0-6 years, showing an overall seroprevalence of 67% for influenza A and of 14% for influenza B, are especially at risk for primary infections during influenza B seasons.

Effectiveness of influenza vaccine in patients on hemodialysis--a review

The influenza virus is one of the most common causes of viral respiratory tract infections. Some chronic diseases predispose to a severe course of the disease and increase the risk of complications and death. To minimize the risk of infection and complications, care of patients with increased risk should include prophylactic measures such as the administration of a seasonal influenza vaccine. An influenza vaccine is the best and cheapest method of influenza prevention. It is indicated for patients with chronic kidney disease, both during conservative treatment and renal replacement therapy.

Many studies that have assessed the efficacy of an influenza vaccine in patients on hemodialysis have found that immune deficiency predisposes these patients to infection and a severe course of the disease. Because the immune response to a standard influenza vaccine in this population is weak, the studies covered many aspects of vaccination, including the need for a booster dose.

Unlike in a healthy population, the efficacy of an influenza vaccine in patients on hemodialysis might be insufficient; however, the vaccine is still able to induce immunity in a significant number of patients. Considering the latest data and the results of studies described above, the recommendation of a seasonal influenza vaccine should be obligatory in all hemodialysis patients.

This paper is based on original articles available from Medline database. The most recent and most significant literature on the influenza vaccine in patients on hemodialysis has been reviewed.

Differential influenza H1N1-specific humoral and cellular response kinetics in kidney transplant patients

Renal transplant recipients (RTR) are considered at high risk for influenza-associated complications due to immunosuppression. The efficacy of standard influenza vaccination in RTRs is unclear. Hence, we evaluated activation of the adaptive immunity by the pandemic influenza A(H1N1) 2009 (A(H1N1)pdm09) vaccine in RTRs as compared to healthy controls. To determine cross-reactivity and/or bystander activation, seasonal trivalent influenza vaccine and tetanus/diphteria toxoid (TT/DT) vaccine-specific T cells along with allospecific T cells were quantified before and after A(H1N1)pdm09 vaccination. Vaccination-induced alloimmunity was additionally determined by quantifying serum creatinine and proinflammatory protein IP-10. Contrary to healthy controls, RTRs required a booster vaccination to achieve seroconversion (13.3 % day 21; 90 % day 90). In contrast to humoral immunity, sufficient A(H1N1)pdm09-specific T-cell responses were mounted in RTRs already after the first immunization with a magnitude comparable with healthy controls. Interestingly, vaccination simultaneously boosted T cells reacting to seasonal flu but not to TT/DT, suggesting cross-activation. No alloimmune effects were recorded. In conclusion, protective antibody responses required booster vaccination. However, sufficient cellular immunity is established already after the first vaccination, demonstrating differential kinetics of humoral and cellular immunity.

Prevalence of antibodies to European porcine influenza viruses in humans living in high pig density areas of Germany

The risk of zoonotic human infection caused by European porcine influenza virus strains was estimated in German regions with a high pig density. Sera from 622 healthy volunteers were collected between April 2009 and November 2011, mainly in Westphalia and western Lower Saxony. These included 362 subjects with occupational contact to pigs and 260 blood donors without any direct exposition to pigs. Samples were analysed by the haemagglutination inhibition (HI) assay against a panel of six swine viruses of subtypes avian-like H1N1 and human-like H3N2 as well as against human H1N1 and H3N2 viruses including the pandemic H1N1 strain of 2009. Reciprocal HI titres ≥20 were quoted as seroreactive. Compared to the control group, a significantly higher proportion of subjects with direct contact to pigs exhibited seroreactivity against porcine antigens of the avian-like H1N1 (37.0 %/7.7 %), the human-like H3N2 (59.7 %/43.1 %), the pandemic H1N1 strain of 2009 (51.7 %/26.5 %) and against a historic seasonal H3N2 strain that is closely related antigenetically to currently circulating human-like H3N2 viruses of European pigs (57.5 %/36.5 %). This trend was also observed when a reciprocal HI titre ≥40 was chosen as cut-off. Particularly, in younger subjects, the differences in seroreactivity against porcine strains between the exposed and non-exposed group were significant. The data indicate a higher risk of infection in the exposed individuals.

"Trivalent influenza vaccination of healthy adults 3 years after the onset of swine-origin H1N1 pandemic: restricted immunogenicity of the new A/H1N1v constituent?"

Influenza vaccination is advised annually to reduce the burden of influenza disease. For sufficient vaccine campaigns also a continuous adoption of influenza vaccines are necessary, due to particularly high genetic variability of influenza A virus. Therefore, we evaluate the effectiveness of the trivalent influenza vaccine 2010/2011, against influenza A (H1N1, H3N2) and influenza B. Immune response was investigated in paired sera from 92 healthcare workers with the hemagglutination inhibition assay (HI). Protective antibody levels (HI titer ≥40) were found after vaccination for influenza A/California/07/2009(H1N1): 84.71 % [GMT: 115.34]; for influenza A/Perth/16/2009(H3N2): 94.94 % [GMT: 268.47] and for influenza B/Brisbane/60/2008: 96.20 % [GMT: 176.83]; matching with the currently circulating virus strains. However, the highest seroprevalence rate was found against influenza B; pre- and post-vaccination titers as well, which may be due to comparatively high virus preservation. Remarkable, lowest seropositivity was seen against H1N1. Despite the significant titer rise, sufficient H1N1 herd immunity was still not achieved. It can be assumed that a high influenza A herd immunity may be a requirement for a successful booster vaccination.