Vaccination Schedules

2019 ◽  
Author(s):  
Gee Yen Shin
Keyword(s):  
Hepatitis B ◽  
Influenza Vaccine ◽  
Influenza A ◽  
Online Version ◽  
Influenza B ◽  
Immunisation Schedule ◽  
Influenza A H1n1 ◽  
Green Book ◽  
H3n2 Influenza ◽  
The Uk

The vaccines included in the current UK Immunisation Schedule offer protection against the following pathogens: A. Viruses ● Measles ● Mumps ● Rubella ● Polio ● Human Papilloma Virus (certain serotypes) ● Rotavirus ● Influenza virus (flu A and B) ● Varicella zoster virus (shingles) ● Hepatitis B virus B. Bacteria ● Corynebacterium diphtheriae (Diphtheria) ● Clostridium tetani (Tetanus) ● Bordetella pertussis (Pertussis) ● Haemophilus influenzae type B (Hib) ● Neisseria meningitidis (Meningococcal disease—certain serotypes) ● Streptococcus pneumoniae (Pneumococcal disease—certain serotypes) The UK Immunisation Schedule has evolved over several decades and reflects changes in vaccine development and commercial availability, national and sometimes international disease epidemiology, and the latest expert opinion. It is designed to offer optimal protection against infectious diseases of childhood to infants and children at the most appropriate age. The most up-to-date information about the UK Immunisation Schedule is available on the online version of the Department of Health publication commonly known as the ‘Green Book’: Immunisation Against Infectious Disease Handbook (see Further reading. Various chapters of the online version are updated at regular intervals; thus, it is very important to refer to the online version of the Green Book on the website for current guidance. Changes to the UK Immunisation Schedule are made on the recommendation of the independent Joint Committee on Vaccines and Immunisation (JCVI). Several of the UK Immunisation Schedule vaccines are combined vaccines: ● Measles, mumps, and rubella (MMR). ● Hexavalent diphtheria, tetanus, acellular pertussis, inactivated polio virus, Haemophilus influenza type b, hepatitis B (DTaP/IPV/Hib/HepB). ● Diphtheria, tetanus, acellular pertussis, inactivated polio, and Haemophilus influenzae (DTaP/IPV/Hib). ● Diphtheria, tetanus, acellular pertussis, inactivated polio (DTaP/IPV). ● Tetanus, diphtheria, and inactivated polio (Td/IPV). ● Inactivated influenza vaccine: influenza A H1N1, H3N2, influenza B. ● Live attenuated intranasal influenza vaccine: influenza A H1N1, H3N2, influenza B. In the UK, vaccines against single pathogens covered by the MMR vaccine are not recommended and not available in the National Health Service (NHS). There has been some limited demand for single-target vaccines, e.g. measles, due to misguided and unfounded concerns about the alleged risks of autism following MMR.

scholarly journals Effectiveness of seasonal influenza vaccine for adults and children in preventing laboratory-confirmed influenza in primary care in the United Kingdom: 2015/16 end-of-season results

2016 ◽  
Vol 21 (38) ◽  
Author(s):  
Richard Pebody ◽  
Fiona Warburton ◽  
Joanna Ellis ◽  
Nick Andrews ◽  
Alison Potts ◽  
...  
Keyword(s):  
Primary Care ◽  
United Kingdom ◽  
Influenza Vaccine ◽  
Influenza A ◽  
Immunisation Programme ◽  
Influenza B ◽  
Live Attenuated Influenza Vaccine ◽  
The United Kingdom ◽  
Influenza A H1n1 ◽  
The Uk

The United Kingdom (UK) is in the third season of introducing universal paediatric influenza vaccination with a quadrivalent live attenuated influenza vaccine (LAIV). The 2015/16 season in the UK was initially dominated by influenza A(H1N1)pdm09 and then influenza of B/Victoria lineage, not contained in that season’s adult trivalent inactivated influenza vaccine (IIV). Overall adjusted end-of-season vaccine effectiveness (VE) was 52.4% (95% confidence interval (CI): 41.0–61.6) against influenza-confirmed primary care consultation, 54.5% (95% CI: 41.6–64.5) against influenza A(H1N1)pdm09 and 54.2% (95% CI: 33.1–68.6) against influenza B. In 2–17 year-olds, adjusted VE for LAIV was 57.6% (95% CI: 25.1 to 76.0) against any influenza, 81.4% (95% CI: 39.6–94.3) against influenza B and 41.5% (95% CI: −8.5 to 68.5) against influenza A(H1N1)pdm09. These estimates demonstrate moderate to good levels of protection, particularly against influenza B in children, but relatively less against influenza A(H1N1)pdm09. Despite lineage mismatch in the trivalent IIV, adults younger than 65 years were still protected against influenza B. These results provide reassurance for the UK to continue its influenza immunisation programme planned for 2016/17.

scholarly journals Waning Vaccine Effectiveness Against Influenza-Associated Hospitalizations Among Adults, 2015–2016 to 2018–2019, United States Hospitalized Adult Influenza Vaccine Effectiveness Network

2021 ◽  
Author(s):  
Jill M Ferdinands ◽  
Manjusha Gaglani ◽  
Emily T Martin ◽  
Arnold S Monto ◽  
Donald Middleton ◽  
...  
Keyword(s):  
United States ◽  
Influenza Vaccine ◽  
Influenza A ◽  
Vaccine Effectiveness ◽  
Influenza B ◽  
Influenza A H1n1 ◽  
H3n2 Influenza

Abstract We observed decreased effectiveness of influenza vaccine with increasing time since vaccination for prevention of influenza A(H3N2), influenza A(H1N1)pdm09, and influenza B/Yamagata–associated hospitalizations among adults. Maximum vaccine effectiveness (VE) was observed shortly after vaccination, followed by an absolute decline in VE of about 8%–9% per month postvaccination.

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

2019 ◽  
Vol 24 (31) ◽  
Author(s):  
Ainara Mira-Iglesias ◽  
F Xavier López-Labrador ◽  
Víctor Baselga-Moreno ◽  
Miguel Tortajada-Girbés ◽  
Juan Mollar-Maseres ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Influenza A ◽  
Vaccine Effectiveness ◽  
Influenza Viruses ◽  
Influenza B ◽  
Current Season ◽  
Hospitalised Patients ◽  
Influenza A H1n1 ◽  
Vaccine Type ◽  
The Impact

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.

scholarly journals Uptake and effectiveness of influenza vaccine in those aged 65 years and older in the United Kingdom, influenza seasons 2010/11 to 2016/17

2018 ◽  
Vol 23 (39) ◽  
Author(s):  
Richard G Pebody ◽  
Fiona Warburton ◽  
Nick Andrews ◽  
Mary Sinnathamby ◽  
Ivelina Yonova ◽  
...  
Keyword(s):  
United Kingdom ◽  
Influenza Vaccine ◽  
Influenza A ◽  
Vaccine Uptake ◽  
Attributable Mortality ◽  
Influenza B ◽  
Age Group ◽  
The United Kingdom ◽  
Negative Case ◽  
Influenza A H1n1

Background In 2016/17, seasonal influenza vaccine was less effective in those aged 65 years and older in the United Kingdom. We describe the uptake, influenza-associated mortality and adjusted vaccine effectiveness (aVE) in this age group over influenza seasons 2010/11–2016/17. Methods: Vaccine uptake in 2016/17 and five previous seasons were measured using a sentinel general practitioners cohort in England; the test-negative case-control design was used to estimate pooled aVE by subtype and age group against laboratory-confirmed influenza in primary care from 2010–2017. Results: Vaccine uptake was 64% in 65–69-year-olds, 74% in 70–74-year-olds and 80% in those aged 75 and older. Overall aVE was 32.5% (95% CI: 11.6 to 48.5); aVE by sub-type was 60.8% (95% CI: 33.9 to 76.7) and 50.0% (95% CI: 21.6 to 68.1) against influenza A(H1N1)pdm09 and influenza B, respectively, but only 5.6% (95% CI: - 39.2 to 35.9) against A(H3N2). Against all laboratory-confirmed influenza aVE was 45.2% (95% CI: 25.1 to 60.0) in 65–74 year olds; - 26.2% (95% CI: - 149.3 to 36.0) in 75–84 year olds and - 3.2% (95% CI: - 237.8 to 68.5) in those aged 85 years and older. Influenza-attributable mortality was highest in seasons dominated by A(H3N2). Conclusions: Vaccine uptake with non-adjuvanted, normal-dose vaccines remained high, with evidence of effectiveness against influenza A(H1N1)pdm09 and B, though poor against A(H3N2), particularly in those aged 75 years and older. Forthcoming availability of newly licensed vaccines with wider use of antivirals can potentially further improve prevention and control of influenza in this group.

scholarly journals Age-specific vaccine effectiveness of seasonal 2010/2011 and pandemic influenza A(H1N1) 2009 vaccines in preventing influenza in the United Kingdom

2012 ◽  
Vol 141 (3) ◽  
pp. 620-630 ◽  
Author(s):  
R. G. PEBODY ◽  
N. ANDREWS ◽  
D. M. FLEMING ◽  
J. McMENAMIN ◽  
S. COTTRELL ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Pandemic Influenza ◽  
Influenza A ◽  
Vaccine Effectiveness ◽  
Influenza B ◽  
The United Kingdom ◽  
Previous Season ◽  
Negative Case ◽  
Influenza A H1n1 ◽  
Control Study

SUMMARYAn analysis was undertaken to measure age-specific vaccine effectiveness (VE) of 2010/11 trivalent seasonal influenza vaccine (TIV) and monovalent 2009 pandemic influenza vaccine (PIV) administered in 2009/2010. The test-negative case-control study design was employed based on patients consulting primary care. Overall TIV effectiveness, adjusted for age and month, against confirmed influenza A(H1N1)pdm 2009 infection was 56% (95% CI 42–66); age-specific adjusted VE was 87% (95% CI 45–97) in <5-year-olds and 84% (95% CI 27–97) in 5- to 14-year-olds. Adjusted VE for PIV was only 28% (95% CI −6 to 51) overall and 72% (95% CI 15–91) in <5-year-olds. For confirmed influenza B infection, TIV effectiveness was 57% (95% CI 42–68) and in 5- to 14-year-olds 75% (95% CI 32–91). TIV provided moderate protection against the main circulating strains in 2010/2011, with higher protection in children. PIV administered during the previous season provided residual protection after 1 year, particularly in the <5 years age group.

scholarly journals 2553. Individual Patient-Level Data Meta-Analysis of Live Attenuated and Inactivated Influenza Vaccine Effectiveness Among US Children, 2013–2014 Through 2015–2016

2018 ◽  
Vol 5 (suppl_1) ◽  
pp. S68-S68
Author(s):  
Jessie Chung ◽  
Brendan Flannery ◽  
Rodolfo Begue ◽  
Herve Caspard ◽  
Laurie Demarcus ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Influenza A ◽  
The United States ◽  
Vaccine Effectiveness ◽  
Vaccination Status ◽  
Influenza B ◽  
Rt Pcr ◽  
Current Season ◽  
Influenza A H1n1 ◽  
Vaccine Type

Abstract Background Quadrivalent live attenuated influenza vaccine (LAIV4) was not recommended for use in the United States for the 2016–2017 and 2017–2018 influenza seasons based on US observational studies of vaccine effectiveness (VE) from 2013–2014 to 2015–2016. We pooled individual patient data on children aged 2–17 years enrolled in 5 US studies during these 3 influenza seasons to further investigate VE by vaccine type. Methods Analyses included 17,173 children enrolled in the US Department of Defense Global Laboratory-based Influenza Surveillance Program, US Influenza Vaccine Effectiveness Network, Influenza Incidence Surveillance Project, Influenza Clinical Investigation for Children, and a Louisiana State University study. Participants’ specimens were tested for influenza by reverse transcription-polymerase chain reaction (RT-PCR), culture, or a combination of rapid antigen testing and RT-PCR. VE was calculated by comparing odds of vaccination with either inactivated influenza vaccine (IIV) or LAIV4 among influenza-positive cases to test-negative controls and calculated as 100 × (1 − odds ratio) in logistic regression models with age, calendar time, influenza season, and study site (random effect). Patients were stratified by prior season vaccination status in a subanalysis. Results Overall, 38% of patients (N = 6,558) were vaccinated in the current season, of whom 30% (N = 1,979) received LAIV4. Pooled VE of IIV against any influenza virus was 51% (95% CI: 47, 54) versus 26% (95% CI: 15, 36) for LAIV4. Point estimates for pooled VE against any influenza by age group ranged from 45% to 58% for IIV and 19% to 34% for LAIV4 during the 3 seasons (Figures 1 and 2). Pooled VE against influenza A(H1N1)pdm09 was 67% (95% CI: 62, 72) for IIV versus 20% (95% CI: −6, 39) for LAIV4. Pooled VE against influenza A(H3N2) was 29% (95% CI: 14, 42) for IIV versus 7% (95% CI: −11, 23) for LAIV4, and VE against influenza B was 52% (95% CI: 42, 60) for IIV and 66% (95% CI: 47, 77) for LAIV4. VE against influenza A(H1N1)pdm09 was lower for LAIV4 versus IIV across all strata of prior season vaccination (Figure 3). Conclusion Consistent with individual studies, our pooled analyses found that LAIV4 effectiveness was reduced for all age groups against influenza A(H1N1)pdm09 compared with IIV. This result did not vary based on prior vaccination status. Disclosures H. Caspard, AstraZeneca: Employee, Salary.

Influenza A H1N1 2009 Vaccine in Patients with Hematological Diseases: Good Safety and Immunogenicity Even in Heavily Chemotherapy-Treated Patients

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1054-1054
Author(s):  
Honar Cherif ◽  
Martin Hoglund ◽  
Karlis Pauksens
Keyword(s):  
Influenza Vaccine ◽  
Research Funding ◽  
Influenza A ◽  
Seasonal Influenza ◽  
Hematological Malignancies ◽  
World Health ◽  
Influenza B ◽  
Seasonal Influenza Vaccine ◽  
Hematological Diseases ◽  
Influenza A H1n1

Abstract Abstract 1054 Background: Patients with hematological malignancies are more susceptible for viral infections including influenza, which may be associated with prolonged illness, increased morbidity and mortality. In 2009, the World Health Organization classified the novel influenza A(H1N1) virus as pandemic. The impact of this viral infection in patients (pts) with hematological disorders was unknown, and there were concerns about the risk of serious complications. In Sweden, institutional guidelines recommended two doses of the AS03-adjuvanted inactivated H1N1 split vaccine Pandemrix™ from GlaxoSmithKline in these pts. Aims: Prospectively determine the safety, immunogenicity, and clinical efficacy of influenza A (H1N1) 2009 vaccination in patients with hematological diseases. Compare the immunological response to that obtained by the trivalent seasonal influenza vaccine (TIV). Patients and methods: 31 pts were included (myeloma 9, CLL 5, AML 6, ALL 2, CML 2, others 5), out of which 13 had undergone hematopoietic stem cell transplantation (HSCT). All received influenza A(H1N1) 2009 vaccine at day 0, and 28, and the majority (n=25) seasonal influenza vaccine at day 56. Serum for antibody analyses by validated HI-assays was taken at day 0, 28, 56 and 86 and at 1 year. The response to vaccination (seroconversion) was defined as at least a four-fold increase in antibody titer after vaccination or, in case prevaccination HI-titer was < 10, a post-vaccination titer of HI > 40 or greater. Considering that the HI-assay for influenza B differed from the A strains only the seroconversion rate was considered for the influenza B. Results: The A (H1N1) vaccine was well tolerated and no severe adverse events were reported. At day 28, a total of 16(52%) patients had protective levels of antibodies to A (H1N1) 2009 and 15(48%) had a seroconversion response. After the second dose of the vaccine, 25(81%) reached both protective levels of antibodies and seroconversion. At 1 year, protective levels of antibodies against A (H1N1) 2009 remained in 56% of responding patients. Seroconversion response was observed in 9/13 patients who had undergone HSCT, including 5/9 pts who had been transplanted within1–5 months, as well as in all (n=9) pts with myeloma having advanced disease and/or ongoing intense treatment. Following vaccination with TIV and evaluated at day 86, protective antibody levels and seroconversion response against A/Brisbane/59/2007 H1N1-like virus were detected in 10(40%) respective 7(28%), and against A/Uruguay/10/2007/H3N2-like virus in 14(56%) respective 10(40%). As for B/Brisbane/60/2008-like virus, seroconversion response was found in 5(20%) of all pts. Response to the pandemic influenza A (H1N1) 2009 vaccine was better than that to the three TIV strains (p<0.001, p<0.009 and p<0.001 respectively). Conclusion: A substantial proportion of patients with hematological malignancies including even heavily treated Myeloma and HSCT patients mounted a good response to the adjuvanted influenza A (H1N1) 2009 vaccine. This vaccine was well tolerated and had a significantly better immunogenicity than that of the non-adjuvanted seasonal influenza vaccine. Disclosures: Cherif: GSK: Research Funding. Pauksens:GSK: Research Funding.

scholarly journals Circulating influenza viruses and the effectiveness of seasonal influenza vaccine in Romania, season 2012-2013 / Virusurile gripale circulante și eficacitatea vaccinului gripal sezonier în România, în sezonul 2012-2013

2015 ◽  
Vol 23 (1) ◽  
Author(s):  
Daniela Pitigoi ◽  
George Necula ◽  
Viorel Alexandrescu ◽  
Maria Elena Mihai ◽  
Carmen Maria Cherciu ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Vaccine Strain ◽  
Influenza A ◽  
Seasonal Influenza ◽  
Influenza Viruses ◽  
Nucleotide Sequencing ◽  
Influenza B ◽  
Seasonal Influenza Vaccine ◽  
Negative Case ◽  
Influenza A H1n1

AbstractBackgound. Using influenza epidemiological and virological surveillance data, we aimed at investigating the profile of influenza viruses circulating in Romania during the season 2012-2013 and estimating the effectiveness (VE) of the seasonal vaccine. Methods. We tested all specimens collected from patients with influenza like illness (ILI) in the national surveillance system between week 40/2012 to week 20/2013. Influenza A/B positive specimens identified by molecular detection (RT-PCR) were further characterized. We used hemagglutination inhibition assay for antigenic characterization and chemiluminiscence assay for the antiviral susceptibility testing. Subsequently we conducted nucleotide sequencing of hemagglutinin and neuraminidase genes and phylogenetic tree analyses. We estimated influenza VE using the test negative case-control study design, as 1-odds ratio of vaccination among ILI cases positive for influenza and ILI negative controls. Results and Discussions. We tested 1087 specimens, and 537 cases were positive (56.2% influenza B, 40.6% A(H1N1)pdm09, 3.2% A(H3N2). Sixty-four influenza viruses were antigenically and/or genetically characterized. A(H1N1)pdm09 viruses were related to the vaccine strain A/ California/07/2009 and clustered with genetic group 6 similar to A/St. Petersburg/27/2011. Influenza B viruses belonged to clade 2 of type B/Yamagata lineage, related to B/Estonia/55669/2011 except one, B/Victoria lineage, representative strain B/Brisbane/60/2008. A(H3) viruses clustered with group 3C of the A/Victoria/208/2009 clade, similar to the vaccine strain A/Victoria/361/2011. All tested strains (57) demonstrated susceptibility to oseltamivir and zanamivir. The adjusted seasonal influenza vaccine effectiveness against influenza A(H1N1)pdm09 (N=119) was 76.9% (95% CI: -113.4, 98.5), suggesting a good protection, consistent with the good match between the vaccine and circulating strains.

scholarly journals Interim 2019/20 influenza vaccine effectiveness: six European studies, September 2019 to January 2020

2020 ◽  
Vol 25 (10) ◽  
Author(s):  
Angela Rose ◽  
Esther Kissling ◽  
Hanne-Dorthe Emborg ◽  
Amparo Larrauri ◽  
Jim McMenamin ◽  
...  
Keyword(s):  
Primary Care ◽  
Influenza Vaccine ◽  
Influenza A ◽  
Age Groups ◽  
Vaccine Effectiveness ◽  
Influenza B ◽  
European Studies ◽  
Case Definitions ◽  
Point Estimates ◽  
Influenza A H1n1

Background Influenza A(H1N1)pdm09, A(H3N2) and B viruses were co-circulating in Europe between September 2019 and January 2020. Aim To provide interim 2019/20 influenza vaccine effectiveness (VE) estimates from six European studies, covering 10 countries and both primary care and hospital settings. Methods All studies used the test-negative design, although there were some differences in other study characteristics, e.g. patient selection, data sources, case definitions and included age groups. Overall and influenza (sub)type-specific VE was estimated for each study using logistic regression adjusted for potential confounders. Results There were 31,537 patients recruited across the six studies, of which 5,300 (17%) were cases with 5,310 infections. Most of these (4,466; 84%) were influenza A. The VE point estimates for all ages were 29% to 61% against any influenza in the primary care setting and 35% to 60% in hospitalised older adults (aged 65 years and over). The VE point estimates against A(H1N1)pdm09 (all ages, both settings) was 48% to 75%, and against A(H3N2) ranged from −58% to 57% (primary care) and −16% to 60% (hospital). Against influenza B, VE for all ages was 62% to 83% (primary care only). Conclusions Influenza vaccination is of continued benefit during the ongoing 2019/20 influenza season. Robust end-of-season VE estimates and genetic virus characterisation results may help understand the variability in influenza (sub)type-specific results across studies.

scholarly journals Prevention of Influenza Hospitalization Among Adults in the United States, 2015–2016: Results From the US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN)

2018 ◽  
Vol 220 (8) ◽  
pp. 1265-1275 ◽  
Author(s):  
Jill M Ferdinands ◽  
Manjusha Gaglani ◽  
Emily T Martin ◽  
Don Middleton ◽  
Arnold S Monto ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Influenza A ◽  
The United States ◽  
Vaccine Effectiveness ◽  
Severe Illness ◽  
Influenza B Virus ◽  
Influenza B ◽  
Negative Case ◽  
Influenza A H1n1 ◽  
The Us

Abstract Background Evidence establishing effectiveness of influenza vaccination for prevention of severe illness is limited. The US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) is a multiyear test-negative case-control study initiated in 2015–2016 to estimate effectiveness of vaccine in preventing influenza hospitalization among adults. Methods Adults aged ≥18 years admitted to 8 US hospitals with acute respiratory illness and testing positive for influenza by polymerase chain reaction were cases; those testing negative were controls. Vaccine effectiveness was estimated with logistic regression adjusting for age, comorbidities, and other confounding factors and stratified by frailty, 2-year vaccination history, and clinical presentation. Results We analyzed data from 236 cases and 1231 controls; mean age was 58 years. More than 90% of patients had ≥1 comorbidity elevating risk of influenza complications. Fifty percent of cases and 70% of controls were vaccinated. Vaccination was 51% (95% confidence interval [CI], 29%–65%) and 53% (95% CI, 11%–76%) effective in preventing hospitalization due to influenza A(H1N1)pdm09 and influenza B virus infection, respectively. Vaccine was protective for all age groups. Conclusions During the 2015–2016 US influenza A(H1N1)pdm09–predominant season, we found that vaccination halved the risk of influenza-association hospitalization among adults, most of whom were at increased risk of serious influenza complications due to comorbidity or age.

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