Host immune response to A(H1N1)pdm09 vaccination and infection: a one-year prospective study on six cohorts of subjects

Background

The long-term immunogenicity after novel vaccine against A(H1N1)pdm09 administration or natural infection has not been well investigated.

Methods

Six cohorts of subjects were followed up for over one year: one-dose A(H1N1)pdm09 vaccine recipient, A(H1N1)pdm09-seasonal trivalent vaccine recipients in different orders, confirmed A(H1N1)pdm09 patients without vaccination, with previous A(H1N1)pdm09 or seasonal influenza vaccination. Peripheral blood mononuclear cells and sera samples were collected at baseline and month 1, 2, 3, 7 and 14 after vaccination (infection). The immunogenicity was determined by hemagglutination-inhibition (HI) and B cell enzyme-linked immunospot (ELISPOT) assays.

Results

Single dose of A(H1N1)pdm09 vaccine elicited antibody titer of greater than 1:40 in 40% adults for 1 year and mean live of this adequate antibody was determined as 8.35 months. In contrast, responses after natural infections had lower peaking level and a relatively longer antibody duration, with estimated mean lives of 11.8 months. Pre-vaccination with the seasonal flu vaccine led to a significant reduction in HI titer to A(H1N1)pdm09 one month after vaccination, while pre-vaccination with A(H1N1)pdm09 had no effect on seasonal influenza vaccination. Seasonal flu vaccination followed by A(H1N1)pdm09 infection elicited boosting effect on antibody response against A(H1N1)pdm09. A similar memory B cell response was elicited from both vaccination and infection by ELISPOT assay.

Conclusions

The long-term decay of immunity for A(H1N1)pdm09 vaccine and natural infection indicates the need of revaccination after the host lose protection acquired from either vaccination or infection. Prior infection, rather than the pre-vaccination with seasonal influenza could act on the host immunity to elicit boosting effect on the A(H1N1)pdm09.     

Influenza vaccine effectiveness against medically-attended influenza illness during the 2012–2013 season in Beijing,China

Background

Influenza vaccine coverage remains low in China, and there is limited information on the preventive value of local vaccination programs.

Methods

As part of influenza virological surveillance in Beijing, China during the 2012–2013 influenza season, we assessed the vaccine effectiveness (VE) of one or more doses of trivalent inactivated influenza vaccine (IIV3) in preventing medically-attended influenza-like-illness (ILI) associated with laboratory-confirmed influenza virus infection using a test-negative case–control design. Influenza vaccination was determined based on self-report by adult patients or the parents of child patients.

Results

Of 1998 patients with ILI, 695 (35%) tested positive for influenza viruses, including 292 (42%) A(H3N2), 398 (57%) A(H1N1)pdm09, and 5 (1%) not (sub)typed influenza viruses. The rate of influenza vaccination among all patients was 4% (71/1998). Among influenza positive patients, 2% (57/1303) were vaccinated compared to 4% (14/695) among influenza negative patients, resulting in VE for one or more doses of vaccine (adjusted for age, sex, week, and days since illness onset) against all circulating influenza viruses of 52% (95% CI = 12–74%). A significant adjusted VE for one or more doses of vaccine for all ages against A(H1N1)pdm09 of 59% (95% CI, 8–82%) was observed; however, the VE against A(H3N2) was 43% (95% CI, −30% to 75%). The point estimate of VE was 59% (95% CI, 19–79%) for those aged <60 years, but a negative VE point estimate without statistical significance was observed among those aged ≥60 years.

Conclusions

IIV3 conferred moderate protection against medically-attended influenza in Beijing, China during the 2012–2013 season, especially against the A(H1N1)pdm09 strain and among those aged <60 years old.     

Pandemic influenza A(H1N1)pdm09 improves vaccination routine in subsequent years: A cohort study from 2009 to 2011

Background

In 2009 the pandemic influenza virus A(H1N1)pdm09 emerged with guidance that people at risk should be vaccinated. It is unclear how this event affected the underlying seasonal vaccination rate in subsequent years.

Purpose

To investigate the association of pandemic influenza A(H1N1)pdm09 and seasonal flu vaccination status in 2009 with vaccination rates in 2010 and 2011.

Methods

Data were collected in 40 Dutch family practices on patients at risk for influenza during 2009–2011; data analysis was conducted in 2012.

Results

A multilevel logistic regression model (n = 41,843 patients) adjusted for practice and patient characteristics (age and gender, as well as those patient groups at risk), showed that people who were vaccinated against A(H1N1)pdm09 in 2009 were more likely to have been vaccinated in 2010 (OR 6.02; 95%CI 5.62–6.45, p < .0001). This likelihood was even more for people who were vaccinated against seasonal flu in 2009 (OR 13.83; 95%CI 12.93–14.78, p < .0001). A second analysis on the uptake rate in 2011 (n = 39,468 patients) showed that the influence of the vaccination state in 2009 declined after two years, but the diminishing effect was smaller for people vaccinated against A(H1N1)pdm09 than for seasonal flu (OR 5.50; 95%CI 5.13–5.90, p < .0001; OR 10.98; 95%CI 10.26–11.75, p < .0001, respectively).

Conclusion

Being vaccinated against A(H1N1)pdm09 and seasonal influenza in the pandemic year 2009 enhanced the probability of vaccination in the next year and this was still effective in 2011. This suggests that peoples’ vaccination routines were not changed by the rumor around the outbreak of A(H1N1)pdm09, but rather confirmed underlying behavior.     

The effectiveness of influenza vaccination in preventing hospitalizations in children in Hong Kong, 2009–2013

Background

Influenza vaccination is widely recommended every year to protect individuals against influenza virus infection and illness. There are few published estimates of influenza vaccine effectiveness against hospitalization in children or from subtropical regions.

Methods

We conducted a test-negative year-round study between October 2009 and September 2013, recruiting children 6 months to 17 years of age admitted to two hospitals in Hong Kong with a febrile acute respiratory infection. Cases were tested for influenza A and B and conditional logistic regression was used to estimate vaccine effectiveness comparing influenza vaccination history of the trivalent influenza vaccine (TIV) among patients testing positive versus negative for influenza, adjusting for age and sex and matching by calendar week of recruitment.

Results

Overall vaccine effectiveness against hospitalization with laboratory-confirmed influenza A and B was estimated to be 61.7% (95% CI: 43.0%, 74.2%). The estimated vaccine effectiveness against A(H3N2) was 36.6% (95% CI: −25.5%, 67.9%) compared to 71.5% (95% CI: 39.4%, 86.6%) for A(H1N1)pdm09 and 68.8% (95% CI: 41.6%, 83.3%) for B.

Conclusions

Vaccine effectiveness against hospitalization in children varied from year to year, but was moderate to high overall even in an area with influenza activity throughout the year.     

The impact of pandemic A(H1N1)pdm09 influenza and vaccine-associated adverse events on parental attitudes and influenza vaccine uptake in young children

Introduction

Parental attitudes towards vaccination significantly influence vaccine uptake. The A(H1N1)pdm09 influenza pandemic was followed in 2010 by an unprecedented increase in febrile reactions in children receiving trivalent inactivated influenza vaccine manufactured by bioCSL. Uptake of TIV in children <5 years in Western Australia (WA) decreased in 2010 and has remained low. The impact of pandemic A(H1N1)pdm09 and adverse-events on parental attitudes towards vaccination is uncertain.

Materials and Methods

A parental attitudes survey towards influenza illness and vaccination was conducted as part of the West Australian Influenza Vaccine Effectiveness study. Vaccination status was assessed by parental interview and confirmed by the national register and/or vaccine providers. Parental attitudes from vaccinated and unvaccinated children and attitudes in 2008–2009 and 2010–2012 were compared. Principal Component Analysis was conducted to determine core attitudes that influenced vaccine uptake.

Results

Vaccination history and parental attitude surveys were available from 2576 children. Parents of fully vaccinated children less frequently stated that influenza was a mild disease, more frequently stated that influenza vaccine was safe and were less frequently worried about vaccine side effects.Uptake of influenza vaccine decreased significantly from 2010 onwards. From 2010, parents were less concerned about severe influenza, but more concerned about vaccine side effects and safety. Despite this significant shift in attitudes towards influenza vaccine, parental acceptance of vaccines on the national immunisation program did not change. Principal Component Analysis revealed that attitudes around vaccine safety and efficacy were the most important attitudes impacting on vaccine uptake.

Conclusions

Parental attitudes to influenza vaccine changed from 2010. Confidence in the WA preschool influenza vaccination program remains low yet appeared unchanged for other vaccines. Restoring public confidence in childhood influenza vaccination is needed before uptake can be improved.     

External cues to action and influenza vaccination among post-graduate trainee physicians in Toronto,Canada

Background

Understanding factors affecting trainee physician choices about vaccination may permit the design of more effective vaccination programmes.

Methods

To identify factors associated with seasonal and pandemic influenza vaccination, an online questionnaire based on the health belief model was sent to trainee physicians registered at the post-graduate medical education office at the University of Toronto in September 2011.

Results

963 complete responses were received from 1884 trainee physicians (51%); 28 (2.9%) reported an allergy to vaccine components and were excluded from further analysis. Reported seasonal influenza vaccination rates in 2008, 2009 and 2010 were 69% (648/935), 75% (708/935) and 76% (703/935), respectively; 788 (84%) reported receiving the A(H1N1)pdm09 vaccine. In multivariable analysis, number of years of post-graduate training (OR for 4+ versus 1–3 post-graduate years 2.2 (95% CL 1.3, 3.8)) was associated with receipt of the 2009 pandemic vaccine, as were four components of the health belief model: odds ratios were 4.7 (95% CL 3.0, 7.5) for perceived severity, 1.9 (95% CL 1.2, 2.9) for perceived benefits, .35 (95% CL .21, .59) for perceived barriers, and 5.8 (95% CLI 3.6, 9.1) for external cues to action. Both vaccinated and unvaccinated respondents reported that their decisions were significantly influenced by encouragement from their colleagues, families and employers.

Conclusion

Self-reported vaccination coverage among trainee physicians was high. External cues to action appear to be particularly important in trainee physician vaccination decisions: active institutional promotion may increase influenza vaccination rates in trainees.     

Pre-vaccination immunity and immune responses to a cell culture-derived whole-virus H1N1 vaccine are similar to a seasonal influenza vaccine

Background

Immune responses to novel pandemic influenza vaccines may be influenced by previous exposure to antigenically similar seasonal strains.

Methods

An open-label, randomized, phase I/II study was conducted to assess the immunogenicity and safety of a non-adjuvanted, inactivated whole-virus H1N1 A/California/07/2009 vaccine. 408 subjects were stratified by age (18–59 and >60 years) and randomized 1:1 to receive two vaccinations with either 3.75 or 7.5 μg hemagglutinin antigen 21 days apart. Safety, immunogenicity and the influence of seasonal influenza vaccination and antibody cross-reactivity with a seasonal H1N1 strain was assessed.

Results

A single vaccination with either dose induced substantial increases in H1N1 A/California/07/2009 hemagglutination inhibition (HI) and neutralizing (MN) antibody titers in both adult and elderly subjects. A single 7.5 μg dose induced seroprotection rates of 86.9% in adults and 75.2% in elderly subjects. Two 7.5 μg vaccinations induced seroprotection rates in adult and elderly subjects of 90.9% and 89.1%, respectively. The robust immune response to vaccination was confirmed by analyses of neutralizing antibody titers. Both HI and MN antibodies persisted for ≥6 months post-vaccination. Between 34% and 49% of subjects had seroprotective levels of H1N1 A/California/07/2009 antibodies at baseline. Higher baseline HI titers were associated with receipt of the 2008–09 or 2009–10 seasonal influenza vaccine. High baseline A/California/07/2009 neutralizing antibody titers were also associated with high baseline titers against A/New Caledonia/20/99, a seasonal H1N1 strain which circulated and was included in the seasonal vaccine from 2000–01 to 2006–07. Pre-adsorption with A/H1N1/New Caledonia/20/99 antigen reduced A/H1N1/California/07/2009 baseline titers in 55% of tested sera. The vaccine was well tolerated with low rates of fever.

Conclusions

A whole-virus H1N1 A/California/07/2009 vaccine was safe and well tolerated and a single dose induced substantial immune responses similar to seasonal influenza vaccines, probably due to immunological priming by previous seasonal influenza vaccines or infections.     

Comparable humoral response after two doses of adjuvanted influenza A/H1N1pdm2009 vaccine or natural infection in allogeneic stem cell transplant recipients

Background

The present study evaluated immunogenicity and tolerance of two-dose influenza A/H1N1pdm09 vaccination in allogeneic hematopoietic stem cell transplantation (HSCT) recipients, and compared the vaccine-induced humoral response to that triggered by natural infection in another group of HSCT patients.

Methods

Adult allogeneic HSCT recipients vaccinated with two doses of influenza A/H1N1pdm09 vaccine, separated by 3 weeks, and patients with proven influenza A/H1N1pdm09 infection were included. Antibody responses were measured by hemagglutination-inhibition assay 1) on days 0, 21, 42 and 6 months after the first vaccine injection in vaccinated patients and 2) before pandemic and after influenza A/H1N1pdm09 infection, in patients presented natural infection.

Results

At baseline, 3% of 59 recipients of adjuvanted vaccine and 0% of 20 infected patients were seroprotected (antibody titer ≥ 1/40). Seroprotection rate observed 42 days after vaccination was not different from that observed after natural infection (66% and 60% respectively, p = 0.78). In vaccinated patients, seroprotection rate increased significantly from 54% to 66% between day 21 and 42 (p = 0.015). Moreover, after 6 months, seroprotection rate in 21 vaccinated patients was similar to that observed in 10 infected patients evaluated at least 76 days after infection (D76–217) (60% and 81% respectively, p = 0.2). In multivariate analysis, no immunosuppressive treatment or chronic graft-versus-host disease (GVHD) and longer time between transplantation and vaccination/infection were associated with a stronger humoral response. The adjuvanted vaccine was safe with low rate of GVHD worsening.

Conclusion

In HSCT recipients, two doses of influenza A/H1N1pdm09 adjuvanted vaccine were safe and induced a humoral response comparable to that triggered by natural infection in these patients.     

Increased risk of anaphylaxis following administration of 2009 AS03-adjuvanted monovalent pandemic A/H1N1 (H1N1pdm09) vaccine

Background

Anaphylaxis after trivalent influenza vaccination is typically reported at a rate of <1 per million doses. In Quebec, Canada, anaphylaxis following administration of the monovalent AS03-adjuvanted H1N1pdm09 vaccine was reported through passive surveillance at a rate of 8 per million doses administered. This was 20 times higher than the reporting rate for non-adjuvanted trivalent vaccines administered during the six previous seasons. However, adequate estimation of the incidence of anaphylaxis is hindered by wide variations in definitions and diagnosis.

Methods

Using the Brighton collaboration case definition of anaphylaxis, all cases with allergic symptoms (AS) reported to public health were reviewed to estimate the incidence of anaphylaxis following AS03-adjuvanted H1N1pdm09 vaccine.

Results

Among 752 reports of allergic symptoms, 33 were initially reported as anaphylaxis of which 20/33 (60%) met the Brighton definition (19/20 with certainty levels 1 or 2). A total of 38 additional cases with onset within 1 h of vaccination also met the Brighton definition of anaphylaxis (27 (71%) with certainty levels 1 or 2). The 58 cases meeting Brighton Level 1 or 2 criteria for anaphylaxis represent a 75% increase over the 33 passively reported and an incidence of 13 per million doses administered.

Conclusion

A substantial number of patients with early-onset allergic symptoms met the most specific levels of the Brighton case definition but were not reported as anaphylaxis. Based on this specific case definition, the incidence of anaphylaxis after AS03-adjuvanted H1N1pdm09 vaccine substantially exceeded that reported with seasonal influenza vaccines, a signal that warrants better understanding.     

No association between influenza A(H1N1)pdm09 vaccination and narcolepsy in South Korea: An ecological study

Background

There is concern about a possible association between influenza A(H1N1)pdm09 vaccination and narcolepsy. In this study, we assessed the incidence and incidence rate of narcolepsy in the South Korean population before and after the implementation of an A(H1N1)pdm09 vaccination campaign to see if vaccination led to a change in the occurrence of narcolepsy.

Methods

We conducted an ecological study, comparing incident cases and incidence rates for newly diagnosed narcolepsy case-patients in South Korea, between July 2006 and June 2011. We used data from the Health Insurance Review Agency and Korea Centers for Disease Control and Prevention, which have limited information on case ascertainment. During vaccination campaign period, South Korea used non-adjuvanted and MF59-adjuvanted A(H1N1)pdm09 vaccines.

Results

Generally, incidence rate was highest in prepandemic period. No trend toward increase in the incidence of narcolepsy after pandemic period was found. Observation of incidence by season did not suggest any time pattern for occurrence of narcolepsy.

Conclusion

No increase in cases or incidence rate for narcolepsy during the A(H1N1)pdm09 vaccination campaign was found in South Korea. Our data do not support the use of MF59-adjuvanted or non-adjuvanted A(H1N1)pdm09 vaccine as a trigger for narcolepsy on a population level.     

Barriers to influenza vaccination among pregnant women

Objective

Despite pregnant women's increased morbidity and mortality from influenza, vaccination rates remain low. This study intended to evaluate barriers to pregnant women's uptake of influenza vaccine.

Study design

A survey was designed that assessed participant demographics, knowledge, beliefs, attitudes, and general experiences with seasonal and 2009 novel H1N1 influenza. Associations between patient characteristics and vaccine uptake were then assessed.

Results

88 women completed the survey. Women who correctly answered >75% of knowledge questions regarding influenza were significantly more likely to accept the influenza vaccine (seasonal: p = 0.04, H1N1: p < 0.01). Conversely, patients who declined the vaccine were more likely to hold false beliefs, such as perceiving that the vaccine was not protective (seasonal: p < 0.01, H1N1: p < .01) and that they were not at risk for influenza (seasonal: p <  0.01).

Conclusion

The reasons for influenza vaccine declination in pregnant patients include lower levels of knowledge and unfavorable attitudes regarding the safety and efficacy of the vaccine, and suggest the importance of education as a tool to improve vaccination uptake     

General practice encounters following seasonal influenza vaccination as a proxy measure of early-onset adverse events

Background

In 2010, use of seasonal trivalent influenza vaccine (TIV) in children <5 years of age was suspended in Australia following reports of vaccine-related febrile convulsions. We investigated the utility of data on primary care [general practice (GP)] consultations for any reason within three days of receipt of influenza vaccine as recorded on the Australian Childhood Immunisation Register (ACIR) as a means of signal detection.

Methods

Data on GP consultations were obtained from Medicare Australia (Australian Government Department of Human Services) for children recorded on the ACIR as receiving either TIV or monovalent influenza vaccine. Rates of GP consultation by day following ACIR-recorded receipt of influenza vaccine were compared by year (2008–2010), vaccine type, age and region.

Results

In 2010, GP encounter rates on the day after receipt of the TIV manufactured by bioCSL (formerly CSL Biotherapies (Fluvax^®) were significantly higher than both bioCSL TIVs in the previous two years [rate ratio (RR) 1.9; 95% CI: 1.7–2.2] and Sanofi Pasteur TIV, Vaxigrip^® [RR 1.6, 95% CI 1.4–1.7] in 2009–2010. Encounter rates were also higher than for CSL Monovalent influenza vaccine, Panvax^® [RR 1.9, 95% CI 1.7–2.2] in 2009–2010. These findings were robust to adjustment for age group (≤2, >2 years) and region (Western Australia vs other Australian states/territories).

Conclusions

A primary care consultation on the day after vaccine receipt is a reasonable proxy for early reactogenicity and has potential for use in various settings.     

Inactivated trivalent seasonal influenza vaccine induces limited cross-reactive neutralizing antibody responses against 2009 pandemic and 1934 PR8 H1N1 strains

Background

In June 2009, we conducted a prospective study in Singapore on 51 individuals to determine their serologic responses before and following receipt of the 2009 Southern Hemisphere seasonal influenza vaccine.

Materials and methods

Paired serum samples were obtained before and 3–4 weeks after vaccination. Virus microneutralization assays were performed to quantify antibodies against A/Brisbane/59/2007 vaccine, pandemic H1N1-2009 and A/Puerto Rico/08/34 H1N1 strains.

Results

Post-vaccination, 43%, 12% and 24% of subjects displayed a 4-fold or greater rise in neutralizing antibody titers against the three strains, respectively. There was a positive correlation among individuals who showed increased titers to both pandemic H1N1-2009 and A/Puerto Rico/08/34 (p < 0.001). However, this correlation was not observed for A/Brisbane/59/2007 with either strain. The relative conservation and accessibility of predicted B-cell epitopes may explain the limited cross-reactivity of the antibodies directed against common H1N1 epitopes.

Conclusions

These results suggest that seasonal influenza vaccination confers a certain degree of cross-protection to other H1N1 strains. The correlation in cross-reactive antibody titers to A/Puerto Rico/08/34 and pandemic H1N1-2009 implies that previous exposure to pre-1957 H1N1 strains may confer some protection against the 2009 pandemic strain.     

Monovalent H1N1 influenza vaccine safety in pregnant women,risks for acute adverse events

Objective

To assess risks for acute adverse events and pregnancy complications in pregnant women following monovalent 2009 H1N1 inactivated influenza (MIV) vaccination.

Methods

Within the Vaccine Safety Datalink, we compared rates of pre-specified medically attended events (MAE) occurring within 42 days of MIV vaccination to those occurring in matched cohorts that at the same gestational age were either unvaccinated or received seasonal trivalent inactivated influenza (TIV) vaccine. Using generalized estimating equation method, with a Poisson distribution and log link, we calculated adjusted incident rate ratios (AIRR).

Results

Among 9349 women receiving MIV in any trimester, only one MAE occurred 0–3 days following MIV, an allergic reaction. No cases of Guillain–Barré syndrome, Bell's palsy, or transverse myelitis occurred 1–42 days after MIV. Compared to women receiving TIV and to unvaccinated women, risks for acute MAEs were not increased following MIV for any outcome. Hyperemesis was the most common adverse event in the MIV, TIV, and unvaccinated groups, occurring at a rate of about 4% over a 42-day period in all groups. Over a 42-day window, among all groups, incident gestational diabetes occurred at a rate of 3% and thrombocytopenia occurred at a rate of approximately 0.3%. Among women receiving MIV during pregnancy, increased risks for these and other less common obstetric events were not detected.

Conclusion

In this large cohort of pregnant women no acute safety signals were identified within 6 weeks of receipt of MIV.     

Clinical development of a Vero cell culture-derived seasonal influenza vaccine

Background

Cell culture technologies have the potential to improve the robustness and flexibility of influenza vaccine supply and to substantially shorten manufacturing timelines. We investigated the safety, immunogenicity and efficacy of a Vero cell culture-derived seasonal influenza vaccine and utilized these studies to establish a serological correlate of vaccine protection.

Methods

Two multicenter, randomized, double-blind phase III trials were undertaken in the US during the 2008–2009 Northern hemisphere influenza season, in young (18–49 years) and older (50–64 years and ≥65 years) adult subjects. 7250 young adults were randomized 1:1 to receive either Vero-derived vaccine or placebo. 3210 older adult subjects were randomized 8:1 to receive either Vero-derived vaccine or a licensed egg-derived vaccine. Serum hemagglutination inhibition antibody titers were assessed 21 days post-vaccination. Vaccine efficacy in preventing cell culture-confirmed influenza infection was determined for the young adult population. Local and systemic adverse events were recorded in both studies.

Results

The Vero-derived vaccine was safe and well tolerated in both young and older adults. All US and European immunological licensing thresholds were comfortably met in both populations. Vaccine efficacy in young adults was 79% against A/H1N1 viruses antigenically matching the corresponding vaccine strain and 78.5% for all antigenically matched influenza viruses. A hemagglutination inhibition antibody titer of ≥1:15 provided a reliable correlate of protection for the Vero-derived influenza vaccine, with no additional benefit at titers >1:30. Bridging of the correlate of protection established in the young adult population to the older adult immunogenicity data demonstrated the likely effectiveness of the Vero-derived vaccine in the older adult population.

Conclusions

A Vero cell culture-derived seasonal influenza vaccine is safe, immunogenic and protects against infection with influenza virus. The novel vaccine technology has the potential to make a substantial contribution to improving influenza vaccine supply.

Clinical trial registration

The studies are registered with ClinicalTrials.gov, numbers NCT00566345 and NCT00782431.     

Evaluating the safety of influenza vaccine using a claims-based health system

Introduction

As part of the Centers for Disease Control and Prevention's monitoring and evaluation activities for influenza vaccines, we examined relationships between influenza vaccination and selected outcomes in the 2009–2010 and 2010–2011 influenza seasons in a claims-based data environment.

Methods

We included patients with claims for trivalent influenza vaccine (TIV) and/or 2009 pandemic influenza A H1N1 vaccine (H1N1) during the 2009–2010 and 2010–2011 influenza seasons. Patients were followed for several pre-specified outcomes identified in claims. Seizures and Guillain–Barré Syndrome were selected a priori for medical record confirmation. We estimated incidence rate ratios (IRR) using a self-controlled risk interval (SCRI) or a historical comparison design. Outcomes with elevated IRRs, not selected a priori for medical record review, were further investigated with review of claims histories surrounding the outcome date to determine whether the potential event could be ruled-out or attributed to other causes based on the pattern of medical care.

Results

In the 2009–2010 season, no significant increased risks for outcomes following H1N1 vaccination were observed. Following TIV administration, the IRR for peripheral nervous system disorders and neuropathy was slightly elevated (1.07, 95% CI: 1.01–1.13). The IRR for anaphylaxis following TIV was 28.55 (95% CI: 3.57–228.44). After further investigation of claims histories, the majority of potential anaphylaxis cases had additional claims around the time of the event indicating alternate explanatory factors or diagnoses. In the 2010–2011 season following TIV administration, a non-significant elevated IRR for anaphylaxis was observed with no other significant outcome findings.

Conclusion

After claims history review, we ultimately found no increased outcome risk following administration of 998,881 TIV and 538,257 H1N1 vaccine doses in the 2009–2010 season, and 1,158,932 TIV doses in the 2010–2011 season.     

Predictors of IV behaviors during and after the 2009 influenza pandemic in France

Background

Controversies about the 2009 H1N1 pandemic influenza vaccination might have impacted the motivational processes that underlie individual immunization against seasonal influenza. The purpose of this article is to investigate correlates of vaccine uptake during and after the pandemic.

Methods

Data from the 1174 subjects of the CoPanFlu France cohort aged 15 and over were used. We used logistic regression models to identify social and behavioral predictors of getting vaccinated against seasonal influenza in 2009–2010 and in 2010–2011 and against H1N1 influenza in 2009–2010.

Results

This study points out that correlates of vaccination behaviors varied according to the vaccine. Respondents under 65 years who adopted the seasonal influenza vaccine were, as usual, more likely to belong to a target group and have a lower education, contrary to subjects who chose the pandemic vaccine. Exceptionally during the pandemic, a higher socioeconomic status also led to adoption of either vaccine. Motivational processes differed by vaccine. Uptaking the “new” pandemic vaccine was the result of a deliberative decision-making process, influenced by cognitive factors related to the pandemic context (such as perceived severity of the H1N1 flu strain and trust in public health authorities). In contrast, respondents got the seasonal flu vaccine without relying on explicit justifications, but instead through habit of performing this behavior in the past.

Conclusions

Target groups for seasonal influenza but not those for pandemic influenza were more likely to adopt the pandemic vaccine, which is a cause for great concern. This may be due to large extent to the automatic and habitual nature of influenza vaccination decisions. Public health authorities, should pay more attention to situational than informational cues to facilitate vaccine uptake among priority groups, especially in case of mild pandemic influenza.     

The determinants of 2009 pandemic A/H1N1 influenza vaccination: a systematic review

Background

Pandemic A/H1N1 influenza vaccine coverage varied widely across countries. To understand the factors influencing pandemic influenza vaccination and to guide the development of successful vaccination programs for future influenza pandemics, we identified and summarized studies examining the determinants of vaccination during the 2009 influenza pandemic.

Methods

We performed a systematic literature review using the PubMED electronic database from June 2009 to February 2011. We included studies examining an association between a possible predictive variable and actual receipt of the pandemic A/H1N1 influenza vaccine. We excluded studies examining intention or willingness to receive the vaccine.

Results

Twenty-seven studies were identified from twelve countries. Pandemic influenza vaccine coverage varied from 4.8% to 92%. Coverage varied by population sub-group, country, and assessment method used. Most studies used questionnaires to estimate vaccine coverage, however seven (26%) used a vaccination registry. Factors that positively influenced pandemic influenza vaccination were: male sex, younger age, higher education, being a doctor, being in a priority group for which vaccination was recommended, receiving a prior seasonal influenza vaccination, believing the vaccine to be safe and/or effective, and obtaining information from official medical sources.

Conclusions

Vaccine coverage during the pandemic varied widely across countries and population sub-groups. We identified some consistent determinants of this variation that can be targeted to increase vaccination during future influenza pandemics.