Parental perceptions of childhood seasonal influenza vaccination in Singapore: A cross-sectional survey

PurposeSeasonal influenza vaccination is recommended in children aged 6–59 months, but little is known about child vaccination coverage and determinants in Asian settings. We report the results of a survey of knowledge, attitudes, practices, and determinants of child influenza vaccination in Singapore.MethodsIn December 2015-March 2016, we conducted a survey of 332 parents of children aged 6 months to 5 years attending pre-schools. We assessed child influenza vaccine coverage and parental knowledge, attitudes, and practices of child influenza vaccination. We used multivariable regression and structural equation models to identify factors associated with child influenza vaccination.ResultsKnowledge about influenza, perceived benefit of vaccination, and willingness to vaccinate were high. However, only 32% of children had ever received influenza vaccine, and only 15% in the past year. Factors independently associated with child influenza vaccination included: being recommended influenza vaccine by a child’s doctor (prevalence ratio (PR) = 2.47, 95% CI: 1.75–3.48); receiving influenza vaccine information from a private general practitioner (PR = 1.47, 95% CI: 1.05–2.04); regularly receiving pre-travel influenza vaccine (PR = 1.64, 95% CI: 1.19–2.25); higher willingness to vaccinate (PR = 1.58, 95% CI:1.24–2.04 per unit increase in willingness score); and feeling well-informed about influenza vaccine (PR = 1.44, 95% CI: 1.04–1.99). Parents who obtained influenza vaccine information from television were less likely to have vaccinated their child (PR = 0.44, 95% CI: 0.23–0.85). Path analysis indicated that being recommended vaccination by a child's doctor increased willingness to vaccinate and self-efficacy (feeling well-informed about influenza vaccine). Median willingness-to-pay for a dose of influenza vaccine was SGD30 (interquartile range: SGD20-SGD50), and was higher in parents of vaccinated compared with unvaccinated children (SGD45 vs SGD30, p = 0.0012).ConclusionKnowledge and willingness to vaccinate was high in this parent population, but influenza vaccine uptake in children was low. Encouraging medical professionals to recommend vaccination of eligible children is key to improving uptake.     

Knowledge,attitudes and practices of Australian medical students towards influenza vaccination

BackgroundAnnual influenza vaccination is recommended but not compulsory for healthcare workers in Australia, including medical students. A quarter of healthcare workers are estimated to have an influenza infection in any given year, with a subsequent transmission risk to colleagues and patients. During clinical placements, medical students are also at risk of influenza. While compliance with other vaccination requirements are high, influenza vaccine uptake of healthcare workers and medical students remain low globally. We aimed to explore medical students’ influenza vaccination rates, attitudes, knowledge and intended practices at a large Australian university.MethodA 35 item self-administered online survey was distributed to medical students enrolled at a large Australian university (UNSW Australia) in April/May 2014. The survey examined the knowledge, attitudes and practices of medical students towards influenza vaccination and identified factors associated with vaccine uptake.ResultsOf the 606 students, 53.8% (95%CI 49.8–57.8%) receiving their most recent influenza vaccine in 2014. Self-protection was the most common motivator (83%) and inconvenience (64%) the most common barrier to vaccination, despite access to on campus clinics. Students generally held positive attitudes to the influenza vaccine and vaccination recommendations, though some misconceptions existed. The majority (61%) were in support of mandatory influenza vaccination policies for medical students. Significant predictors of influenza vaccination included living on campus, clinical experience, awareness of vaccination recommendations and agreeing that vaccination was important for medical students, while those with perceived time constraints were less likely to be vaccinated.ConclusionMisconceptions and access to influenza vaccine were barriers to uptake of influenza vaccine by medical students. Medical programs need to emphasise the benefits of influenza vaccination in the protection of healthcare workers and patient safety across the medical education program. Our results suggesting majority support for mandatory influenza vaccination may represent a shifting perspective in the medical community.     

Knowledge,attitudes and practices about influenza vaccination among pregnant women and healthcare providers serving pregnant women in Managua,Nicaragua

BackgroundNicaragua implemented an influenza vaccination program for pregnant women with high-risk obstetric conditions in 2007. In 2014, the recommendation of influenza vaccination expanded to include all pregnant women. Given the expansion in the recommendation of vaccination, we evaluated knowledge, attitudes and practices of pregnant women and their healthcare providers towards influenza vaccination and its recommendation.MethodsWe conducted surveys among pregnant women and their healthcare providers from June to August 2016 at two hospitals and 140 health facilities in Managua. The questions were adapted from the U.S. national CDC influenza survey and related to knowledge, attitudes and practices about influenza vaccination and barriers to vaccination. We analyzed reasons for not receiving vaccination among pregnant women as well as receipt of vaccination recommendation and offer by their healthcare providers.ResultsOf 1,303 pregnant women enrolled, 42% (5 4 5) reported receiving influenza vaccination in the 2016 season. Of those who reported not receiving vaccination, 46% indicated barriers to vaccination. Pregnant women who were vaccinated were more likely to be aware of the recommendation for vaccination and the risks of influenza illness during pregnancy and to perceive the vaccine as safe and effective, compared to unvaccinated pregnant women (p-values < 0.001). Of the 619 health workers enrolled, over 89% recalled recommending influenza vaccination to all pregnant women, regardless of obstetric risk. Of the 1,223 women who had a prenatal visit between the start date of the influenza vaccination and the time of interview, 44% recalled receiving a recommendation for influenza vaccination and 43% were offered vaccination. Vaccination rates were higher for those receiving a recommendation and offer of vaccination compared with those who received neither (95% vs 5%, p-value < 0.001).ConclusionPregnant women in Managua had positive perceptions of influenza vaccine and were receptive to receiving influenza vaccination, especially after the offer and recommendation by their healthcare providers.     

A cross sectional survey to evaluate knowledge,attitudes and practices regarding seasonal influenza and influenza vaccination among diabetics in Pretoria,South Africa

BackgroundIn South Africa, influenza vaccination is recommended to all diabetics. However, vaccination coverage among diabetics remains low. Therefore, this study aimed to explore the knowledge, attitudes, and practices among people with diabetes in Pretoria regarding seasonal influenza and influenza vaccination.MethodA cross-sectional survey was conducted among type 1 and 2 diabetes mellitus patients who attended diabetic clinics in two major tertiary hospitals in Pretoria, South Africa from October to December 2015. The pilot-tested questionnaire consists of 32 quantitative questions that covered seasonal influenza and influenza vaccination in terms of the patient’s demographics, medical history and knowledge, attitudes and practices.ResultsA total of 292 completed questionnaires were received with a response rate of 70.0%. Of these, 162 participants (55.5%) believed that influenza is the same as common cold. While 96 (32.9%) participants were aware that they were at higher risk of complications of influenza, only 86 (29.5%) participants considered vaccination as an effective means in preventing serious influenza-related complication. Even though 167 (57.2%) participants had heard of the vaccine to prevent influenza, only 84 (28.8%) participants were previously vaccinated. Multivariate analysis shows that participants with good attitude score for influenza vaccination were 18.4 times more likely to be vaccinated compared with those with poor attitude score (OR =18.4, 95%CI. 5.28–64.10, p = .001). Among those previously vaccinated, advice from their doctors (82/84, 97.6%) was the main factor encouraging vaccination. Top reasons given by participants who had never been vaccinated before (208/292, 71.2%) include use of alternative protection (107/208, 51.4%) and that vaccination is not necessary because flu is just a minor illness (93/208, 44.7%).ConclusionUptake of seasonal vaccination among diabetics in Pretoria is low. Level of knowledge and perception are the main barriers to vaccination. Health care provider’s advice may be an important key predictor of previous influenza vaccination and they should continue to educate and encourage all diabetics to get vaccinated for influenza at least once yearly.     

Influenza vaccination in people with type 2 diabetes,coverage, predictors of uptake,and perceptions. Result of the MADIABETES cohort a 7 years follow up study

ObjectivesWe aim to determine influenza vaccination uptake among people with diabetes included in the MADIABETES cohort study in order to identify predictors of uptake and to analyze reasons for adherence and non-adherence with vaccination.MethodsUsing data from the MADIABETES Study we conducted a retrospective case record form based study without controls. We included outpatients with type 2 diabetes mellitus. Information was obtained from computerized clinical records and by telephone survey.The main dependent variables were influenza vaccination uptake in the year 2013 and the reason for receiving or refusing vaccination.ResultsOverall, 65.7% had received the influenza vaccine in 2013. The mean number of influenza vaccines received from 2007 to 2013 was 3.24 (SD1.15), although 19.23% had not received any influenza vaccine and 23.3% had been vaccinated against pneumococcus. The variables that increased the probability of being vaccinated were inclusion in the age-based recommendation (⩾60 years), having a chronic respiratory disease, previous pneumococcal vaccination, higher number of visits to the general practitioner, higher number of influenza vaccines, and longer time since diabetes diagnosis. A higher mean glycated haemoglobin value in 2013 was associated with a reduced probability of vaccination.Most patients (90%) agreed to be vaccinated following their physician’s advice because of their age or their chronic conditions. The most common reason for refusal among men was the belief that they were not at risk (41.6% vs. 29.79% in women); the most common reason for refusal among women was fear of adverse reactions (32.53% vs. 20.23% in men).ConclusionsThe uptake of influenza vaccination among diabetic patients in the present study was below desirable levels. The main barrier to vaccination was lack of knowledge regarding the need for and risks and advantages of influenza vaccination. Healthcare professionals should educate and encourage influenza vaccination among people with diabetes.     

An assessment of parental knowledge,attitudes, and beliefs regarding influenza vaccination

IntroductionSeasonal influenza imposes a significant clinical and economic burden. Despite the availability of an annual vaccine to prevent influenza infection and reduce disease severity, influenza vaccination rates remain suboptimal. Research suggests personal experience, perceived effectiveness, and concerns regarding vaccine safety and side effects are the most influential factors in predicting a parent’s decision to vaccinate. However, current literature is primarily focused on the vaccine decision-making of healthcare workers and those at high risk for influenza complications.MethodsTo assess parental attitudes and beliefs regarding the influenza vaccine, a brief mixed-methods survey was developed and optimized for an electronic platform. The Health Belief Model informed survey design and data analysis. Questions were classified into five core concepts: knowledge, barriers, benefits, experience, and severity. Participants were solicited from a population of parents whose children had participated in a school-based influenza surveillance study (n = 244, 73% response rate). We tested associations between responses and children’s influenza vaccination status the prior season. Categorical questions were tested using Pearson's chi-squared tests and numerical or ordered questions using Mann-Whitney tests. P-values were corrected using the Bonferroni method.ResultsDoubting effectiveness, concerns about side effects, inconvenience, and believing the vaccine is unnecessary were barriers negatively associated with parents’ decision to vaccinate their children during the 2017–18 flu season (p < 0.001). Knowledge that the vaccine is effective in lowering risk, duration, and severity of influenza; receiving the influenza vaccine as an adult; and recognizing the importance of vaccination to prevent influenza transmission in high-risk populations were positively associated with parents’ decision to vaccinate (p < 0.001).ConclusionUnderstanding barriers and motivators behind parents’ decision to vaccinate provides valuable insight that has the potential to shape vaccine messaging, recommendations, and policy. The motivation to vaccinate to prevent influenza transmission in high-risk populations is a novel finding that warrants further investigation.     

Seasonal influenza vaccination in the Americas: Progress and challenges during the COVID-19 pandemic

BackgroundVaccination is one of the most effective measures to prevent influenza illness and its complications; influenza vaccination remained important during the COVID-19 pandemic to prevent additional burden on health systems strained by COVID-19 demand.ObjectivesWe describe policies, coverage, and progress of seasonal influenza vaccination programs in the Americas during 2019–2021 and discuss challenges in monitoring and maintaining influenza vaccination coverage among target groups during the COVID-19 pandemic.MethodsWe used data on influenza vaccination policies and vaccination coverage reported by countries/territories via the electronic Joint Reporting Form on Immunization (eJRF) for 2019–2021. We also summarized country vaccination strategies shared with PAHO.ResultsAs of 2021, 39 (89 %) out of 44 reporting countries/territories in the Americas had policies for seasonal influenza vaccination. Countries/territories adapted health services and immunization delivery strategies using innovative approaches, such as new vaccination sites and expanded schedules, to ensure continuation of influenza vaccination during the COVID-19 pandemic. However, among countries/territories that reported data to eJRF in both 2019 and 2021, median coverage decreased; the percentage point decrease was 21 % (IQR = 0–38 %; n = 13) for healthcare workers, 10 % (IQR = -1.5–38 %; n = 12) for older adults, 21 % (IQR = 5–31 %; n = 13) for pregnant women, 13 % (IQR = 4.8–20.8 %; n = 8) for persons with chronic diseases, and 9 % (IQR = 3–27 %; n = 15) for children.ConclusionsCountries/territories in the Americas successfully adapted influenza vaccination delivery to continue vaccination services during the COVID-19 pandemic; however, reported influenza vaccination coverage decreased from 2019 to 2021. Reversing declines in vaccination will necessitate strategic approaches that prioritize sustainable vaccination programs across the life course. Efforts should be made to improve the completeness and quality of administrative coverage data. Lessons learned from COVID-19 vaccination, such as the rapid development of electronic vaccination registries and digital certificates, might facilitate advances in coverage estimation.     

Impact of prior seasonal influenza vaccination and infection on pandemic A (H1N1) influenza virus replication in ferrets

Early epidemiologic and serologic studies have suggested pre-existing immunity to the pandemic A (H1N1) 2009 influenza virus (H1N1pdm) may be altering its morbidity and mortality in humans. To determine the role that contemporary seasonal H1N1 virus infection or trivalent inactivated vaccine (TIV) might be playing in this immunity we conducted a vaccination-challenge study in ferrets. Vaccination with TIV was unable to alter subsequent morbidity or contact transmission in ferrets following challenge with H1N1pdm. Conversely, prior infection with the contemporary seasonal H1N1 strain altered morbidity, but not transmission, of H1N1pdm despite the detection of only minimal levels of cross reactive antibodies.     

Different influenza vaccine formulations and adjuvants for childhood influenza vaccination

Pediatric influenza is a very common disease: attack rates range from 23% to 48% during interpandemic years and are significantly higher during pandemics. Influenza-related complications seem to be more common in children at risk because of an underlying chronic severe disease, but recently collected data clearly demonstrate that otherwise healthy children can also suffer from severe influenza and that the annual number of deaths is no different between the two groups. The aim of this review is to discuss the characteristics of all influenza vaccines in order to evaluate the real likelihood of prevention, as well as the safety and tolerability of the different formulations and adjuvants. The data indicate that further studies collecting efficacy and effectiveness data and evaluating the immunogenicity and safety of the different formulations and adjuvants should lead to the identification of more ideal influenza vaccines that could be used with significant advantage in the entire pediatric population.     

Factors associated with continued adherence to influenza vaccination in the elderly

Objective

We aimed to analyze the factors influencing continued adherence to influenza vaccination in elderly persons vaccinated in the preceding season.

Methods

Using a population-based vaccination registry, we evaluated the proportion of persons vaccinated against influenza in Navarre, Spain, in the 2010-11 season among non-institutionalized persons aged 65 years or over who had been vaccinated in the 2009-10 season. Logistic regression was used to analyze the influence of sociodemographic, clinical and health care factors.

Results

Of the 64,245 persons vaccinated against influenza in the 2009-10 season, 87% were vaccinated in the 2010-11 season. Continued adherence to vaccination increased with the number of physician visits per year. It was lower in women, in the 65-69 and ≥ 95 year age-groups, in those hospitalized or diagnosed with any major chronic condition in the previous year, and in persons with hematological cancer or dementia. Health districts and physicians with higher coverage in the previous season continued to have higher adherence in the following season.

Conclusions

People vaccinated against influenza in one season tend to be vaccinated in the following one. Sociodemographic, clinical and health care factors have a moderate effect on the continuity of vaccination, with the most important factor being the treating physician.     

Intention to receive influenza vaccination prior to the summer influenza season in adults of Hong Kong, 2015

Following a severe winter epidemic of drifted influenza A(H3N2) during January–March 2015, the Hong Kong government purchased vaccines of southern hemisphere formulation for administration prior to the anticipated summer influenza epidemic. This is the first time that seasonal influenza vaccines will be delivered twice within the same year in Hong Kong. We conducted a household telephone survey to investigate the acceptance of Hong Kong adults to pre-summer influenza vaccination. We found that the proportion of people reporting intention to receive vaccination was 37.8, 24.0, 31.4, and 34.4% in the age groups of 18–39, 40–59, 60–69, and 70 years or above. Only 31.3% of respondents who claimed they were parents or guardians said they would take their children to receive vaccination if the new vaccine was available. These findings suggested that intention to receive pre-summer vaccination was low even among the priority group of older people.     

Does consecutive influenza vaccination reduce protection against influenza: A systematic review and meta-analysis

IntroductionVaccination against influenza on an annual basis is widely recommended, yet recent studies suggest consecutive vaccination may reduce vaccine effectiveness (VE).PurposeTo assess whether when examining the entirety of existing data consecutive influenza vaccination reduces VE compared to current season influenza vaccination.Data sourcesMEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials (CENTRAL) from inception to April 26, 2017; citations of included studies.Study selectionRandomized, controlled trials (RCTs) and observational studies of children, adults and/or the elderly that reported laboratory-confirmed influenza infection over 2 or more consecutive influenza seasons were eligible.Data extractionData related to study characteristics, participant demographics, cases of influenza infection by vaccination group and risk of bias assessment was extracted in duplicate.Data synthesisFive RCTs involving 11,987 participants did not show a significant reduction in VE when participants vaccinated in two consecutive seasons (VE 71%, 95% CI 62–78%) were compared to those vaccinated in the current season (VE 58%, 95% CI 48–66%) (odds ratio [OR] 0.88, 95% CI 0.62–1.26, p = 0.49, I² = 39%). Twenty-eight observational studies involving 28,627 participants also did not show a reduction (VE for two consecutive seasons 41%, 95% CI 30–51% compared to VE for current season 47%, 95% CI 39–54%; OR 1.14, 95% CI 0.98–1.32, p = 0.09, I² = 63%). Results from subgroup analyses by influenza type/subtype, vaccine type, age, vaccine match and co-morbidity support these findings; however, dose–response results were inconsistent. Certainty in the evidence was assessed to be very low due to unexplained heterogeneity and imprecision.LimitationsThe inclusion of studies with relatively small sample sizes and low event rates contributed to the imprecision of summary VE and OR estimates, which were based on unadjusted data.ConclusionAvailable evidence does not support a reduction in VE with consecutive influenza vaccination, but the possibility of reduced effectiveness cannot be ruled out due to very low certainty in this evidence.Funding sourceCIHR Foundation Grant (PROSPERO: CRD42017059893).     

Cost-effectiveness of norovirus vaccination in children in Peru

BackgroundWith candidate norovirus (NV) vaccines in a rapid phase of development, assessment of the potential economic value of vaccine implementation will be necessary to aid health officials in vaccine implementation decisions. To date, no evaluations have been performed to evaluate the benefit of adopting NV vaccines for use in the childhood immunization programs of low- and middle-income countries.MethodsWe used a Markov decision model to evaluate the cost-effectiveness of adding a two-dose NV vaccine to Peru's routine childhood immunization schedule using two recent estimates of NV incidence, one for a peri-urban region and one for a jungle region of the country.ResultsUsing the peri-urban NV incidence estimate, the annual cost of vaccination would be $13.0 million, offset by $2.6 million in treatment savings. Overall, this would result in 473 total DALYs averted; 526,245 diarrhea cases averted;153,735 outpatient visits averted; and 414 hospitalizations averted between birth and the fifth year of life. The incremental cost-effectiveness ratio would be $21,415 per DALY averted; $19.86 per diarrhea case; $68.23 per outpatient visit; and $26,298 per hospitalization. Using the higher jungle NV incidence rates provided a lower cost per DALY of $10,135. The incremental cost per DALY with per-urban NV incidence is greater than three times the 2012 GDP per capita of Peru but the estimate drops below this threshold using the incidence from the jungle setting. In addition to the impact of incidence, sensitivity analysis showed that vaccine price and efficacy play a strong role in determining the level of cost-effectiveness.ConclusionsThe introduction of a NV vaccine would prevent many healthcare outcomes in the Peru and potentially be cost-effective in scenarios with high NV incidence. The vaccine cost-effectiveness model could also be applied to the evaluation of NV vaccine cost-effectiveness in other countries in resource-poor settings, where NV incidence rates are expected to be higher.     

A survey of children's preferences for influenza vaccine attributes

Background

While annual influenza vaccination is recommended by the CDC for children 6 months and older, vaccination rates remain suboptimal. For healthy, US children 2 years of age and older, influenza vaccine is available as an intramuscular injection (TIV) or an intranasal spray (LAIV), respectively. Little is known about children's experiences and preferences for influenza vaccine attributes.

Objective

To examine preferences for influenza vaccine attributes and their relative importance among children.

Methods

A quantitative web-survey was administered to children aged 8-12 years sampled from a standing online panel representative of the US population. Children were stratified by age, gender and parent's influenza vaccination behavior. The survey included questions to ascertain children's preferences for influenza vaccine attributes, including efficacy, chance of common side effects, and mode of administration. It included conjoint (trade-off) questions in which children traded-off different attributes in their choice between two influenza vaccines with differing features. We also surveyed children's comprehension of and ability to complete the conjoint questions.

Results

544 children completed the survey (response rate 37%). Children most frequently selected efficacy as the most important vaccine attribute followed by mode of administration (45% and 31%, respectively). When asked for their preference to receive influenza vaccine as a “shot” or a “nose spray”, the majority (69%) preferred the nose spray. An evaluation of children's ability to complete the conjoint survey demonstrated that 85% of the sample was able to complete the conjoint tasks. Analysis of the conjoint responses demonstrated that mode of administration and efficacy had the greatest impact on preferences, with a relative importance of 40.5% and 30.6%, respectively. In a direct comparison of vaccine profiles representing the efficacy, side effects, and other characteristics of LAIV and TIV, 79% of children preferred the LAIV-like profile.

Conclusion

Children in the sample had consistent opinions regarding influenza vaccine attributes and consider vaccine efficacy and mode of administration to be important. Children can be informed participants in influenza prevention and can be included in discussions regarding influenza vaccination.     

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.     

Impact of seasonal influenza vaccination in the presence of vaccine interference

BackgroundAnnual influenza vaccination is a key to preventing widespread influenza infections. Recent reports of influenza vaccine effectiveness (VE) indicate that vaccination in prior years may reduce VE in the current season, suggesting vaccine interference. The purpose of this study is to evaluate the potential effect of repeat influenza vaccinations in the presence of vaccine interference.MethodsUsing literature-based parameters, an age-structured influenza equation-based transmission model was used to determine the optimal vaccination strategy, while considering the effect of varying levels of interference.ResultsThe model shows that, even in the presence of vaccine interference, revaccination reduces the influenza attack rate and provides individual benefits. Specifically, annual vaccination is a favored strategy over vaccination in alternate years, as long as the level of residual protection is less than 58% or vaccine interference effect is minimal. Furthermore, the negative impact of vaccine interference may be offset by increased vaccine coverage levels.ConclusionsEven in the presence of potential vaccine interference, our work provides a population-level perspective on the potential merits of repeated influenza vaccination. This is because repeat vaccination groups had lower attack rates than groups that omitted the second vaccination unless vaccine interference was at very high, perhaps implausible, levels.     

Negative impact of prior influenza vaccination on current influenza vaccination among people infected and not infected in prior season: A test-negative case-control study in Japan

BackgroundAccumulating evidences indicate that repeated influenza vaccination has negative impact on the vaccine effectiveness (VE). However no published studies considered past influenza infection when assessing the VE of repeated vaccination.MethodsProspective surveillance was conducted from 2009 to 2012 at a community hospital on a small island in Japan. The study included all outpatients with an influenza-like illness (ILI) who attended the hospital, and a rapid diagnostic test (RDT) was used to diagnose influenza A/B infection. The VE of trivalent inactivated influenza vaccine (TIV) against medically attended influenza A (MA-fluA) was estimated using a test-negative case-control study design. The influence of TIV in the prior season on VE in the current season was investigated in the context of MA-fluA during the prior season.ResultsDuring the three influenza seasons, 5838 ILI episodes (4127 subjects) were analysed. Subjects who had an episode of MA-fluA in the prior season were at a significantly lower risk of MA-fluA in the current season (adjusted odds ratio: 0.38, 95% CI: 0.30–0.50). The overall adjusted VE was 28% (95% CI, 14–40). VE was substantially lower in subjects vaccinated in the prior season compared to those who had not been vaccinated in prior season (19%; 95% CI: 0–35 vs 46%; 95% CI: 26–60, test for interaction, P value <0.05). In subjects who did not have MA-fluA in the prior season showed the attenuation of VE due to repeated vaccination (13%; 95% CI: −7 to 30 vs 44%; 95% CI: 24–59, test for interaction, P < 0.05). However this effect was not detected in subjects who had contracted MA-fluA in the prior season.ConclusionsNegative effects of repeated vaccination were significant among those without history of MA-fluA in the prior season.     

Effectiveness of the influenza vaccination program for the elderly in Taiwan

Background and objectives

Since 1998, an influenza vaccination program has been implemented by the Taiwan government targeting people aged ≥65 years. However, the evidence of the effectiveness of this program in preventing influenza, which is based on the nation-wide database, is lacking. This study attempted to estimate the effectiveness of the influenza vaccination program in preventing influenza- and pneumonia-associated outpatient visits and hospitalization in the elderly.

Methods

Randomly sampled data of 1 million claims from the National Health Insurance Research Database compiled into seven consecutive cohorts were used to perform this analysis. Elderly claimants aged ≥65 years were included in each cohort. To decrease potential bias between vaccinated and unvaccinated subjects, the propensity score method was applied. Logistic regression and zero-inflated negative binominal regression were used to examine the effectiveness of vaccination in preventing influenza- and pneumonia-associated outpatient visits and hospitalization.

Results

A significant decrease in both the risk and frequency of hospitalization was observed in elderly people who received influenza vaccination compared with those who did not. No similar decrease was observed in the risk and frequency of outpatient visits for influenza and pneumonia.

Conclusion

Vaccination against influenza reduced hospitalization for influenza and pneumonia in elderly Taiwanese people. These results are meaningful for the promotion of vaccination policy. Annual influenza vaccination of the elderly should be encouraged.