Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case-control study

Immune imprinting of SARS-CoV-2 responses: changing first immune impressions

Since the emergence of the ancestral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus and the successful rollout of protective vaccines based on this original strain, SARS-CoV-2 has evolved into several variants, in a classical virus-host arms race typical of RNA viruses, to progressively evade the host immune response. Next-generation bivalent vaccines have been developed with broader protection against emerging variants than the ancestral vaccine. Nonetheless, even these vaccines show lower protection against the latest Omicron variants. Immune printing describes how an immune response to an immunogen is impacted by earlier exposures to a related immunogen. Several lessons about the effect of immune imprinting on responses to SARS-CoV-2 infection and vaccination, including age-associated impacts, can be learned from influenza. Understanding the mechanisms of imprinting of SARS-CoV-2 will be important to inform the design of vaccines that produce broader and more durable protective immune responses to emerging variants.

The Cost of Seasonal Influenza: A Systematic Literature Review on the Humanistic and Economic Burden of Influenza in Older (≥ 65 Years Old) Adults

INTRODUCTION

Adults aged ≥ 65 years contribute a large proportion of influenza-related hospitalizations and deaths due to increased risk of complications, which result in high medical costs and reduced health-related quality of life (HRQoL). Although seasonal influenza vaccines are recommended for older adults, the effectiveness of current vaccines is dependent on several factors including strain matching and recipient demographic factors. This systemic literature review aimed to explore the economic and humanistic burden of influenza in adults aged ≥ 65 years.

METHODS

An electronic database search was conducted to identify studies assessing the economic and humanistic burden of influenza, including influenza symptoms that impact the HRQoL and patient-related outcomes in adults aged ≥ 65 years. Studies were to be published in English and conducted in Germany, France, Spain, and Italy, the UK, USA, Canada, China, Japan, Brazil, Saudi Arabia, and South Africa.

RESULTS

Thirty-eight studies reported on the economic and humanistic burden of influenza in adults aged ≥ 65 years. Higher direct costs were reported for people at increased risk of influenza-related complications compared to those at low risk. Lower influenza-related total costs were found in those vaccinated with adjuvanted inactivated trivalent influenza vaccine (aTIV) compared to high-dose trivalent influenza vaccine (TIV-HD). Older age was associated with an increased occurrence and longer duration of certain influenza symptoms.

CONCLUSION

Despite the limited data identified, results show that influenza exerts a high humanistic and economic burden in older adults. Further research is required to confirm findings and to identify the unmet needs of current vaccines.

Impact of Influenza Vaccination on the Burden of Severe Influenza in the Elderly: Spain, 2017-2020

Annual influenza vaccination is the main strategy to reduce the burden of seasonal influenza epidemics and is recommended for the elderly in most countries with influenza vaccination strategies, with the main objective of preventing hospitalizations and mortality associated with seasonal influenza in this age group. Studies from different countries have estimated the benefits of seasonal influenza vaccination programs in the elderly, preventing a considerable number of cases, hospitalizations and deaths every year. A study measured the number of medically attended confirmed influenza cases in primary care that are prevented annually by vaccination in the population aged 65 and older in Spain, the Netherlands and Portugal, but estimates of the impact of the national influenza vaccination program in the prevention of severe disease in Spain are lacking. The two objectives of this study were to estimate the burden of severe influenza disease in the Spanish population and to measure the impact of influenza vaccination in the prevention of these outcomes in the population aged 65 years and older. Using influenza surveillance systems put in place before the COVID-19 pandemic, we conducted a retrospective observational study to estimate the burden of hospitalizations and ICU admissions in Spain between 2017-18 and 2019-20, by season and age group. Burden estimates for the 65+ group, combined with vaccine effectiveness (VE) and vaccination coverage (VC) data, were used as input data in an ecological, observational study to estimate the impact of the influenza vaccination program on the elderly. We found a higher burden of severe influenza disease in seasons 2017-18 and 2018-19, with A(H3N2) circulation, and in the youngest and oldest age groups. In those aged 65 and older, we estimated an average of 9900 influenza hospitalizations and 1541 ICU admissions averted by vaccination each year. Seasonal influenza vaccination was able to prevent between 11 and 26% influenza hospitalizations and around 40% ICU admissions in the elderly in the three pre-pandemic seasons. In conclusion, our study complements previous analyses in the primary care setting in Spain and demonstrates the benefits of the annual influenza vaccination program in the prevention of severe influenza disease in the elderly, even in seasons with moderate VE.

Duration of influenza vaccine effectiveness in the elderly in Japan: A retrospective cohort study using large-scale population-based registry data

BACKGROUND

The immune response to influenza vaccination in the elderly is likely to be lower than that in young adults. Clinical protection may not persist year-round in the elderly. However, the effectiveness of influenza vaccine in the elderly has not been adequately studied, especially in terms of the duration of effectiveness.

METHODS

We used a linked database of healthcare administrative claims data and vaccination records maintained by the municipality of a city in Kanto region of Japan. We studied individuals who were aged 65 years or older at baseline and were followed up between April 1, 2014 to March 31, 2020. The duration of influenza vaccine effectiveness by age category was analyzed using a time-dependent piecewise Cox proportional hazard model with time-dependent vaccine status, prior season vaccination and covariates confirmed in the baseline period (age, sex, cancer, diabetes, chronic obstructive pulmonary diseases, asthma, chronic kidney diseases, and cardiovascular diseases).

RESULTS

We identified an analysis population of 83,146 individuals, of which 7,401 (8.9%) had experienced influenza and 270 (0.32%) underwent influenza-related hospitalization. Individuals who were vaccinated during the first season (n = 47,338) were older than non-vaccinated individuals (n = 35,808) (average age, 75.8 vs. 74.1 years, respectively). The multivariable analysis showed a lower incidence of influenza in vaccinated individuals (hazard ratio [HR], 0.47; 95% confidence interval [CI], 0.43-0.51; P < 0.001), while the incidence of hospitalization for influenza did not differ significantly by vaccination status (HR, 0.79; 95% CI, 0.53-1.18; P = 0.249). Protective effectiveness against incidence was maintained for 4 or 5 months after vaccination in those aged 65-69 and 80-years, 5 months in 70-79 years.

CONCLUSIONS

Our study identified moderate vaccine effectiveness in preventing the incidence of influenza in the Japanese elderly. Vaccine effectiveness showed a trend of gradual attenuation. Clinicians should suspect influenza infection even in those vaccinated, especially in elderly individuals who had received vaccination more than 4 or 5 months previously.

Does repeated influenza vaccination attenuate effectiveness? A systematic review and meta-analysis

BACKGROUND

Influenza vaccines require annual readministration; however, several reports have suggested that repeated vaccination might attenuate the vaccine's effectiveness. We aimed to estimate the reduction in vaccine effectiveness associated with repeated influenza vaccination.

METHODS

In this systematic review and meta-analysis, we searched MEDLINE, EMBASE, and CINAHL Complete databases for articles published from Jan 1, 2016, to June 13, 2022, and Web of Science for studies published from database inception to June 13, 2022. For studies published before Jan 1, 2016, we consulted published systematic reviews. Two reviewers (EJ-G and EJR) independently screened, extracted data using a data collection form, assessed studies' risk of bias using the Risk Of Bias In Non-Randomized Studies of Interventions (ROBINS-I) and evaluated the weight of evidence by Grading of Recommendations Assessment, Development, and Evaluation (GRADE). We included observational studies and randomised controlled trials that reported vaccine effectiveness against influenza A(H1N1)pdm09, influenza A(H3N2), or influenza B using four vaccination groups: current season; previous season; current and previous seasons; and neither season (reference). For each study, we calculated the absolute difference in vaccine effectiveness (ΔVE) for current season only and previous season only versus current and previous season vaccination to estimate attenuation associated with repeated vaccination. Pooled vaccine effectiveness and ∆VE were calculated by season, age group, and overall. This study is registered with PROSPERO, CRD42021260242.

FINDINGS

We identified 4979 publications, selected 681 for full review, and included 83 in the systematic review and 41 in meta-analyses. ΔVE for vaccination in both seasons compared with the current season was -9% (95% CI -16 to -1, I²=0%; low certainty) for influenza A(H1N1)pdm09, -18% (-26 to -11, I²=7%; low certainty) for influenza A(H3N2), and -7% (-14 to 0, I²=0%; low certainty) for influenza B, indicating lower protection with consecutive vaccination. However, for all types, A subtypes and B lineages, vaccination in both seasons afforded better protection than not being vaccinated.

INTERPRETATION

Our estimates suggest that, although vaccination in the previous year attenuates vaccine effectiveness, vaccination in two consecutive years provides better protection than does no vaccination. The estimated effects of vaccination in the previous year are concerning and warrant additional investigation, but are not consistent or severe enough to support an alternative vaccination regimen at this time.

FUNDING

WHO and the US National Institutes of Health.

Life Satisfaction and Influenza Vaccination Among Older Adults in Canada

Older adults have an increased risk of complications or death from influenza. Despite the benefits of vaccination for older adults, vaccination coverage among older adults ages 65 years and over is still below Canada's national target of 80 per cent. As health-care-seeking behaviours are influenced by several factors, including life satisfaction, we investigated the relationship between life satisfaction and influenza vaccination among older adults. A sample (n = 22,424) from the 2015-2016 Canadian Community Health Survey data was analysed using descriptive and multinomial logistic regression analyses. Higher life satisfaction was associated with a more recent influenza vaccination history. Vaccination differed by gender, age, and self-reported health status, as women, much older adults, and those with the poorest health status were more likely to be vaccinated. The study suggests an association between life satisfaction and influenza vaccination. More research into the factors that impact influenza vaccination in older adults is needed to increase vaccination coverage in the older adult population.

Association between influenza vaccination and SARS-CoV-2 infection and its outcomes: systematic review and meta-analysis

BACKGROUND

World Health Organization recommends that influenza vaccines should benefit as much of the population as possible, especially where resources are limited. Corona virus disease 2019 (COVID-19) has become one of the greatest threats to health systems worldwide. The present study aimed to extend the evidence of the association between influenza vaccination and COVID-19 to promote the former.

METHODS

In this systematic review, four electronic databases, including the Cochrane Library, PubMed, Embase, and Web of Science, were searched for related studies published up to May 2022. All odds ratios (ORs) with 95% confidence intervals (CIs) were pooled by meta-analysis.

RESULTS

A total of 36 studies, encompassing 55,996,841 subjects, were included in this study. The meta-analysis for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection provided an OR of 0.80 (95% CI: 0.73-0.87). The statistically significant estimates for clinical outcomes were 0.83 (95% CI: 0.72-0.96) for intensive care unit admission, 0.69 (95% CI: 0.57-0.84) for ventilator support, and 0.69 (95% CI: 0.52-0.93) for fatal infection, while no effect seen in hospitalization with an OR of 0.87 (95% CI: 0.68-1.10).

CONCLUSION

Influenza vaccination helps limit SARS-CoV-2 infection and severe outcomes, but further studies are needed.

REGISTRATION

PROSPERO, CRD42022333747.

Impact of prior infection and repeated vaccination on post-vaccination antibody titers of the influenza A(H1N1)pdm09 strain in Taiwan schoolchildren: Implications for public health

BACKGROUND

The objective of this study was to evaluate the effects of prior-infection and repeated vaccination on post-vaccination antibody titers.

METHODS

A(H1N1)pdm09 strain was included in 2009 pandemic monovalent, 2010-2011, and 2011-2012 trivalent influenza vaccines (MIVpdm09, TIV10/11, TIV11/12) in Taiwan. During the 2011-2012 influenza season, we conducted a prospective sero-epidemiological cohort study among schoolchildren from grades 1 - 6 in the two elementary schools in Taipei with documented A(H1N1)pdm09 vaccination records since 2009. Serum samples were collected at pre-vaccination, 1-month, and 4-months post-vaccination (T1, T2, T3). Anti-A(H1N1)pdm09 hemagglutination inhibition titers (HI-Ab-titers) were examined. We also investigated the impact of four vaccination histories [(1) no previous vaccination (None), (2) vaccinated in 2009-2010 season (09v), (3) vaccinated in 2010-2011 season (10v), and (4) vaccinated consecutively in 2009-2010 and 2010-2011 seasons (09v + 10v)] and pre-vaccination HI-Ab levels on post-vaccination HI-Ab responses as well as adjusted vaccine effectiveness (aVE) against serologically-defined infection from T2 to T3.

RESULTS

TIV11/12 had zero serious adverse events reported. A(H1N1)pdm09 strain in TIV11/12 elicited seroprotective Ab-titers in 98% of children and showed promising protection (aVE: 70.3% [95% confidence interval (CI): 51.0-82.1%]). Previously unvaccinated but infected children had a 3.96 times higher T2 geometric mean titer (T2-GMT) of HI-Ab than those naïve to A(H1N1)pdm09 (GMT [95% CI]: 1039.7[585.3-1845.9] vs. 262.5[65.9-1045], p = 0.046). Previously vaccinated children with seroprotective T1-Ab-titers had a higher T2-GMT and a greater aVE than those with non-seroprotective T1-Ab-titers. Repeatedly vaccinated children had lower T2-GMT than those receiving primary doses of TIV11/12. However, after controlling prior infection and T1-Ab-titers, differences in T2-GMT among the four vaccination histories became insignificant (p = 0.16).

CONCLUSION

This study supports the implementation of annual mass-vaccination with A(H1N1)pdm09 in schoolchildren for three consecutive influenza seasons when vaccine and circulating strains were well matched, and found that prior infection and pre-vaccination HI-Ab levels positively impacted post-vaccination HI-Ab responses.

Subtype H3N2 Influenza A Viruses: An Unmet Challenge in the Western Pacific

Subtype H3N2 influenza A viruses (A(H3N2)) have been the dominant strain in some countries in the Western Pacific region since the 2009 influenza A(H1N1) pandemic. Vaccination is the most effective way to prevent influenza; however, low vaccine effectiveness has been reported in some influenza seasons, especially for A(H3N2). Antigenic mismatch introduced by egg-adaptation during vaccine production between the vaccine and circulating viral stains is one of the reasons for low vaccine effectiveness. Here we review the extent of this phenomenon, the underlying molecular mechanisms and discuss recent strategies to ameliorate this, including new vaccine platforms that may provide better protection and should be considered to reduce the impact of A(H3N2) in the Western Pacific region.

Enhanced cross protection by hetero prime-boost vaccination with recombinant influenza viruses containing chimeric hemagglutinin-M2e epitopes

Annual repeat influenza vaccination raises concerns about protective efficacy against mismatched viruses. We investigated the impact of heterologous prime-boost vaccination on inducing cross protection by designing recombinant influenza viruses with chimeric hemagglutinin (HA) carrying M2 extracellular domains (M2e-HA). Heterologous prime-boost vaccination of C57BL/6 mice with M2e-HA chimeric virus more effectively induced M2e and HA stalk specific IgG antibodies correlating with cross protection than homologous prime-boost vaccination. Induction of M2e and HA stalk specific IgG antibodies was compromised in 1-year old mice, indicating significant aging effects on priming subdominant M2e and HA stalk IgG antibody responses. This study demonstrates that a heterologous prime-boost strategy with recombinant influenza virus expressing extra M2e epitopes provides more effective cross protection than homologous vaccination.

Sex-specific effects of aging on humoral immune responses to repeated influenza vaccination in older adults

Older adults (≥65 years of age) bear a significant burden of severe disease and mortality associated with influenza, despite relatively high annual vaccination coverage and substantial pre-existing immunity to influenza. To test the hypothesis that host factors, including age and sex, play a role in determining the effect of repeated vaccination and levels of pre-existing humoral immunity to influenza, we evaluated pre- and post-vaccination strain-specific hemagglutination inhibition (HAI) titers in adults over 75 years of age who received a high-dose influenza vaccine in at least four out of six influenza seasons. Pre-vaccination titers, rather than host factors and repeated vaccination were significantly associated with post-vaccination HAI titer outcomes, and displayed an age-by-sex interaction. Pre-vaccination titers to H1N1 remained constant with age. Titers to H3N2 and influenza B viruses decreased substantially with age in males, whereas titers in females remained constant with age. Our findings highlight the importance of pre-existing immunity in this highly vaccinated older adult population and suggest that older males are particularly vulnerable to reduced pre-existing humoral immunity to influenza.

Comparison of Clinical Characteristics for Distinguishing COVID-19 From Influenza During the Early Stages in Guangdong, China

Background: To explore the differences in clinical manifestations and infection marker determination for early diagnosis of coronavirus disease-2019 (COVID-19) and influenza (A and B).

Methods: A hospital-based retrospective cohort study was designed. Patients with COVID-19 and inpatients with influenza at a sentinel surveillance hospital were recruited. Demographic data, medical history, laboratory findings, and radiographic characteristics were summarized and compared between the two groups. The chi-square test or Fisher's exact test was used for categorical variables, and Kruskal–Wallis H-test was used for continuous variables in each group. Receiver operating characteristic curve (ROC) was used to differentiate the intergroup characteristics. The Cox proportional hazards model was used to analyze the predisposing factors.

Results: About 23 patients with COVID-19 and 74 patients with influenza were included in this study. Patients with influenza exhibited more symptoms of cough and sputum production than COVID-19 (p < 0.05). CT showed that consolidation and pleural effusion were more common in influenza than COVID-19 (p < 0.05). Subgroup analysis showed that patients with influenza had high values of infection and coagulation function markers, but low values of blood routine and biochemical test markers than patients with COVID-19 (mild or moderate groups) (p < 0.05). In patients with COVID-19, the ROC analysis showed positive predictions of albumin and hematocrit, but negative predictions of C-reactive protein (CRP), procalcitonin (PCT), lactate dehydrogenase (LDH), hydroxybutyrate dehydrogenase (HBDH), and erythrocyte sedimentation rate. Multivariate analysis revealed that influenza might associate with risk of elevated CRP, PCT, and LDH, whereas COVID-19 might associated with high HBDH.

Conclusion: Patients with influenza had more obvious clinical symptoms but less common consolidation lesions and pleural effusion than those with COVID-19. These findings suggested that influenza likely presents with stronger inflammatory reactions than COVID-19, which provides some insights into the pathogenesis of these two contagious respiratory illnesses.

Repeated influenza vaccination and hospitalization outcomes among older patients with cardiovascular or respiratory diseases

Influenza vaccination in a single season protects against hospitalization outcomes among older adults hospitalized for cardiovascular or respiratory diseases, but the effectiveness of repeated influenza vaccination is less clear. Four hospitalization outcomes (in-hospital death, re-admission, length of stay, and direct medical costs) were extracted from the Beijing Urban Employee Basic Medical Insurance database in 2015-2016 for adults aged ≥60 years hospitalized for cardiovascular or respiratory diseases. Vaccination status during three influenza seasons (2013/2014-2015/2016) was ascertained through linkages to the Beijing Elderly Influenza Vaccination database. The summer months (June-August) were used as a reference period to control unmeasured confounders during the influenza season. There were 99,135 periods of observation in the analysis, with 8.3% participants receiving influenza vaccination in all three seasons. After adjusting for confounders, influenza vaccination in all three seasons was associated with a lower risk of re-admission among patients with cardiovascular diseases (odds ratio 0.71 [95% CI 0.53-0.96]) and a lower risk of death among patients with respiratory diseases (0.68 [0.46-0.98]) compared with those unvaccinated in any season. Among patients with cardiovascular diseases, influenza vaccination in all three seasons was also associated with a non-significant lower risk of death (0.66 [0.44-1.03]) in addition to shorter hospital stays and lower direct medical costs. When stratified by history of vaccination, the effectiveness of current season vaccination was similar among patients with cardiovascular or respiratory diseases (p-value for heterogeneity all >0.05). Repeated influenza vaccination protected against hospitalization outcomes among older adults with cardiovascular or respiratory diseases.

Toxoplasma gondii Infection Inhibits Histone Crotonylation to Regulate Immune Response of Porcine Alveolar Macrophages

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that can infect almost all warm-blooded animals, causing serious public health problems. Lysine crotonylation (Kcr) is a newly discovered posttranslational modification (PTM), which is first identified on histones and has been proved relevant to procreation regulation, transcription activation, and cell signaling pathway. However, the biological functions of histone crotonylation have not yet been reported in macrophages infected with T. gondii. As a result, a total of 1,286 Kcr sites distributed in 414 proteins were identified and quantified, demonstrating the existence of crotonylation in porcine alveolar macrophages. According to our results, identified histones were overall downregulated. HDAC2, a histone decrotonylase, was found to be significantly increased, which might be the executor of histone Kcr after parasite infection. In addition, T. gondii infection inhibited the crotonylation of H2B on K12, contributing on the suppression of epigenetic regulation and NF-κB activation. Nevertheless, the reduction of histone crotonylation induced by parasite infection could promote macrophage proliferation via activating PI3K/Akt signaling pathway. The present findings point to a comprehensive understanding of the biological functions of histone crotonylation in porcine alveolar macrophages, thereby providing a certain research basis for the mechanism research on the immune response of host cells against T. gondii infection.

Behavior of hospitalized severe influenza cases according to the outcome variable in Catalonia, Spain, during the 2017-2018 season

Influenza is an important cause of severe illness and death among patients with underlying medical conditions and in the elderly. The aim of this study was to investigate factors associated with ICU admission and death in patients hospitalized with severe laboratory-confirmed influenza during the 2017–2018 season in Catalonia. An observational epidemiological case-to-case study was carried out. Reported cases of severe laboratory-confirmed influenza requiring hospitalization in 2017–2018 influenza season were included. Mixed-effects regression analysis was used to estimate the factors associated with ICU admission and death. A total of 1306 cases of hospitalized severe influenza cases were included, of whom 175 (13.4%) died and 217 (16.6%) were ICU admitted. Age 65–74 years and ≥ 75 years and having ≥ 2 comorbidities were positively associated with death (aOR 3.19; 95%CI 1.19–8.50, aOR 6.95, 95%CI 2.76–1.80 and aOR 1.99; 95%CI 1.12–3.52, respectively). Neuraminidase inhibitor treatment and pneumonia were negatively associated with death. The 65–74 years and ≥ 75 years age groups were negatively associated with ICU admission (aOR 0.41; 95%CI 0.23–0.74 and aOR 0.30; 95%CI 0.17–0.53, respectively). A factor positively associated with ICU admission was neuraminidase inhibitor treatment. Our results support the need to investigate the worst outcomes of hospitalized severe cases, distinguishing between death and ICU admission.

Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research

The effect of influenza vaccination on influenza severity remains uncertain. We reviewed the literature for evidence to inform the question of whether influenza illness is less severe among individuals who received influenza vaccination compared with individuals with influenza illness who were unvaccinated prior to their illnesses. We conducted a narrative review to identify published findings comparing severity of influenza outcomes by vaccination status among community-dwelling adults and children ≥ 6 months of age with laboratory-confirmed influenza illness. When at least four effect estimates of the same type (e.g., odds ratio) were available for a specific outcome and age category (children versus adults), data were pooled with meta-analysis to generate a summary effect estimate. We identified 38 published articles reporting ≥ 1 association between influenza vaccination status and one of 21 indicators of severity of influenza illness among individuals with laboratory-confirmed influenza. Study methodologies and effect estimates were highly heterogenous, with only five severity indicators meeting criteria for calculating a combined effect. Among eight studies, influenza vaccination was associated with 26% reduction in odds of ICU admission among adults with influenza-associated hospitalization (OR = 0.74, 95% CI 0.58, 0.93). Among five studies of adults with influenza-associated hospitalization, vaccinated patients had 31% reduced risk of death compared with unvaccinated patients (OR = 0.69, 95% CI 0.52, 0.92). Among four studies of children with influenza virus infection, vaccination was associated with an estimated 45% reduction in the odds of manifesting fever (OR = 0.55, 95% CI 0.42, 0.71). Vaccination was not significantly associated with receiving a clinical diagnosis of pneumonia among adults hospitalized with influenza (OR = 0.92, 95% CI 0.82, 1.04) or with risk of hospitalization following outpatient influenza illness among adults (OR = 0.60, 95% CI 0.28, 1.28). Overall, our findings support the hypothesis that influenza vaccination may attenuate the course of disease among individuals with breakthrough influenza virus infection.

Influenza vaccine effectiveness against all-cause mortality following laboratory-confirmed influenza in older adults, 2010-2011 to 2015-2016 seasons in Ontario, Canada

Background

Older adults are at increased risk of mortality from influenza infections. We estimated influenza vaccine effectiveness (VE) against mortality following laboratory-confirmed influenza.

Methods

Using a test-negative design study and linked laboratory and health administrative databases in Ontario, Canada, we estimated VE against all-cause mortality following laboratory-confirmed influenza for community-dwelling adults aged >65 years during the 2010–2011 to 2015–2016 influenza seasons.

Results

Among 54 116 older adults tested for influenza across the 6 seasons, 6837 died within 30 days of specimen collection. Thirteen percent (925 individuals) tested positive for influenza, and 50.6% were considered vaccinated for that season. Only 23.2% of influenza test-positive cases had influenza recorded as their underlying cause of death. Before and after multivariable adjustment, we estimated VE against all-cause mortality following laboratory-confirmed influenza to be 20% (95% confidence interval [CI], 8%–30%) and 20% (95% CI, 7%–30%), respectively. This estimate increased to 34% after correcting for influenza vaccination exposure misclassification. We observed significant VE against deaths following influenza confirmation during 2014–2015 (VE = 26% [95% CI, 5%–42%]). We also observed significant VE against deaths following confirmation of influenza A/H1N1 and A/H3N2, and against deaths with COPD as the underlying cause.

Conclusions

These results support the importance of influenza vaccination in older adults, who account for most influenza-associated deaths annually.

Impact of repeated yearly vaccination on immune responses to influenza vaccine in an elderly population

BACKGROUND

The effectiveness of repeated vaccination for seasonal influenza remains controversial. Here, we measured antibody responses to the influenza virus (A/H1N1, A/H3N2 and B) in a closed cohort of older participants vaccinated against influenza virus in each of 5 consecutive years.

METHODS

One hundred and 11 volunteers aged >61 years were vaccinated subcutaneously with 1 dose (0.5 ml) of inactivated influenza vaccine as recommended by the World Health Organization from the 2005-2006 season through the 2009-2010 season. Hemagglutination inhibition (HI) antibody titers were determined.

RESULTS

HI antibody titers against all 3 virus strains were significantly higher at 4 weeks after vaccination than at a time point prior to vaccination in each of the 5 seasons (P < .01); HI antibody titers were detected at the original prevaccination levels just prior to re-vaccination the following year. Sero-protection and HI antibody titers at 4 weeks after vaccination were similar against all influenza strains and during most of the 5 seasons evaluated. Vaccine strain changes were associated with specific immune responses in 9 of 12 (75%) intervals.

CONCLUSIONS

Taken together, our results suggest that annual vaccination is necessary to maintain humoral immunity for the elderly population. Furthermore, our findings revealed that annual seasonal vaccination was not associated with reduced vaccine effectiveness, and that the reformation of the vaccine resulted in amplified immune responses among those undergoing yearly vaccination in the elderly population.

The Impact of Prior Season Vaccination on Subsequent Influenza Vaccine Effectiveness to Prevent Influenza-related Hospitalizations Over 4 Influenza Seasons in Canada

BACKGROUND

Recent studies have demonstrated the possibility of negative associations between prior influenza vaccines and subsequent influenza vaccine effectiveness (VE), depending on season and strain. We investigated this association over 4 consecutive influenza seasons (2011-2012 through 2014-2015) in Canada.

METHODS

Using a matched test-negative design, laboratory-confirmed influenza cases and matched test-negative controls admitted to hospitals were enrolled. Patients were stratified into 4 groups according to influenza vaccine history (not vaccinated current and prior season [referent], vaccinated prior season only, vaccinated current season only, and vaccinated both current and prior season). Conditional logistic regression was used to estimate VE; prior vaccine impact was assessed each season for overall effect and effect stratified by age (<65 years, ≥65 years) and type/subtype (A/H1N1, A/H3N2, influenza B).

RESULTS

Overall, mainly nonsignificant associations were observed. Trends of nonsignificant decreased VE among patients repeatedly vaccinated in both prior and current season relative to the current season only were observed in the A/H3N2-dominant seasons of 2012-2013 and 2014-2015. Conversely, in 2011-2012, during which B viruses circulated, and in 2013-2014, when A/H1N1 circulated, being vaccinated in both seasons tended to result in a high VE in the current season against the dominant circulating subtype.

CONCLUSIONS

Prior vaccine impact on subsequent VE among Canadian inpatients was mainly nonsignificant. Even in circumstances where we observed a trend of negative impact, being repeatedly vaccinated was still more effective than not receiving the current season's vaccine. These findings favor continuation of annual influenza vaccination recommendations, particularly in older adults.

CLINICAL TRIALS REGISTRATION

NCT01517191.

Influenza vaccine effectiveness against laboratory-confirmed influenza in hospitalised adults aged 60 years or older, Valencia Region, Spain, 2017/18 influenza season

Introduction

Influenza immunisation is recommended for elderly people each season. The influenza vaccine effectiveness (IVE) varies annually due to influenza viruses evolving and the vaccine composition.

Aim

To estimate, in inpatients ≥ 60 years old, the 2017/18 trivalent IVE, overall, by vaccine type and by strain. The impact of vaccination in any of the two previous seasons (2016/17 and 2015/16) on current (2017/18) IVE was also explored.

Methods

This was a multicentre prospective observational study within the Valencia Hospital Surveillance Network for the Study of Influenza and Respiratory Viruses Disease (VAHNSI, Spain). The test-negative design was applied taking laboratory-confirmed influenza as outcome and vaccination status as main exposure. Information about potential confounders was obtained from clinical registries and/or by interviewing patients; vaccine information was only ascertained by registries.

Results

Overall, 2017/18 IVE was 9.9% (95% CI: −15.5 to 29.6%), and specifically, 48.3% (95% CI: 13.5% to 69.1%), −29.9% (95% CI: −79.1% to 5.8%) and 25.7% (95% CI: −8.8% to 49.3%) against A(H1N1)pdm09, A(H3N2) and B/Yamagata lineage, respectively. For the adjuvanted and non-adjuvanted vaccines, overall IVE was 10.0% (95% CI: −24.4% to 34.9%) and 7.8% (95% CI: −23.1% to 31.0%) respectively. Prior vaccination significantly protected against influenza B/Yamagata lineage (IVE: 50.2%; 95% CI: 2.3% to 74.6%) in patients not vaccinated in the current season. For those repeatedly vaccinated against influenza A(H1N1)pdm09, IVE was 46.4% (95% CI: 6.8% to 69.2%).

Conclusion

Our data revealed low vaccine effectiveness against influenza in hospitalised patients ≥60 years old in 2017/18. Prior vaccination protected against influenza A(H1N1)pdm09 and B/Yamagata-lineage.

Effectiveness of influenza vaccine in reducing influenza-associated hospitalizations and deaths among the elderly population; Lazio region, Italy, season 2016-2017

BACKGROUND

This study aimed to estimate influenza vaccine effectiveness (VE) in preventing influenza-related deaths and hospitalizations in the elderly population.

METHODS

We retrospectively analyzed the cohort of 1,251,218 elderly aged ≥65 years who were residing in the Lazio region in 2016-2017. We estimated influenza VE using the Cox proportional hazards model, adjusting for demographic characteristics, preexisting health-risk conditions, and prior vaccinations.

RESULTS

Estimated VE was 14% (95% confidence interval (CI): 11 to 17); 26% (95%CI: 19 to 33) in preventing influenza-related deaths and 13% (95%CI: 10 to 16) in preventing influenza-related hospitalizations. Seasonal VE was higher in the elderly vaccinated in prior seasons (VE = 20%, 95%CI: 17 to 23). We found no significant differences in effectiveness by vaccine type, although the MF59-adjuvanted vaccine appeared more effective than other vaccines in individuals aged ≥75 years, particularly in those aged ≥90 years (VE = 18%, 95%CI: 9 to 26).

CONCLUSIONS

Although VE was low, vaccination still provided benefits in preventing influenza-related hospitalizations and deaths in the elderly, particularly among those vaccinated in prior seasons. Efforts should therefore be made to improve vaccine uptake and the utilization of vaccines with greater effectiveness in the oldest elderly (e.g. high-dose and adjuvanted cell-based vaccines).

Predominance of a Drifted Influenza A (H3N2) Clade and its Association with Age-specific Influenza Vaccine Effectiveness Variations, Influenza Season 2018-2019

Background: Influenza A (H3N2) clade 3C.3a was the predominant influenza virus in Israel throughout the 2018-2019 season, constituting a drift from the influenza A (H3N2) vaccine. We estimated the end-of season vaccine effectiveness (VE) by age, among community patients with influenza-like illness (ILI), considering the hemagglutinin (HA) gene mutations and amino acid substitutions of influenza A (H3N2) viruses detected. Methods: Nose-throat samples were analyzed for the presence of influenza virus, type/subtype, and HA gene sequence. HA gene sequences and amino acid substitutions were compared to the influenza A/Singapore/INFIMH-16-0019/2016 (H3N2)-like 2018-2019 vaccine virus, and a phylogenetic tree was generated. Influenza VE against influenza A (H3N2) was estimated using the test-negative design. VE was estimated by age group and by 15 year moving age intervals. Results: In total, 90% of the influenza A (H3N2) viruses belonged to the 3C.3a clade, constituting a unique situation in the northern hemisphere. Adjusted all-age influenza A (H3N2) VE was −3.5% (95% CI: −51.2 to 29.1). Although adjusted VEs were very low among infants, children, and young adults, a VE of 45% (95% CI: −19.2 to 74.6) was estimated among adults aged ≥45 years old. Conclusions: The higher VE point estimates among older adults may be related to previous exposure to similar influenza viruses.

Impact of national influenza vaccination strategy in severe influenza outcomes among the high-risk Portuguese population

Background

All aged individuals with a chronic condition and those with 65 and more years are at increased risk of severe influenza post-infection complications. There is limited research on cases averted by the yearly vaccination programs in high-risk individuals. The objective was to estimate the impact of trivalent seasonal influenza vaccination on averted hospitalizations and death among the high-risk population in Portugal.

Methods

The impact of trivalent seasonal influenza vaccination was estimated using vaccine coverage, vaccine effectiveness and the number of influenza-related hospitalizations and deaths. The number of averted events (NAE), prevented fraction (PF) and number needed to vaccinate (NVN) were estimated for seasons 2014/15 to 2016/17.

Results

The vaccination strategy averted on average approximately 1833 hospitalizations and 383 deaths per season. Highest NAE was observed in the ≥65 years population (85% of hospitalizations and 95% deaths) and in the 2016/17 season (1957 hospitalizations and 439 deaths). On average, seasonal vaccination prevented 21% of hospitalizations in the population aged 65 and more, and 18.5% in the population with chronic conditions. The vaccination also prevented 29% and 19.5% of deaths in each group of the high-risk population. It would be needed to vaccinate 3360 high-risk individuals, to prevent one hospitalization and 60,471 high-risk individuals to prevent one death.

Conclusion

The yearly influenza vaccination campaigns had a sustained positive benefit for the high-risk population, reducing hospitalizations and deaths. These results can support public health plans toward increased vaccine coverage in high-risk groups.

[Influenza]

BACKGROUND

The influenza virus (IV)-associated mortality and morbidity remains high in Europe.

OBJECTIVE

This article gives an overview of the pathogenesis, diagnostics and treatment optimization strategies according to the currently existing guidelines and clinical trials.

MATERIAL AND METHODS

Literature search and analysis of national and international guidelines for the epidemiology, diagnostics, treatment and prevention of IV infections.

RESULTS AND CONCLUSION

Although the incidence of IV infections remains underrecognized, it is the leading infectious disease-associated cause of mortality and morbidity in Europe. Viruses are mainly transmitted by aerosol inhalation and can cause a wide spectrum of symptoms, ranging from mild signs of a cold to severe respiratory failure requiring mechanical ventilation. The clinical diagnosis should be verified through a PCR-based test in patients with indications for treatment. Neuraminidase inhibitors are currently the treatment of choice for IV infections. Seasonal influenza vaccination is an efficient preventive method. It is therefore imperative to improve vaccination rates in Germany, which have been continuously declining since the pandemic of 2009/2010.

Dose-Dependent Negative Effects of Prior Multiple Vaccinations Against Influenza A and Influenza B Among Schoolchildren: A Study of Kamigoto Island in Japan During the 2011-2012, 2012-2013, and 2013-2014 Influenza Seasons

Background

We investigated the negative effects of prior multiple vaccinations on influenza vaccine effectiveness (VE) and analyzed the association of VE with prior vaccine doses.

Methods

Patients aged 9-18 years presenting with influenza-like illness at a community hospital on a remote Japanese island during the 2011-2012, 2012-2013, and 2013-2014 influenza seasons were tested for influenza using a rapid diagnostic test (RDT). A test-negative, case-control study design was used to estimate the VEs of trivalent inactivated influenza vaccine. Histories of vaccination and medically attended influenza (MA-flu) A and B during 3 previous seasons were collected from registry systems. VE was calculated using multilevel mixed-effects logistic regression models adjusted for the history of RDT-confirmed MA-flu.

Results

During 3 influenza seasons, 1668 influenza-like illness episodes were analyzed, including 421 and 358 episodes of MA-fluA and MA-fluB, respectively. The adjusted VE (95% confidence interval) yielded significant dose-dependent attenuations by prior vaccinations against both MA-fluA (0 doses during previous 3 seasons: 96% [69%-100%], 1 dose: 48% [-7% to 74%], 2 doses: 52% [11%-74%], 3 doses: 21% [-25% to 51%]; P for trend < .05) and MA-fluB (0 doses: 66% [-5% to 89%], 1 dose: 48% [-14% to 76%], 2 doses: 34% [-33% to 67%], 3 doses: -7% [-83% to 37%]; P for trend < .05). After excluding episodes of MA-flu during prior 3 seasons, similar trends were observed.

Conclusions

Repeated previous vaccinations over multiple seasons had significant dose-dependent negative impacts on VE against both MA-fluA and MA-fluB. Further studies to confirm this finding are necessary.

Repeated vaccination against matched H3N2 influenza virus gives less protection than single vaccination in ferrets

Epidemiological studies suggest that humans who receive repeated annual immunization with influenza vaccine are less well protected against influenza than those who receive vaccine in the current season only. To better understand potential mechanisms underlying these observations, we vaccinated influenza-naive ferrets either twice, 10 months apart (repeated vaccination group; RV), or once (current season only group; CS), using a prime-boost regimen, and then challenged the ferrets with A/Hong Kong/4801/2014(H3N2). Ferrets that received either vaccine regimen were protected against influenza disease and infection relative to naive unvaccinated ferrets, but the RV group shed more virus, especially at the peak of virus shedding 2 days post infection (p < 0.001) and regained weight more slowly (p < 0.05) than those in the CS group. Qualitative, rather than quantitative, differences in the antibody response may affect protection after repeated influenza vaccination.

[Prevalence of influenza vaccination in elderly Brazilian with chronic diseases]

This study aimed to estimate the prevalence of influenza vaccination in elderly Brazilians with specific chronic diseases. The sample included individuals 60 years or older (n = 23,815) participating in the National Health Survey (PNS) in 2013. The study estimated the prevalence rates for influenza vaccination and the respective 95% confidence intervals (95%CI). The associations were verified with the chi-square test (Rao-Scott) with 5% significance. Prevalence of influenza vaccination in the elderly was 73.1% (95%CI: 72.0-74.1), and there was no significant difference in prevalence rates between men and women (p = 0.237). Statistically significant differences were observed in prevalence rates for elderly that reported arterial hypertension, 75% (p < 0.001), diabetes mellitus, 76.5% (p = 0.009), cardiac disease, 79.2% (p < 0.001), and lung disease or chronic obstructive pulmonary disease (COPD), 87% (p = 0.001). The results showed low prevalence of vaccination in elderly with some specific chronic diseases for whom there is formal recommendation to receive the vaccine, suggesting the need for a vaccination campaign to extrapolate the age cutoff (elderly) and better targeting to these specific subgroups.

Incidence and seasonality of respiratory viruses causing acute respiratory infections in the Northern United Arab Emirates

Background

The data on the seasonality of respiratory viruses helps to ensure the optimal vaccination period and to monitor the possible outbreaks of variant type.

Objectives

This study was designed to describe the molecular epidemiology and seasonality of acute respiratory infection (ARI)‐related respiratory viruses in the United Arab Emirates (UAE).

Methods

Both upper and lower respiratory specimens were collected for the analysis from all the patients who visited the Sheikh Khalifa Specialty Hospital (SKSH) with ARI for over 2 years. The multiplex real‐time reverse transcription polymerase chain reaction (rRT‐PCR) test was used to detect respiratory viruses, which include human adenovirus, influenza virus (FLU) A and B, respiratory syncytial virus, parainfluenza viruses, human rhinovirus (HRV), human metapneumovirus, human enterovirus, human coronavirus, and human bocavirus.

Results

A total of 1,362 respiratory samples were collected from 733 (53.8%) male and 629 (46.2%) female patients with ARI who visited the SKSH between November 2015 and February 2018. The rRT‐PCR test revealed an overall positivity rate of 37.2% (507/1362). The positive rate increased during winter; it was highest in December and lowest in September. FLU was the most frequently detected virus (273/1362 [20.0%]), followed by human rhinovirus (146/1362 [10.7%]). The FLU positivity rate showed two peaks, which occurred in August and December. The peak‐to‐low ratio for FLU was 2.26 (95% confidence interval: 1.52‐3.35).

Conclusions

The pattern of FLU in the UAE parallels to that of temperate countries. The trend of the small peak of FLU in the summer suggests a possibility of semi‐seasonal pattern in the UAE.

Detection of Respiratory Viruses in Deceased Persons, Spain, 2017

During the 2016–17 influenza season in Spain, we tested specimens from 57 elderly deceased persons for respiratory viruses. Influenza viruses were detected in 18% of the specimens and any respiratory virus in 47%. Only 7% of participants had received a diagnosis of infection with the detected virus before death.

Association of Consecutive Influenza Vaccinations and Pneumonia: A Population-Based Case-Control Study

The purpose of this study was to investigate whether individuals receiving influenza vaccines have a lower risk of pneumonia. A nationwide population-based case-control study was conducted using data from the National Health Insurance Research Database in Taiwan. We enrolled 7565 patients each in pneumonia and non-pneumonia groups after diagnosis of patients with chronic pulmonary disease, and these patients were individually age and sex matched in a 1:1 ratio. Using conditional logistic regression analysis, adjusted odds ratios (aORs) were estimated in patients who received influenza vaccination and those who had not previously had pneumonia. Moreover, we also analyzed the interval between vaccination and the onset of pneumonia and the number of vaccinations received by patients. This was compared with patients who never received influenza vaccination. Patients who had received influenza vaccination and had been vaccinated for two consecutive years (aOR = 0.85, confidence interval (CI) = 0.79–0.93 and aOR = 0.75, CI = 0.67–0.85, respectively) showed lower rates of pneumonia occurrence by 15–25%. In conclusion, influenza vaccination significantly reduces the occurrence of pneumonia, especially in individuals who receive vaccination in consecutive years.

Influenza vaccine effectiveness to prevent influenza-related hospitalizations and serious outcomes in Canadian adults over the 2011/12 through 2013/14 influenza seasons: A pooled analysis from the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS Network)

BACKGROUND

Ongoing assessment of influenza vaccine effectiveness (VE) is critical to inform public health policy. This study aimed to determine the VE of trivalent influenza vaccine (TIV) for preventing influenza-related hospitalizations and other serious outcomes over three consecutive influenza seasons.

METHODS

The Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network (CIRN) conducted active surveillance for influenza in adults ≥16 years (y) of age during the 2011/2012, 2012/2013 and 2013/2014 seasons in hospitals across Canada. A test-negative design was employed: cases were polymerase chain reaction (PCR)-positive for influenza; controls were PCR-negative for influenza and were matched to cases by date, admission site, and age (≥65 y or <65 y). All cases and controls had demographic and clinical characteristics (including influenza immunization status) obtained from the medical record. VE was estimated as 1-OR (odds ratio) in vaccinated vs. unvaccinated patients × 100%. The primary outcome was VE of TIV for preventing laboratory-confirmed influenza-related hospitalization; secondary outcomes included VE of TIV for preventing influenza-related intensive care unit (ICU) admission/mechanical ventilation, and influenza-related death.

RESULTS

Overall, 3394 cases and 4560 controls were enrolled; 2078 (61.2%) cases and 2939 (64.5%) controls were ≥65 y. Overall matched, adjusted VE was 41.7% (95% Confidence Interval (CI): 34.4-48.3%); corresponding VE in adults ≥65 y was 39.3% (95% CI: 29.4-47.8%) and 48.0% (95% CI: 37.5-56.7%) in adults <65 y, respectively. VE for preventing influenza-related ICU admission/mechanical ventilation in all ages was 54.1% (95% CI: 39.8-65.0%); in adults ≥65 y, VE for preventing influenza-related death was 74.5% (95% CI: 44.0-88.4%).

CONCLUSIONS

While effectiveness of TIV to prevent serious outcomes varies year to year, we demonstrate a statistically significant and clinically important TIV VE for preventing hospitalization and other serious outcomes over three seasons. Public health messaging should highlight the overall benefit of influenza vaccines over time while acknowledging year to year variability. ClinicalTrials.gov Identifier: NCT01517191.