Factors influencing pandemic influenza vaccination of healthcare workers--a systematic review

Introduction

Maintaining the health and availability of Health care workers (HCW) is an essential component of pandemic preparedness. A key to protecting HCW during the H1N1 pandemic was influenza vaccination. Numerous researchers have reported on factors influencing H1N1 vaccination behaviour in various HCW groups. This systematic review aims to inform future influenza vaccine interventions and pandemic planning processes via the examination of literature in HCW H1N1 vaccination, in order to identify factors that are (1) unique to pandemic influenza vaccination and (2) similar to seasonal influenza vaccination research.

Methods

We conducted a comprehensive review of literature (MEDLINE, PubMed, EMBASE, PsycINFO, CINHAL, AMED, Cochrane Library, ProQuest, and grey literature sources) published between January 2005 and December 2011 to identify studies relevant to HCW pH1N1 vaccine uptake/refusal.

Results

20 publications sampling HCW from different geographic regions are included in this review. H1N1 vaccine coverage was found to be variable (9–92%) across HCW populations, and self-reported vaccine status was the most frequently utilized predictor of pandemic vaccination. HCW were likely to accept the H1N1 vaccine if they perceived, (1) the H1N1 vaccine to be safe, (2) H1N1 vaccination to be effective in preventing infection to self and others (i.e. loved ones, co-workers and patients), and (3) H1N1 was a serious and severe infection. Positive cues to action, such as the access of scientific literature, trust in public health communications and messaging, and encouragement from loved ones, physicians and co-workers were also found to influence HCW H1N1 uptake. Previous seasonal influenza vaccination was found to be an important socio-demographic predictor of vaccine uptake. Factors unique to HCW pandemic vaccine behaviour are (1) lack of time and vaccine access related barriers to vaccination, (2) perceptions of novel and rapid pandemic vaccine formulation, and (3) the strong role of mass media on vaccine uptake.

Conclusions

Many of the factors that influenced HCW pandemic vaccination decisions have previously been reported in seasonal influenza vaccination literature, but some factors were unique to pandemic vaccination. Future influenza vaccine campaigns should emphasize the benefits of vaccination and highlight positive cues to vaccination, while addressing barriers to vaccine uptake in order to improve vaccine coverage among HCW populations. Since pandemic vaccination factors tend be similar among different HCW groups, successful pandemic vaccination strategies may be effective across numerous HCW populations in pandemic scenarios.     

Factors associated with uptake of seasonal and pandemic influenza vaccine among clinical risk groups in the UK: an analysis using the General Practice Research Database

Background

Influenza vaccine uptake rates are low compared with uptake rates of many other vaccines. It is unclear how this differs between risk groups in the population and between pandemic and non-pandemic influenza vaccines.

Aim

This study sought to estimate uptake rates of pandemic and seasonal influenza vaccines among clinical risk groups in the UK during the 2009/2010 influenza season and to identify predictors of vaccine uptake in this cohort.

Methods

Uptake rates were calculated using data from the UK General Practice Research Database (GPRD). Predictors of vaccination were identified using a modified Poisson regression with robust standard error estimates.

Results

Uptake of pandemic influenza vaccine in clinical risk groups was 40.3% and uptake of seasonal influenza vaccine was 61.3%. Factors found to be predictive of seasonal and pandemic influenza vaccination included age and the total number of underlying health conditions an individual had. At risk individuals in those age groups in which universal vaccination of the general population was recommended were more likely to have been vaccinated than individuals in age groups in which only clinical risk groups were recommended for vaccination; hence children in clinical risk groups were more likely to receive pandemic than seasonal influenza vaccine. In older people, having a history of Guillain Barré syndrome was associated with a reduced likelihood of receipt of both seasonal (IRR_adj 0.83, CI₉₅ 0.77–0.90) and pandemic influenza vaccines (IRR_adj 0.82, CI₉₅ 0.73–0.92).

Discussion

Uptake of pandemic influenza vaccine was lower than that of seasonal influenza vaccine among those at a clinically high risk of influenza related morbidity. This suggests that vaccination strategies may need to be altered during future pandemics. Recommending universal vaccination within age categories in which there is a large proportion of high risk individuals could be considered as this may result in higher uptake among clinical risk groups.     

Acceptability of pandemic A(H1N1) influenza vaccination by Essential Community Workers in 2010 Alicante (Spain), perceived seriousness and sources of information

Objective

Describe acceptability of pandemic A(H1N1) influenza vaccination by Essential Community Workers (ECWs) from Alicante province (Spain) in January 2010. Evaluate the correlation with attitudes, beliefs, professional advice and information broadcasted by media.

Method

In this cross-sectional study, face-to-face interviews were conducted with 742 ECWs to assess their attitudes towards vaccination against the pandemic influenza strain. A multivariable regression model was made to adjust the Odds Ratios (ORs).

Results

Some ECWs reported having been vaccinated with seasonal vaccine, 21.5% (95%IC 18.6–24.9); only 15.4% (95%IC 12.8–18.4) with the pandemic one. ECWs vaccinated regularly against seasonal flu (OR 5.1; 95%IC 2.9–9.1), those who considered pandemic influenza as a severe or more serious disease than seasonal flu (OR 3.8; 95%IC 2.1–6.7) and those who never had doubts about vaccine safety (OR 3.7; 95%IC2.1–6.7) had a better acceptance of pandemic vaccine. Finally, 78.7% (95%IC 75.1–81.4) had doubts about pandemic vaccine's effectiveness.

Conclusion

The vast amount of information provided by the media did not seem to be decisive to prevent doubts or to improve the acceptability of the vaccine in ECWs. Professional advice should be the focus of interest in future influenza vaccination campaigns. These results should be taken into account by health authorities.     

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.     

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.     

Determinants of uptake of influenza vaccination among pregnant women – A systematic review

Background

Pregnant women have the highest priority for seasonal influenza vaccine. However, suboptimal coverage has been repeatedly noted in this population. To improve vaccine uptake, reviewing the determinants of vaccination is of increasing importance.

Methods

A detailed literature search was performed up to November 30, 2013 to retrieve articles related to uptake of influenza vaccination during pregnancy.

Results

Forty-five research papers were included in the review. Twenty-one studies assessed the coverage of seasonal influenza vaccination, 13 studies assessed coverage of A/H1N1 pandemic vaccination and 11 studies assessed both. Vaccination uptake ranged from 1.7% to 88.4% for seasonal influenza, and from 6.2% to 85.7% for A/H1N1 pandemic influenza. Many pregnant women were unaware that they were at high risk for influenza and its complications during pregnancy. They were also more likely to underestimate the threat of influenza to themselves and their fetus. Moreover, they had substantial concerns about the safety and efficacy of the influenza vaccine during pregnancy. Negative media reports contributed to the perception that influenza vaccination during pregnancy was risky and could result in adverse pregnancy outcomes. Although health care providers’ (HCPs) recommendations were consistently associated with vaccine uptake, most did not recommend the vaccine to their pregnant clients.

Conclusions

Influenza vaccination uptake among pregnant women is suboptimal and HCPs rarely recommend it. Positive vaccination recommendations from HCPs as well as direct access to the vaccine would likely substantially improve vaccination acceptance.     

Theory-based predictors of influenza vaccination among pregnant women

Background

Guidelines recommend influenza vaccination for pregnant women, but vaccine uptake in this population is far below the goal set by Healthy People 2020. The purpose of this study was to examine predictors of seasonal influenza vaccination among pregnant women.

Methods

Between 2009 and 2012, the Vaccines and Medications in Pregnancy Surveillance System (VAMPSS) conducted a prospective cohort study of influenza vaccine safety among pregnant women in the US and Canada that oversampled vaccinated women. Data for the present paper are from an additional cross-sectional telephone survey completed during the 2010–2011 influenza season. We examined predictors of influenza vaccination, focusing on Health Belief Model (HBM) constructs.

Results

We surveyed 199 pregnant women, 81% of whom had received a seasonal influenza vaccine. Vaccination was more common among women who felt more susceptible to influenza (OR = 1.82, 95% CI 1.10–3.01), who perceived greater vaccine effectiveness (OR = 3.92, 95% CI 1.48–10.43), and whose doctors recommended they have flu shots (OR = 3.06, 95% CI 1.27–7.38). Those who perceived greater barriers of influenza vaccination had lower odds of vaccination (OR = 0.19, 95% CI 0.05–0.75). Perceived social norms, anticipated inaction regret, and worry also predicted uptake, though demographic characteristics of respondents did not.

Conclusion

The HBM provides a valuable framework for exploring influenza vaccination among pregnant women. Our results suggest several potential areas of intervention to improve vaccination rates.     

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.     

Knowledge,attitudes and vaccination coverage of healthcare workers regarding occupational vaccinations

Objectives

Immunization of healthcare workers (HCWs) is a major issue for infection control in healthcare facilities. The aim of this study was to evaluate knowledge regarding occupational vaccinations, HBV, varicella and influenza vaccination rates and attitudes towards influenza vaccine among HCWs.

Design and setting

A cross-sectional survey was conducted in two wards (Medicine and Paediatrics) of a 1182-bed teaching hospital in Paris, France.

Methods

A standardized, anonymous, self-administered questionnaire was used.

Results

Of 580 HCWs, 395 (68%) completed the questionnaire. Knowledge about the occupational vaccinations of HCWs was low. HBV (69%), tuberculosis (54%) and influenza (52%) were the most cited vaccinations. Paediatric staff was more aware of influenza and pertussis immunizations (p < .05). HBV vaccination rate was 93%, among whom 65% were aware of their immune status. Influenza vaccination rate for 2006–2007 was 30% overall, ranging from 50% among physicians to 20% among paramedical staff (p < .05). Physicians based their refusal on doubts about vaccine efficacy, although paramedics feared side effects. Influenza vaccination was associated with knowledge of vaccine recommendations [OR = 1.75, 95% CI: 1.13–2.57] and contact with patients [OR = 3.05, 95% CI: 1.50–5.91].

Conclusions

Knowledge of recommended occupational vaccinations is insufficient in HCWs, except for HBV and influenza. Although the HBV vaccine coverage of HCWs is satisfactory, a large proportion of them is unaware of immune status. Influenza vaccine coverage remains low, especially among paramedical staff because of fear of side effects. As vaccine coverage is associated with knowledge, educational campaigns should be strengthened to increase the adhesion of HCWs to vaccinations.     

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.     

Influenza vaccination and risk of hospitalization among adults with laboratory confirmed influenza illness

Background

Influenza vaccine is moderately effective for preventing influenza illness. It is not known if vaccination reduces the risk of subsequent hospital admission among patients with vaccine failure and laboratory confirmed influenza illness.

Methods

Patients in a community cohort presenting with acute respiratory illness were prospectively enrolled and tested for influenza during 8 seasons to estimate seasonal vaccine effectiveness. Hospital admissions within 14 days after illness onset were identified for all participants aged ≥20 years with laboratory confirmed influenza. The association between vaccination and hospital admission was examined in a propensity score adjusted logistic regression model. The model was validated by examining the association between vaccination and hospital admission in participants without influenza.

Results

Influenza was identified in 1393 (28%) of 4996 participants. Sixty-two (6%) of 1020 with influenza A and 17 (5%) of 369 with influenza B were hospitalized. Vaccination was not associated with a reduced risk of hospital admission among all participants with influenza [adjusted odds ratio (aOR) = 1.08; 95% CI: 0.62, 1.88]; or among those with influenza A (aOR = 1.35; 95% CI: 0.71, 2.57) or influenza B (aOR = 0.67; 95% CI: 0.21, 2.15). Influenza vaccination was not associated with hospitalization after non-influenza respiratory illness (aOR = 1.14; 95% CI: 0.84, 1.54).

Conclusions

Influenza vaccination did not reduce the risk of subsequent hospital admission among patients with vaccine failure. These findings do not support the hypothesis that vaccination mitigates influenza illness severity.     

Health and economic impact of the seasonal influenza vaccination programme in England

Background

The seasonal influenza vaccination programme in England targets individuals over 65 years old and in clinical risk groups.

Methods

A model of influenza transmission and disease was fitted to weekly primary care consultations due to influenza in a typical pre-pandemic season (2006/2007). Different scenarios were constructed about influenza severity and how well vaccines match circulating strains to assess the impact and cost-effectiveness of the current vaccination programme.

Results

A well-matched vaccine may reduce the incidence of laboratory-confirmed influenza illness from 8.2% (95% range 4.3–13%) to 5.9% (95% range 2.9–9.7%), with 56–73% of this due to indirect protection. The programme is likely to be cost-effective unless both low severity and poor matching is assumed.

Conclusion

The current seasonal influenza vaccination programme appears to substantially reduce disease burden and provides good value for money.     

Correlates of general practitioners’ recommendations to patients regarding vaccination for the 2009–2010 pandemic influenza (A/H1N1) in France: Implications for future vaccination campaigns

Background

General practitioners’ (GPs) recommendations to their patients regarding influenza vaccination is a key determinant of patient uptake of influenza vaccination.

Objectives

To study factors associated with GPs’ recommendations regarding pandemic vaccination (pvaccination) to adults ≤65 years of age (hereafter referred to as adults) at risk and not at risk of severe complications of the 2009–2010 A/H1N1 influenza.

Patients/Methods

National cross-sectional survey of 1431 French GPs. Pvaccination recommendations by GPs to adults were studied according to three categories: recommended pvaccination to at-risk adults only; recommended pvaccination to all adults; recommended against pvaccination or did not provide any advice to any adult.

Results

GPs were more likely to recommend pvaccination to at-risk than not-at-risk adults (73.4% vs 40.1%, p < 0.01). GPs who consulted official sources of information rather than news media during the pandemic were more likely to recommend pvaccination to at-risk adults only (OR = 1.78; CI 95% = 1.27–2.48) and to all adults (OR = 2.03; CI 95% = 1.42–2.92) than other GPs. GPs’ unfavorable perceptions of the risk/efficacy balance of the pandemic vaccine (pvaccine) together with their perceptions of the low severity of the disease were negatively associated with recommending pvaccination. Hospitalization of GPs’ patients because of the influenza was specifically associated with pvaccine recommendation to all adults (OR = 2.81; CI 95% = 1.98–3.99) but not with pvaccine recommendation to at-risk adults only.

Conclusion

In the pandemic context, GPs’ perceptions of disease severity and the risk/efficacy balance of the pvaccine were the major determinants of French GPs recommending pvaccination or not. To increase the general public's acceptability of vaccination policies, GPs should be adequately informed about the course of the epidemics and the safety of the vaccine.     

Factors associated with influenza vaccine receipt in community dwelling adults and their children

Background

Factors associated with influenza vaccine receipt are well studied in healthcare personnel, pregnant women, and the elderly. There has been substantially less research in community dwelling adults and children, and none among entire households. Many studies determine vaccination status by self-report or behavioral intention, outcomes susceptible to misclassification. Given that vaccine is recommended for everyone over six months, re-evaluating these factors is warranted.

Methods

The Household Influenza Vaccine Effectiveness (HIVE) study is a prospective cohort of households with children. In 2010–2011, 549 adults representing 312 households completed surveys evaluating knowledge, attitudes, and practices regarding influenza vaccination for themselves and their children. Using the health belief model (HBM) as a framework, we examined factors associated with documented seasonal influenza vaccine receipt using log-binomial regression models.

Results

In multivariate models, cues to action such as doctor recommendation, (RR 1.62, 95% CI: 1.25–2.10), perceived benefits (RR 1.25, 95% CI: 1.04–1.50), and perceived susceptibility (RR 1.21, 95% CI: 1.03–1.42) were significantly associated with increased likelihood of vaccine receipt among adults while high perceived barriers were associated with decreased likelihood (RR 0.38, 95% CI: 0.25–0.59). Similarly, parents reporting higher barriers were less likely (RR 0.58, 95% CI: 0.42–0.79) and those perceiving greater benefits (RR 4.16, 95% CI: 2.28–7.59) and severity (RR 1.13, 95% CI: 1.00–1.27 were more likely to vaccinate their children. The observed effects of perceptions of susceptibility, severity, and benefits were more pronounced at low cues to action for children, as were the effects of perceptions of barriers and severity among adults.

Conclusion

Perceived benefits and barriers are most strongly associated with vaccine receipt. However, the effects of various factors were most pronounced in the absence of cues to action, which may be an important component of targeted interventions.     

Vaccination perceptions of school employees in a rural school district

Background

There continues to be a need for increases in adult vaccination rates, especially among those working in environments which may easily become communicable disease outbreak centers, such as school employees in the school environment. The purpose of this study was to evaluate why rural Utah school employees were non-compliant with the influenza and measles, mumps, and rubella (MMR) vaccines, as well as to identify their views on mandatory vaccination policies.

Methods

A questionnaire was distributed to all school employees in a rural Utah school district. Data analysis included frequencies and measures of central tendency and dispersion for quantitative items and theme identification for qualitative items.

Results

Only 51% of school employees were adequately vaccinated for influenza. Reasons for noncompliance with the influenza vaccine included inconvenience, lack of perceived need, and questionable vaccine efficacy. There were 39.3% school employees who had not received an MMR during adulthood, which was commonly attributed to lack of knowledge regarding the need for this vaccine. Almost half (45.7%) of school employees believed a mandatory vaccination policy should be instituted, although 24.2% of school employees were opposed to mandatory adult vaccination policies. Reasons for opposing vaccination mandates included violation of personal choice, lack of perceived vaccination safety and efficacy, lack of perceived need for adult vaccines, and vaccine cost.

Conclusions

Suboptimal vaccination rates of school employees may negatively affect the health and well-being of individuals in the school environment. School employees report a variety of beliefs regarding the influenza and MMR vaccines. While over half of school employees support mandatory vaccination policies for adults working in the school environment, those opposing such a policy report concerns regarding violation of personal choice. Public health officials and school administrators should coordinate efforts to increase vaccination rates among adults in the school environment.     

High-dose trivalent influenza vaccine compared to standard dose vaccine in elderly adults: Safety,immunogenicity and relative efficacy during the 2009–2010 season

Background

High-dose trivalent influenza vaccine was developed to improve antibody responses to influenza vaccine in the elderly and hence potentially impact favorably on influenza-associated morbidity and mortality in this population.

Methods

A phase IIIb, multicenter, randomized, double-blind, controlled trial was conducted to compare High-Dose (HD) trivalent inactivated influenza vaccine (60 μg of hemagglutinin [HA] per strain) to standard dose (SD) vaccine (15 μg of HA per strain) in adults ≥65 years of age. Assessments of safety (serious adverse events [SAE]), immunogenicity (hemagglutination inhibition [HAI] titers) and relative efficacy were performed during the 2009–2010 influenza season, which coincided with the H1N1 pandemic.

Results

A total of 9172 participants were enrolled in 99 research centers in the US (6117 and 3055 randomized to the HD and SD groups, respectively). Within 180 days after vaccination, 6.7% and 6.5% of participants in the HD and SD vaccine groups, respectively, experienced at least one SAE, of which 0.4% and 0.3% had a fatal outcome. A total of 0.5% of participants in both groups discontinued the study due to a SAE. Post-vaccination HAI titers and rate of post-vaccination HAI titer ≥1:40 were significantly higher in the HD group. No cases of influenza caused by viral types/subtypes similar to those in the vaccines were observed. All cases genetically or antigenically characterized were classified as similar to influenza A/California/7/2009 (H1N1), the pandemic strain. The vaccine efficacy of HD vaccine relative to SD vaccine against any influenza viral type/subtype was 12.6% (95% CI −140.5; 65.8) in the intent-to-treat analysis.

Conclusion

High-dose trivalent inactivated influenza vaccine is safe and well tolerated and provides superior immune responses compared to standard dose vaccine. Demonstration of a superior vaccine efficacy requires a separate large randomized, controlled trial.     

Seasonal influenza vaccine effectiveness in pre- and full-term children aged 6–23 months over multiple seasons

Introduction

This study aimed to determine the effectiveness of seasonal influenza vaccine in pre- and full-term children aged 6–23 months.

Methods

We examined a cohort of 683,354 young children (7.7% preterm) over five influenza seasons (2004–2005 to 2008–2009) in Ontario, Canada. Vaccine effectiveness was estimated using influenza-coded ambulatory visits during virologically-confirmed influenza season periods as the outcome and multivariable Cox proportional hazards modeling.

Results

Full vaccination was associated with a 19% reduction in influenza-coded ambulatory visits (HR = 0.81; 95% CI, 0.68–0.97) in all children, and an 18% reduction in full-term children (HR = 0.82; 95% CI, 0.68–0.99). We did not find significant vaccine effectiveness for preterm children. No benefit was found for partial vaccination.

Conclusions

In children younger than two years, only full influenza vaccination is associated with reduced influenza-coded ambulatory visits. Since the effectiveness of influenza vaccination in preterm children remains uncertain, further study of this highly vulnerable population is warranted.     

Impact of maternal characteristics on the effect of maternal influenza vaccination on fetal outcomes

Background

Maternal infections during pregnancy have been associated with adverse fetal and infant health outcomes, and vaccination against influenza is the most effective tool to prevent morbidity and mortality due to seasonal and pandemic influenza. We evaluated the association between receipt of the inactivated seasonal influenza vaccine on preterm and small for gestational age (SGA) births, with the aim to assess racial and socioeconomic variations in vaccine effect.

Methods

We conducted a retrospective analysis of state-wide surveillance data from Georgia for the most recent four years available at the beginning of the study, a total of 8393 live births in Georgia from January 1, 2005 through December 31, 2008. We constructed multivariable logistic regression models and calculated odds ratios (OR) estimates with corresponding 95% confidence intervals (CI) to evaluate the effect of maternal influenza vaccination on SGA (birth weight <10th percentile for gestational age) and preterm (gestational age at birth <37 weeks) births while controlling for potential confounders.

Results

Among all women, we found significant strong associations between maternal influenza vaccination and reduced odds of a preterm birth during the widespread influenza activity period [OR = 0.39, 95% CI: 0.18, 0.83]. In this period, vaccination was protective against SGA births among women at higher risk for influenza related morbidity – women enrolled in the Women, Infant and Child (WIC) program [OR = 0.20, 95% CI: 0.04, 0.98] and Black women [OR = 0.15 95% CI: 0.02, 0.94]; maternal influenza vaccination was associated with reduced odds of a preterm birth among white women [OR = 0.34, 95% CI: 0.12, 0.91] and women of higher socio-economic status [OR = 0.30, 95% CI: 0.12, 0.74].

Conclusion

Influenza vaccination during pregnancy was significantly associated with reduced odds of small for gestational age and preterm births during the widespread influenza activity period. Vaccination effects varied by socio-demographic characteristics.     

Influenza vaccination during pregnancy: Coverage rates and influencing factors in two urban districts in Sydney

Background

Pregnant women have an increased risk of complications from influenza. Influenza vaccination during pregnancy is considered effective and safe; however estimates of vaccine coverage are low. This study aimed to determine influenza vaccination coverage and factors associated with vaccine uptake in pregnant women in two Sydney-based health districts.

Methods

A random sample of women who delivered a baby in a public hospital in Sydney and South-Western Sydney Local Health Districts between June and September 2012 were surveyed using a computer assisted telephone interviewing service.

Results

Of the 462 participants (participation rate 92%), 116 (25%) reported receiving the influenza vaccine during their pregnancy. In univariate analysis, vaccination coverage varied significantly depending on antenatal care type, hospital of birth, and parity (p<0.05), but not for age category, highest level of education, country of birth, language spoken at home, or Aboriginal status. Women who received antenatal care through a general practitioner (GP) had 2.3 (95% CI 1.4–3.6) times the odds (unadjusted) of receiving the influenza vaccination than those who received their antenatal care through a public hospital. The main reason cited for vaccination was GP recommendation (37%), while non-recommendation (33%) and lack of knowledge (26%) were cited as main reasons for not receiving the vaccination. 30% of women recalled receiving a provider recommendation for the vaccination and these women had 33.0 times the odds (unadjusted) of receiving the vaccination than women who had not received a recommendation. In a multivariate model a provider recommendation was the only variable that was significantly associated with vaccination (OR 41.9; 95% CI 20.7–84.9).

Conclusion

Rates of influenza vaccination during pregnancy are low. There is a significant relationship between healthcare provider recommendation for the vaccination and vaccine uptake. Increasing provider recommendation rates has the potential to increase coverage rates of influenza vaccination in pregnant women.