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      Prospective hospital-based case–control study to assess the effectiveness of pandemic influenza A(H1N1)pdm09 vaccination and risk factors for hospitalization in 2009–2010 using matched hospital and test-negative controls

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          Abstract

          Background

          We performed a case–control study to estimate vaccine effectiveness (VE) for prevention of hospitalization due to pandemic influenza A(H1N1)pdm09 (pH1N1) and to identify risk factors for pH1N1 and acute respiratory infection (ARI) in 10 hospitals in Berlin from December 2009 to April 2010.

          Methods

          Cases were patients aged 18–65 years with onset of ARI ≤10 days before admission testing positive for pH1N1 by PCR performed on nasal and throat swabs or by serological testing. Cases were compared to (1) matched hospital controls with acute surgical, traumatological or other diagnoses matched on age, sex and vaccination probability, and (2) ARI patients testing negative for pH1N1. Additionally, ARI cases were compared to matched hospital controls. A standardized interview and chart review elicited demographic and clinical data as well as potential risk factors for pH1N1/ARI. VE was estimated by 1-(Odds ratio) for pH1N1-vaccination ≥10 days before symptom onset using exact logistic regression analysis.

          Results

          Of 177 ARI cases recruited, 27 tested pH1N1 positive. A monovalent AS03-adjuvanted pH1N1 vaccine was the only pandemic vaccine type identified among cases and controls (vaccination coverage in control group 1 and 2: 15% and 5.9%). The only breakthrough infections were observed in 2 of 3 vaccinated HIV positive pH1N1 patients. After exclusion of HIV positive participants, VE was 96% (95%CI: 26-100%) in the matched multivariate analysis and 46% (95%CI: -376-100%) in the test-negative analysis. Exposure to children in the household was independently associated with hospitalization for pH1N1 and ARI.

          Conclusions

          Though limited by low vaccination coverage and number of pH1N1 cases, our results suggest a protective effect of the AS03-adjuvanted pH1N1 vaccine for the prevention of pH1N1 hospitalization. The use of hospital but not test-negative controls showed a statistically protective effect of pH1N1-vaccination and permitted the integrated assessment of risk factors for pH1N1-infection. To increase statistical power and to permit stratified analyses (e.g. VE for specific risk groups), the authors suggest pooling of future studies assessing effectiveness of influenza vaccines for prevention of severe disease from different centres.

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          Most cited references45

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          Pneumonia and respiratory failure from swine-origin influenza A (H1N1) in Mexico.

          In late March 2009, an outbreak of a respiratory illness later proved to be caused by novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in Mexico. We describe the clinical and epidemiologic characteristics of persons hospitalized for pneumonia at the national tertiary hospital for respiratory illnesses in Mexico City who had laboratory-confirmed S-OIV infection, also known as swine flu. We used retrospective medical chart reviews to collect data on the hospitalized patients. S-OIV infection was confirmed in specimens with the use of a real-time reverse-transcriptase-polymerase-chain-reaction assay. From March 24 through April 24, 2009, a total of 18 cases of pneumonia and confirmed S-OIV infection were identified among 98 patients hospitalized for acute respiratory illness at the National Institute of Respiratory Diseases in Mexico City. More than half of the 18 case patients were between 13 and 47 years of age, and only 8 had preexisting medical conditions. For 16 of the 18 patients, this was the first hospitalization for their illness; the other 2 patients were referred from other hospitals. All patients had fever, cough, dyspnea or respiratory distress, increased serum lactate dehydrogenase levels, and bilateral patchy pneumonia. Other common findings were an increased creatine kinase level (in 62% of patients) and lymphopenia (in 61%). Twelve patients required mechanical ventilation, and seven died. Within 7 days after contact with the initial case patients, a mild or moderate influenza-like illness developed in 22 health care workers; they were treated with oseltamivir, and none were hospitalized. S-OIV infection can cause severe illness, the acute respiratory distress syndrome, and death in previously healthy persons who are young to middle-aged. None of the secondary infections among health care workers were severe. 2009 Massachusetts Medical Society
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            Detection of antibody to avian influenza A (H5N1) virus in human serum by using a combination of serologic assays.

            From May to December 1997, 18 cases of mild to severe respiratory illness caused by avian influenza A (H5N1) viruses were identified in Hong Kong. The emergence of an avian virus in the human population prompted an epidemiological investigation to determine the extent of human-to-human transmission of the virus and risk factors associated with infection. The hemagglutination inhibition (HI) assay, the standard method for serologic detection of influenza virus infection in humans, has been shown to be less sensitive for the detection of antibodies induced by avian influenza viruses. Therefore, we developed a more sensitive microneutralization assay to detect antibodies to avian influenza in humans. Direct comparison of an HI assay and the microneutralization assay demonstrated that the latter was substantially more sensitive in detecting human antibodies to H5N1 virus in infected individuals. An H5-specific indirect enzyme-linked immunosorbent assay (ELISA) was also established to test children's sera. The sensitivity and specificity of the microneutralization assay were compared with those of an H5-specific indirect ELISA. When combined with a confirmatory H5-specific Western blot test, the specificities of both assays were improved. Maximum sensitivity (80%) and specificity (96%) for the detection of anti-H5 antibody in adults aged 18 to 59 years were achieved by using the microneutralization assay combined with Western blotting. Maximum sensitivity (100%) and specificity (100%) in detecting anti-H5 antibody in sera obtained from children less than 15 years of age were achieved by using ELISA combined with Western blotting. This new test algorithm is being used for the seroepidemiologic investigations of the avian H5N1 influenza outbreak.
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              Viral Loads and Duration of Viral Shedding in Adult Patients Hospitalized with Influenza

              Abstract BackgroundThe goal of this study was to characterize viral loads and factors affecting viral clearance in persons with severe influenza MethodsThis was a 1-year prospective, observational study involving consecutive adults hospitalized with influenza. Nasal and throat swabs were collected at presentation, then daily until 1 week after symptom onset. Real-time reverse-transcriptase polymerase chain reaction to determine viral RNA concentration and virus isolation were performed. Viral RNA concentration was analyzed using multiple linear or logistic regressions or mixed-effect models ResultsOne hundred forty-seven inpatients with influenza A (H3N2) infection were studied (mean age ± standard deviation, 72±16 years). Viral RNA concentration at presentation positively correlated with symptom scores and was significantly higher than that among time-matched outpatients (control subjects). Patients with major comorbidities had high viral RNA concentration even when presenting >2 days after symptom onset (mean ± standard deviation, 5.06±1.85 vs 3.62±2.13 log10 copies/mL; P=.005; β, +0.86 [95% confidence interval, +0.03 to +1.68]). Viral RNA concentration demonstrated a nonlinear decrease with time; 26% of oseltamivir-treated and 57% of untreated patients had RNA detected at 1 week after symptom onset. Oseltamivir started on or before symptom day 4 was independently associated with an accelerated decrease in viral RNA concentration (mean β [standard error], −1.19 [0.43] and −0.68 [0.33] log10 copies/mL for patients treated on day 1 and days 2–3, respectively; P<.05) and viral RNA clearance at 1 week (odds ratio, 0.10 [95% confidence interval, 0.03–0.35] and 0.30 [0.10–0.90] for patients treated on day 1–2 and day 3–4, respectively). Conversely, major comorbidities and systemic corticosteroid use for asthma or chronic obstructive pulmonary disease exacerbations were associated with slower viral clearance. Viral RNA clearance was associated with a shorter hospital stay (7.0 vs 13.5 days; P=.001) ConclusionPatients hospitalized with severe influenza have more active and prolonged viral replication. Weakened host defenses slow viral clearance, whereas antivirals started within the first 4 days of illness enhance viral clearance
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                Author and article information

                Journal
                BMC Infect Dis
                BMC Infect. Dis
                BMC Infectious Diseases
                BioMed Central
                1471-2334
                2012
                31 May 2012
                : 12
                : 127
                Affiliations
                [1 ]Immunization Unit, Department of Infectious Disease Epidemiology, Robert Koch Institute, DGZ-Ring 1, 13086 Berlin, Germany
                [2 ]National Reference Centre for Influenza, Robert Koch Institute, Berlin, Germany
                [3 ]Post Graduate Training in Applied Epidemiology, Robert Koch Institute, Berlin, Germany
                [4 ]Department of Infectious Diseases, Vivantes Auguste-Viktoria Klinik, Berlin, Germany
                Article
                1471-2334-12-127
                10.1186/1471-2334-12-127
                3464893
                22650369
                30568143-a51a-4e9c-82f9-39cb30a48ab0
                Copyright ©2012 Hellenbrand et al.; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 28 September 2011
                : 31 May 2012
                Categories
                Research Article

                Infectious disease & Microbiology
                risk factors,influenza,h1n1,case–control study,vaccine effectiveness,hospitalization

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