Reduced risk of hospitalization associated with influenza vaccination in Canada

To evaluate the effectiveness of influenza vacation, we conducted analyses at both individual level and health region level. The association between influenza vaccination and hospital admission was examined among 128,677 subjects 12+ years of age who participated in a national survey in 2005. Both influenza and hospital admission proportions varied across health regions. Health regions with higher proportions of influenza vaccination had significantly lower proportions of hospitalization. A 10% increase in influenza vaccination less than 1 year ago was associated with a reduction of 11% in the risk of hospitalization over a 12-month time period at the health region level.     

Influenza vaccination effectiveness in preventing influenza hospitalization in children,Hong Kong,winter 2019/20

The winter influenza season 2019/20 in Hong Kong was predominated by influenza A(H1N1)pdm09. We analysed an on-going test-negative design study consisting of 1227 children admitted for febrile acute respiratory illness from 3 November 2019 (week 45) to 21 March 2020 (week 12). We estimated influenza vaccine effectiveness of 65% (95% CI: 46 – 78) against hospitalization due to influenza A and B combined, and 74% (95% CI: 54 – 85) against hospitalization due to influenza A(H1N1)pdm09.     

湖北省荆州市2010－2012年实验室确诊流感住院率估计

目的 估算2010－2012年湖北省荆州市流感所致严重急性呼吸道感染(SARI)病例的住院率。方法 2010－2012年在湖北省荆州市4家医院的住院病例中开展SARI监测,在患者知情同意后纳入收集人口学、临床表现、治疗情况及转归等信息,并采集呼吸道标本进行流感病毒PCR核酸检测。结果 2010年4月至2012年9月共纳入19 679例SARI病例,为荆州市城区常住居民,其中18 412例(93.6%)采集了鼻咽拭子开展PCR检测,阳性率为13.3%。实验室确诊流感导致的SARI住院率在2010－2012年连续3年的流感季分别为102/10万、132/10万和244/10万。不同的型别/亚型的流感病毒所致的住院率在2010－2011流感季 A(H3N2)为48/10万,A(H1N1)pdm2009为30/10万,B型为24/10万;2011－2012流感季A(H3N2)为42/10万,B型为90/10万;2012年4－9月A(H3N2)为 90/10万,B型为1/10万。A型和B型流感病毒所致住院均主要发生在<5岁年龄组,以0.5～岁组最高。结论 湖北省荆州市流感造成一定住院负担,不同型别/亚型流感在不同流感季会导致不同的住院率,应将<5岁儿童作为流感疫苗接种的重点推荐人群。     

Importance of vaccination habit and vaccine choice on influenza vaccination among healthy working adults

This randomized cluster trial was designed to improve workplace influenza vaccination rates using enhanced advertising, choice of vaccine type (intranasal or injectable) and an incentive. Workers aged 18–49 years were surveyed immediately following vaccination to determine factors associated with vaccination behavior and choice. The questionnaire assessed attitudes, beliefs and social support for influenza vaccine, demographics, and historical, current, and intentional vaccination behavior. Of the 2389 vaccinees, 83.3% received injectable vaccine and 16.7% received intranasal vaccine. Factors associated with previous influenza vaccination were older age, female sex, higher education and greater support for injectable vaccine (all P < .02). Current influenza vaccination with intranasal vaccine vs. injectable vaccine was associated with higher education, the study interventions, greater support for the intranasal vaccine and nasal sprays, less support of injectable vaccine, more negative attitudes about influenza vaccine, and a greater likelihood of reporting that the individual would not have been vaccinated had only injectable vaccine been offered (all P < .01). Intentional vaccine choice was most highly associated with previous vaccination behavior (P < .001). A key to long term improvements in workplace vaccination is to encourage first time influenza vaccination through interventions that include incentives, publicity and vaccine choice.     

Influenza vaccine effectiveness against influenza-associated hospitalization in 2015/16 season,Beijing, China

BackgroundVaccination is recommended to prevent influenza virus infection and associated complications. This study aimed to estimate the influenza vaccine effectiveness (VE) against hospitalization in the 2015/16 season in Beijing.MethodsPatients who were hospitalized in the 5 study hospitals between 1 Oct 2015 and 15 May 2016 were recruited. Influenza vaccination status was obtained for PCR-confirmed influenza patients and the selected controls who tested negative for the virus. Conditional logistic regression was used to estimate the influenza VE matching by calendar week, and adjusting for age, study sites, underlying medical conditions, smoking status, and hospital admissions over the past 12 months.ResultsThe overall VE was −37.9% (95% CI: −103.3, 6.5) against laboratory-confirmed influenza-associated hospitalization. The 2015–16 seasonal vaccine was had −61.9% (95% CI: −211.9, 15.9), −5.4% (95% CI: −108.1, 46.6) and −45.2% (95% CI: −152.6, 16.5) effectiveness to prevent infection from A(H1N1)pdm09, A(H3N2) and influenza B, respectively.ConclusionsInfluenza vaccination did not show effective protection against hospitalization with influenza in 2015/16 season in Beijing.     

Inactivated influenza vaccine effectiveness and an analysis of repeated vaccination for children during the 2016/17 season

ObjectivesWe assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children 6 months to 15 years of age during the 2016/17 season. In addition, we estimated the impact of repeated vaccination in children on VE.MethodsOur study for VEs in preventing influenza and admission due to influenza were conducted according to a test-negative case-control design (TNCC) based on influenza rapid diagnostic test results. We also analyzed the VE by vaccine status in the current and previous seasons for the impact of repeated vaccination.ResultsDuring the 2016/17 season, the quadrivalent IIV was used in Japan. The adjusted VE in preventing influenza illness was 38% (95% CI, 29–46) against influenza A and 39% (95% CI, 18–54) against influenza B. Infants showed no significant VE. The VE in preventing hospitalization was not demonstrated. For the analysis of repeated vaccination, the vaccine was effective only when immunization occurred in the current season. The children who were immunized in two consecutive seasons were more likely to develop influenza compared to those immunized in the current season only (odds ratio, 1.58 [95% CI, 1.05–2.38], adjusted odds ratio, 1.53 [95% CI, 0.99–2.35]). However, the odds ratio of repeated vaccination was not significant when the analysis excluded those who developed influenza in the previous season.ConclusionsVE in children in the 2016/17 season was similar to values previously reported. Repeated vaccination interfered with the VE against any influenza infection in the 2016/17 season. The results of our study suggest that decreased VE by repeat vaccination phenomenon was associated with immunity by influenza infection in the previous season. However, the influenza vaccine should be recommended every season for children.     

Effect of influenza vaccination on hospitalizations in persons aged 50 years and older

Objective

To estimate influenza vaccine effectiveness (VE) in preventing hospitalizations in persons over 50 years of age.

Design

We performed a retrospective, population based study, using a “difference-in-differences” approach to determine the association between hospitalization and prior vaccination. We examined this association when influenza was not circulating and compared it to the association found when influenza was circulating. VE was estimated from the difference in the association between hospitalization and prior vaccination, inside vs. outside influenza seasons.

Setting

Kaiser Permanente in Northern California.

Patients

Health plan members aged 50 years and older during the September 1997 to August 2008 study period, when there were about 68,000 pneumonia hospitalizations in 10 million person-years.

Results

Vaccination was associated with lower risk of hospitalization for pneumonia and influenza, even before flu season, presumably due to unmeasured confounders. When influenza arrived the hospitalization-vaccination association strengthened, yielding an adjusted VE estimate of 12.4% (95% CI: 1.6–22.0) in persons aged 50–64, and 8.5% (95% CI: 3.3–13.5) in those aged 65 years and older. There was no significant effect on hospitalizations for ischemic heart disease (IHD), congestive heart failure (CHF), cerebrovascular disease (CVD), or trauma.

Conclusions

Influenza vaccination has a modest but significant effect on prevention of hospitalization for pneumonia and influenza in persons 50 years of age and older.     

Assessment of temporally-related acute respiratory illness following influenza vaccination

BackgroundA barrier to influenza vaccination is the misperception that the inactivated vaccine can cause influenza. Previous studies have investigated the risk of acute respiratory illness (ARI) after influenza vaccination with conflicting results. We assessed whether there is an increased rate of laboratory-confirmed ARI in post-influenza vaccination periods.MethodsWe conducted a cohort sub-analysis of children and adults in the MoSAIC community surveillance study from 2013 to 2016. Influenza vaccination was confirmed through city or hospital registries. Cases of ARI were ascertained by twice-weekly text messages to household to identify members with ARI symptoms. Nasal swabs were obtained from ill participants and analyzed for respiratory pathogens using multiplex PCR. The primary outcome measure was the hazard ratio of laboratory-confirmed ARI in individuals post-vaccination compared to other time periods during three influenza seasons.ResultsOf the 999 participants, 68.8% were children, 30.2% were adults. Each study season, approximately half received influenza vaccine and one third experienced ≥1 ARI. The hazard of influenza in individuals during the 14-day post-vaccination period was similar to unvaccinated individuals during the same period (HR 0.96, 95% CI [0.60, 1.52]). The hazard of non-influenza respiratory pathogens was higher during the same period (HR 1.65, 95% CI [1.14, 2.38]); when stratified by age the hazard remained higher for children (HR 1·71, 95% CI [1.16, 2.53]) but not for adults (HR 0.88, 95% CI [0.21, 3.69]).ConclusionAmong children there was an increase in the hazard of ARI caused by non-influenza respiratory pathogens post-influenza vaccination compared to unvaccinated children during the same period. Potential mechanisms for this association warrant further investigation. Future research could investigate whether medical decision-making surrounding influenza vaccination may be improved by acknowledging patient experiences, counseling regarding different types of ARI, and correcting the misperception that all ARI occurring after vaccination are caused by influenza.     

Effectiveness of repeated influenza vaccination among the elderly population with high annual vaccine uptake rates during the three consecutive A/H3N2 epidemics

BackgroundAnnually, about 80% of the Korean elderly aged ≥65 years receive influenza vaccination. Repeated annual vaccination has been suggested as an important factor of poor influenza vaccine effectiveness (VE), though reported conflicting results.MethodsDuring the consecutive A/H3N2-dominant influenza seasons between 2012 and 2015, we comparatively evaluated the VE (repeated vs. current season only) against laboratory-confirmed influenza, pneumonia and hospitalization in the elderly aged ≥65 years with influenza-like illness (ILI). Clinical and demographic data were collected prospectively, and vaccination status of prior and current seasons was verified using the immunization registry data of Korean Centers for Disease Control and Prevention.ResultsDuring the first A/H3N2-dominant season in 2012–2013, influenza vaccine showed statistically significant effectiveness against influenza A infection only and when vaccinated in the current season only (VE 53%, 95% CI 15–77). In the latter two seasons (2013–2015 years), the adjusted VE for influenza A was indistinguishable between repeated vaccination and vaccination in the current season only.ConclusionDuring consecutive influenza A/H3N2 epidemics, poor influenza vaccine effectiveness may be more pronounced among the elderly population with a high annual vaccine uptake rate.     

Influenza vaccination among Saudi Hajj pilgrims: Revealing the uptake and vaccination barriers

BackgroundHajj is the world’s largest annual mass gathering that attracts two to three million Muslims from around the globe to a religious assemblage in Makkah, Saudi Arabia. The risk of acquisition and transmission of influenza among Hajj pilgrims is high. Therefore, influenza vaccination is recommended, and was monitored frequently among pilgrims from different countries. However, the vaccination uptake among Saudi pilgrims has not been assessed in recent years.ObjectiveThis analysis aims to evaluate influenza vaccine uptake among Saudi Hajj pilgrims, and identify the key barriers to vaccination.MethodData on influenza vaccination were obtained from Saudi pilgrims who took part in a large trial during the Hajj of 2013, 2014 and 2015. Pilgrims were met and recruited in Mina, Makkah during the peak period of Hajj and were asked to complete a baseline questionnaire that recorded their influenza vaccination history, including reason(s) for non-receipt of vaccine.ResultsA total of 6974 Saudi pilgrims aged between 18 and 95 (median 34) years were recruited; male to female ratio was 1:1.2. Of the total, 90.8% declared their influenza vaccination history, 51.3% of them reported receiving influenza vaccine before travel to Hajj. The vaccination rates for the years 2013, 2014 and 2015 were 21.4%, 48.2% and 58.1%, respectively (P < 0.001). Of 1,269 pilgrims who were at higher risk of severe disease, 54.5% received the vaccine. Lack of awareness (47.5%), reliance on natural immunity (15.8%) and being busy (15.5%) were the main reasons for non-receipt.ConclusionThese data from a convenience sample indicate that influenza vaccine uptake among Saudi Hajj pilgrims is increasing over years but still needs further improvement. Lack of awareness and misperceptions are the main barriers. Education of Saudi pilgrims and health professionals is required to raise awareness about influenza vaccination. Further studies are needed to understand pilgrims’ misperceptions.     

Effects of annual influenza vaccination on mortality and hospitalization in elderly patients with ischemic heart disease: a nationwide population-based study

Objective

The effects of influenza vaccination on ischemic heart disease (IHD) patients remain controversial. The purpose of this study was to evaluate the effects of influenza vaccination on all-cause mortality and hospitalization for cardiovascular disease in elderly IHD patients.

Methods

Elderly patients (> 65 years old) with IHD, including ischemic heart failure and coronary artery disease between January 1997 and September 2002 were identified by using the Taiwan National Health Insurance Research Database. The association between influenza vaccination and all-cause mortality and hospitalization due to cardiovascular disease was analyzed.

Results

We included 5048 patients. During the influenza season, influenza vaccination was associated with a reduced risk of all-cause mortality [hazard ratio (HR), 0.42; 95% confidence interval (CI) 0.35-0.49] and hospitalization for cardiovascular disease (HR, 0.84; 95% CI, 0.76-0.93). During the non-influenza season, vaccination was associated with a reduced risk of mortality (HR, 0.78; 95% CI, 0.68-0.90) in elderly IHD patients.

Conclusion

Influenza vaccination was associated with a reduced risk of all-cause mortality in elderly IHD patients throughout the whole year, as well as a reduced risk of hospitalization during the influenza season.     

Factors associated with influenza vaccination among elderly Spanish women

OBJECTIVES: Influenza vaccination is an effective intervention to diminish morbidity and mortality associated with this disease in aged populations and at-risk groups. The objective of this work was to describe population patterns of vaccination among Galician women and to identify factors associated with vaccination. STUDY DESIGN: Cross-sectional study. METHODS: Cases aged 65 years and over were selected from the Women's Social and Health Interview, Galicia 2000 (n = 1111). The association between influenza vaccination last season and several sociodemographic, lifestyle, health status and health services variables was assessed by logistic regression. RESULTS: In total, 56.3% of cases had received the influenza vaccine. The following variables were significantly associated with vaccination: age 70-74 years (odds ratios, OR=1.56; 95% CI: 1.09-2.26); age> or =75 years (OR=1.88; 95% CI: 1.31-2.71); residence in towns with 5000-20,000 inhabitants (OR=1.79; 95% CI: 1.16-2.77); annual income 6.010 (OR=1.39; 95% CI: 1.01-1.90); unfavourable self-perception of health (OR=1.46; 95% CI: 1.06-2.00); not being a caregiver (OR=1.67; 95% CI: 1.17-2.38); married (OR=1.45; 95% CI: 1.05-2.01); tetanus vaccination (OR=1.43; 95% CI: 1.07-1.93); and visiting a physician in the last 2 years (OR=4.83; 95% CI: 2.61-8.93). CONCLUSIONS: The level of vaccination among Galician women is low, although it is higher than that in Spanish women overall. This work has identified groups of women who are less likely to be vaccinated, and who should be targeted in future vaccination campaigns.     

Knowledge and attitudes towards influenza and influenza vaccination among pregnant women in Kenya

BackgroundInfluenza vaccination during pregnancy benefits mothers and children. Kenya and other low- and middle-income countries have no official influenza vaccination policies to date but are moving towards issuing such policies. Understanding determinants of influenza vaccine uptake during pregnancy in these settings is important to inform policy decisions and vaccination rollout.MethodsWe interviewed a convenience sample of women at antenatal care facilities in four counties (Nairobi, Mombasa, Marsabit, Siaya) in Kenya. We described knowledge and attitudes regarding influenza vaccination and assessed factors associated with willingness to receive influenza vaccine.ResultsWe enrolled 507 pregnant women, median age was 26 years (range 15–43). Almost half (n = 240) had primary or no education. Overall, 369 (72.8%) women had heard of influenza. Among those, 288 (78.1%) believed that a pregnant woman would be protected if vaccinated, 252 (68.3%) thought it was safe to receive a vaccine while pregnant, and 223 (60.4%) believed a baby would be protected if mother was vaccinated. If given opportunity, 309 (83.7%) pregnant women were willing to receive the vaccine. Factors associated with willingness to receive influenza vaccine were mothers’ belief in protective effect (OR 3.87; 95% CI 1.56, 9.59) and safety (OR 5.32; 95% CI 2.35, 12.01) of influenza vaccines during pregnancy.ConclusionApproximately one third of pregnant women interviewed had never heard of influenza. Willingness to receive influenza vaccine was high among women who had heard about influenza. If the Kenyan government recommends influenza vaccine for pregnant women, mitigation of safety concerns and education on the benefits of vaccination could be the most effective strategies to improve vaccine acceptance.     

Comparison of the trivalent live attenuated vs. inactivated influenza vaccines among U.S. military service members

Limited effectiveness data are available comparing live attenuated influenza vaccine (LAIV) to inactivated influenza vaccine (TIV) among adults. To compare the incidence of influenza-like illness following immunization of adults with LAIV vs. TIV, we conducted a retrospective cohort analysis of active component U.S. military personnel for the 2005–2006 and 2006–2007 influenza seasons. Recruits experienced a much higher burden of disease compared to non-recruits, with crude incidence rates of influenza-like illness 2–16 times higher than non-recruits depending on the season and cohort. For both seasons, a slightly greater protection from influenza-like illness was found for non-recruits who received TIV compared to LAIV (adjusted incidence rate ratio, 1.17 (95% CI, 1.14–1.20) and 1.33 (95% CI, 1.30–1.36), 2005–2006 and 2006–2007 influenza seasons, respectively). However, for Army and Air Force recruits, LAIV was found to provide significantly greater protection from influenza-like illnesses compared to TIV, with adjusted incidence rates of influenza-like illness 22–51% and 18–47% lower among LAIV compared to TIV recipients for the 2005–2006 and 2006–2007 influenza seasons, respectively. Possible reasons for differences in recruit and non-recruit findings include differences in pre-existing influenza antibody levels, differing respiratory disease burden, and/or unmeasured confounding. Consideration of these findings should be made when developing influenza immunization policies.     

我国6个省份全人群流感疫苗接种及认知情况调查

目的 了解调查地区全年龄组人群流感预防知识的认知及流感疫苗接种情况，探索影响流感疫苗接种的相关因素。方法 采用横断面调查设计，选择北京市、内蒙古自治区、上海市、广东省、云南省和甘肃省6个省份，通过12320卫生热线采用随机数字表拨打电话的抽样方法，于2018年3-5月开展全年龄组人群的流感防控知识、流感疫苗接种情况的电话调查，调查估计样本量为9 438人。结果 本调查应答率为46.4%（10 045/21 658），10 045名调查对象中，"流感和普通感冒有区别"的知晓率为75.3%（7 564/10 045），"流感病毒会引起严重后果"的知晓率为82.0%（8 241/10 045）。出现流感样症状后采取频繁洗手、戴口罩和自我隔离的健康行为率分别为80.4%（7 936/9 873）、75.8%（7 506/9 899）和73.6%（7 228/9 822）。最近1年流感疫苗接种率为5.7%（570/10 037）。最近1年流感疫苗接种率的相关多因素logistic回归分析结果显示，调查对象来自甘肃省或北京市、职业是医务人员或全日制学生、调查对象共同居住人数≥ 2人、出现流感样症状后戴口罩，最近1年流感疫苗接种率相对较高。结论 6个省份调查对象流感相关知识的知晓率、出现流感相关症状后的健康行为率和最近1年流感疫苗接种率均有待进一步提高。应加强流感预防知识和疫苗接种的健康教育，探索流感疫苗免费接种策略。     

Reduced serologic sensitivity to influenza A virus illness among inactivated influenza vaccinees

We compared ≥4-fold increases in antibody titers by hemagglutination inhibition assay to RT-PCR results among 42 adults with PCR-confirmed influenza A virus illnesses. Serologic sensitivity was higher among unvaccinated (69%, 95% confidence interval [CI] = 48–90%) than vaccinated healthcare personnel (38%, 95% CI = 29–46%) in a 2010–11 prospective cohort.     

Effectiveness and safety of influenza vaccination in children: European perspective

Accumulating evidence for the substantial burden of influenza in children has increased interest in the vaccination of young children against influenza. So far, however, few European countries have issued official recommendations to vaccinate healthy children, which is largely due to the popular belief that inactivated influenza vaccines are ineffective in young children. Virologically confirmed studies performed during different seasons have yielded widely varying estimates for vaccine effectiveness and suggested that the match between the vaccine and the circulating strains of influenza viruses is one of the key drivers of the effectiveness of the vaccine. In seasons with good antigenic match, inactivated influenza vaccines are clearly effective also in children younger than 2 years of age. The live attenuated influenza vaccine provides even greater effectiveness in children, but the overall potential of this vaccine is limited by its licensure for only children older than 2 years of age. The safety record of seasonal inactivated influenza vaccines is excellent even in the youngest children.     

Association between obesity and vulnerability and serologic response to influenza vaccination in older adults

Background

Serologic response to influenza vaccination declines with age. Few other host factors are known to be associated with serologic response. Our objective was to determine whether obesity and vulnerability independently predicted serologic response to influenza vaccination.

Methods

Adults ≥50 years were recruited during the 2008–2009 influenza season. Subjects provided pre- and post-vaccination sera for measuring antibody titers to 2008–2009 vaccine components. Body mass index (BMI) was calculated as weight (kg)/height (m²). Data were collected on vulnerability using the vulnerable elders survey (VES13). Logistic regression evaluated the associations between obesity and vulnerability and the serologic response to vaccination (both seroprotection and seroconversion), adjusting for gender, age, comorbidities, pre-vaccination titer, and site.

Results

Mean (±standard deviation) age of 415 study subjects was 65 ± 10 years; 40% were obese. Mean BMI was 29 ± 5.6 kg/m²; mean VES13 was 1.6 ± 1.8. The proportions of subjects who seroconverted and had seroprotective titers were 40% and 49%, respectively, for A/Brisbane/59 (H1N1); 73% and 80% for A/Brisbane/10 (H3N2); and 34% and 94% for B/Florida. Modified VES-13 (score 0–10, with 10 being most vulnerable) was not associated with seroprotection against H1N1 or H3N2, and VES-13 was directly associated with seroconversion to H1N1 but not H3N2 or B. Obesity (BMI ≥ 30 kg/m² vs. BMI 18.5–30 kg/m²) was not associated with seroprotection for H1N1 or H3N2; obesity was directly associated with seroconversion to H3N2 but not H1N1 or B. Age was inversely associated with seroprotection and seroconversion against H1N1 and with seroconversion to influenza B.

Conclusion

Based on this sample of older healthy subjects, there were no consistent relationships between VES 13 or obesity and either seroprotection or seroconversion to three influenza vaccine antigens.     

Influenza vaccine effectiveness against laboratory-confirmed influenza in a vaccine-mismatched influenza B-dominant season

BackgroundThe 2017–2018 influenza season in Israel was characterized by the predominance of influenza B Yamagata, with a lesser circulation of influenza A(H1N1)pdm09 and influenza A(H3N2). We estimated vaccine effectiveness (VE) of the inactivated influenza vaccine which was selected for use that season.MethodsEnd-of-season VE and 95% confidence intervals (CI) against laboratory-confirmed influenza-like illness (ILI) were estimated by means of the test-negative design. Age-specific VE analysis was carried out using a moving age interval.ResultsSpecimen were obtained from 1,453 community ILI patients; 610 (42.0%) were influenza-positive, among which 69.7% were B, 17.2% A(H1N1)pdm09 and 13.4% A(H3N2). A 98.6% of molecularly characterized influenza B belonged to the Yamagata lineage. Of the sampled individuals, 1320 were suitable for VE analysis. Of those vaccinated, 90.6% received the inactivated trivalent influenza vaccine (TIV) containing a Victoria lineage influenza B-like virus. VE against influenza A differed by age, with the highest VE of 72.9% (95%CI 31.9–89.2%) observed in children 0.5–14 years old, while all ages VE was 46.6% (95%CI 10.4–68.2%). All ages VE against influenza B was 23.2% (95%CI −10.1–46.4%) with age-specific analysis showing non-significant VE estimates. Utilizing a moving age interval of 15 years, afforded a detailed age-specific insight into influenza VE against the influenza viruses circulating during the 2017–2018 season.ConclusionsThe moderate-high 2017–2018 influenza A VE among children and adolescents, supports seasonal influenza vaccination at a young age. The low VE against influenza B in Israel, is most likely the result of influenza B/TIV-mismatch.     

Declining responsiveness to influenza vaccination with progression of human pregnancy

BackgroundInfluenza immunization is universally recommended during pregnancy to protect mothers and their offspring. However, pregnancy-induced shifts in vaccine responsiveness remain poorly defined.MethodsQuantitative and qualitative shifts in the serological response to influenza vaccination were evaluated in healthy women throughout the course of pregnancy. Serum was obtained before and after vaccination among 71 pregnant and 67 non-pregnant women during the 2011–12 and 2012–13 influenza seasons. Serum hemagglutination inhibition (HAI) assay was used to investigate anti-influenza antibody responses by comparing pre-vaccine and post-vaccine geometric mean titers (GMTs) between groups for each antigen. IgG1, IgG2, IgG3, and IgG4 anti-influenza titers were also evaluated by enzyme-linked immunosorbent assay (ELISA). Pregnancy induced shifts in HAI titers and levels of each anti-influenza antibody isotype were evaluated using linear regression models.ResultsPost-vaccine GMTs at day 28 were significantly reduced for women vaccinated during pregnancy for A/California (H1N1) in 2011 (p = 0.027), A/Perth (H3N2) in 2011 (p = 0.037), and B/Wisconsin in 2012 (p = 0.039). Vaccine responses progressively declined with the initiation of vaccination later in pregnancy. Anti-H1N1 IgG1, IgG2, and IgG3 titers were reduced in pregnant women compared to non-pregnant controls, and these titers declined with pregnancy progression. The most striking differences were found for anti-H1N1 IgG1, where titers decreased by approximately 7% each week throughout pregnancy.ConclusionsHAI responses elicited by immunization were significantly reduced during pregnancy for three different influenza vaccine antigens. Anti-H1N1 IgG1 was significantly lower in pregnant women and decreased throughout the course of pregnancy. Waning serological responsiveness to influenza vaccination with the progression of human pregnancy has important translational implications for when immunization should be optimally administered during pregnancy.