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DDI - Relatórios científicos e técnicos

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Browsing DDI - Relatórios científicos e técnicos by Author "Batista, Inês"

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  • Case control study for measuring influenza vaccine effectiveness in Portugal - Season 2010-11- Final report
    Publication . Nunes, Baltazar; Pechirra, Pedro; Machado, Ausenda; Falcão, Isabel; Gonçalves, Paulo; Conde, Patricia; Batista, Inês; Guiomar, Raquel; Marinho Falcão, José
    Every year, influenza virus is responsible for epidemics that affect human health causing respiratory infections that could lead to serious health complications of individuals belonging to risk groups, as well as on the functioning of health services. In order to mitigate influenza impacts, vaccination has been one of the main measures, being recognized its role in reducing the risk of developing the disease and the occurrence of their complications. Thus, since the vaccine is reformulated every season estimating the influenza vaccine effectiveness (VE) every season and in an early stage is of major importance to support public health decisions. Since 2008-2009, Portugal has been participating in I-MOVE project that aims to estimate seasonal and pandemic vaccine effectiveness during and after the influenza season. Last season, 2010-2011, Portugal once again joined the I-MOVE multi-center case control study (with the national VE study- Euroeva) together with Spain, Ireland, France, Italy, Romania, Hungary and Poland, using a common protocol and with the objective of estimate the 2010-11 seasonal influenza vaccine effectiveness respectively in the elderly (65+) and in all age groups. Additionally, using information on 2010-11 seasonal vaccine coverage in the population, it has been also proposed to estimate 2010-11 seasonal vaccine effectiveness using the screening method. Material and Methods Two different approaches were used so as to estimate vaccine effectiveness: a) For the test negative design (TND), a case-control approach was used, where laboratory confirmed influenza cases (ILI+) were compared to laboratory negative influenza ILI patients (ILI-). On a weekly basis, each GP selected systematically ILI patients (two per week from all ages and all ILI patients with 65 years and more) using the EU ILI case definition. Data on confounding factors and effect modifiers was collected using a standardized questionnaire. VE was estimated as one minus the odds ratio of being vaccinated in cases versus controls adjusted for confounders by logistic regression. b) For the screening method, the 2010-11 seasonal vaccine coverage was compared between a sample of ILI cases and a sample of ILI cases laboratory confirmed for influenza with the vaccine coverage estimated in the general population. ILI cases and ILI Positive cases were the same as the one used in the TND. Vaccine coverage in the population was obtained from a sample of 1074 households stratified by region (homogeneous allocation) selected from a dual sample frame – random digit dialing mobile and landline phones (ECOS sample). The relevant information was collected by CATI (Computer Assisted Telephone interview) with the same questionnaire – one respondent by household (proxy for the rest of the household members). VE was estimated by comparing the proportion of cases vaccinated to the vaccine coverage in the source population using the Orenstein formula and the Farrington method to adjust for confounders. For both methods an ILI patient was considered vaccinated if he/she had received one dose of the vaccine at least 14 days prior onset of symptoms. Data analysis comprised ILI positive cases selected between week 45 of 2010 and week 11 of 2011. Results In Portugal, the 2010-2011 influenza season was characterized by a mixed circulation of influenza virus. In the early beginning of the season, B type virus dominated the season, until week 1 where A(H1N1)2009 virus started to dominate. Also in circulation, but in a minor proportion was the A(H3) virus. a) Test negative design results: Considering TND results, 58 GP’s accepted to participate in the study, with 60% participation rate (35 GP’s effectively participated in the study by selecting patients). Excluding 33 ILI cases (for not meeting the inclusion criteria) the final sample for analyses consisted on 253 ILI patients with a high positive rate (57%). Among cases, 73 were positive for B virus, 69 for A(H1N1)2009 and 2 for A(H3). For analysis purposes three groups of cases were defined: All influenza, Influenza B and Influenza A(H1N1)2009 that were compared to ILI cases that tested negative for influenza virus (109 Controls). After adjustment for age group, pandemic and seasonal vaccine 2009-10 season, any chronic disease, target group, GP visits and month of onset, VE point estimates were: • 58% (CI95% -61 – 89) for All influenza • 34% (CI95% -98 – 97) for Influenza A(H1N1)2009 and • 75% (CI95% -255 – 88) for Influenza B. Nevertheless, no statistical significance was obtained for either the analysis. b) Screening method results In season 2010-2011, 903 households of the ECOS-sample were interviewed (which corresponds to 2684 individuals). The final estimated vaccine coverage was 17.5% (CI95% 15.1-20.3), with a gradient evolution since September 2010 (3.5%) till December 2010 (16.6%). Crude and adjusted VE (using the Farrington method) estimates were computed for medically attended ILI cases and ILI influenza positive cases. Overall results indicate that after adjustment for confounding (age group and presence of chronic diseases), VE point estimates decreased from 47.0% to 33.3% in ILI cases and from 70.1% to 63.7% in ILI positive cases. Due to the small sample size, no VE estimates were computed for the individuals of the vaccination target group, i.e., individuals with 65 years and more and the ones with at least one chronic disease. Conclusions Overall results obtained by the Euroeva study indicate that crude 2010-11 seasonal VE estimate against medically attended influenza was 79% (CI95% 43-94) and 70% (CI95% 32-87), respectively for the TND and screening method. After adjustment the respective VE estimates decreased: 58 (CI95% -61-89) and 64% (CI95% 17-84). These results were in accordance to the up to now published results (42-65%). The TND study was also able to provide strain specific 2010-11 seasonal VE estimates: influenza B, crude VE=87% (CI95% 41-99) and adjusted VE=75% (CI95% -98-97) and for influenza A(H1N1)2009, crude VE=74% (CI95% 14-94) and adjusted VE=34% (CI95% -254-88). These results suggest that the 2010-11 seasonal VE was lower than the monovalent A(H1N1)2009 VE estimated by the IMOVE multicenter study in the season 2009-10: 72% (CI95% 46-86). Our study was unable to estimate VE for specific seasonal vaccine target groups. This result enhances, as in previous studies, the unavoidable need for pooling data from network of VE studies with common protocol as IMOVE. Recommendations The main recommendations focused on: • To calculate sample size taking into consideration: o the context of the multicentre case-control study: minimum sample size per site in order to assure a minimum homogeneity for pooled analysis; o different expected VE point estimates, i.e. for low, medium and high VE; o minimum set of factors for stratified analysis; o the adjustment for confounders. • To increase sample size, mainly in the elderly population (aged 65 years or more); • To increase the total number of participating GP’s in the study by exploring other sources of GP’s recruitment; • To study the inclusion of the population based vaccine coverage uncertainty in the screening method; • To explore with participating GP’s the best way to obtain estimates of the Euroeva ILI sample fraction. Finally we also recommend continuing the harmonization of the study designs between participating countries with the multi-centre study objective.
    2011-06-01Report Open access Show more
  • Influenza Vaccine Effectiveness in Portugal: Season 2011-12. Final Report
    Publication . Nunes, Baltazar; Guiomar, Raquel; Machado, Ausenda; Pechirra, Pedro; Gonçalves, Paulo; Conde, Patrícia; Batista, Inês; João, Inês; Falcão, Isabel
    The EuroEVA project is the Portuguese component of the multicentre I-MOVE study and aims to obtain estimates of the seasonal and pandemic vaccine effectiveness during and after the influenza season. Since the 2008/2009 influenza season Portugal, along with other European countries, has implemented a common protocol using a case-control study design, where influenza-like illness cases which are laboratory confirmed as influenza (ILI+) are compared to a control group consisting of ILI patients which test negative for influenza (ILI-) (Case-control Test negative design). The results presented in this report relate to the EuroEVA 2011-2012 season and aim to estimate the seasonal influenza vaccine effectiveness for the age group 60+ years and in all age groups, using two approaches: Case-control Test negative design and Screening Method. Materials and Methods Test Negative Design ILI cases were identified among patients that presented ILI symptoms to a participating EuroEVA General Medical Practitioner (GP). On a weekly basis, each GP systematically selected ILI patients (two per week with less than 60 years and all ILI patients with 60 years and more) using the EU ILI case definition. Data on potential confounding factors and effect modifiers was collected using a standardized questionnaire which included information on socio-demographic variables (age, gender, education and co-inhabitants), previous (2010-11) influenza vaccination, chronic conditions and related hospitalizations, current smoking habits, belonging to GP list and number of consultations in the previous year. An ILI patient was considered vaccinated if he/she had received one dose of the 2011/2012 trivalent influenza vaccine at least 14 days prior to onset of symptoms. VE was estimated as one minus the odds ratio of being vaccinated in cases versus controls adjusted for confounders by logistic regression. Potential confounders were investigated and included if: they changed crude OR estimate in at least 10% after adjustment by the Mantel-Haenszel method, were associated both to being a case (in the absence of the exposure factor) and to the seasonal vaccination. Screening Method ILI cases and ILI laboratory confirmed influenza cases were recruited in the context of the National I-MOVE case-control study (EuroEVA). Vaccine coverage in the population was obtained from a sample of 1074 households stratified by region (homogeneous allocation) selected from a dual sample frame: random digit dialling mobile and landline phones (ECOS sample). Relevant information was collected by CATI (Computer Assisted Telephone interview) – one respondent by household (proxy for the rest of the household members). VE was estimated by comparing the proportion of vaccinated cases to the vaccine coverage in the source population, using the Orenstein formula and the Farrington method to adjust for age group and target group for vaccination. Results In Portugal, a later beginning of the 2011/2012 influenza epidemic was observed, starting in week 4/2012 and ending at week 12/2012. In this season both influenza B and A(H3) virus types were circulating, with predominance of the later. Test negative design From the 59 GP’s that accepted to participate in the study, 35 effectively participated in the study by selecting patients (which corresponds to a 59% participation rate). After excluding 79 ILI cases (for not adhering to the inclusion criteria) the final sample consisted on 273 ILI patients. Of the 134 cases which tested positive for influenza, 98.5% were positive for influenza A(H3) and the remaining for type B virus. The control group, consisting of 139 ILI patients who tested negative for influenza, was statistically different (p<0.05) from the ILI+ group in the following variables: • Clinical signs and symptoms: cough (higher in cases than in controls: 95.5% vs. 89.2%, respectively) and sore throat (more frequent in controls, 89.2%, than in cases ,75.4%); • Age: controls were older than cases (median age in controls was 52 yrs vs. 39 yrs in cases); • Any chronic disease: the prevalence of at least one chronic condition relevant for influenza vaccination was higher in controls (41.7% vs 29.1%); • Seasonal vaccine in 2010-11: controls were more often vaccinated against influenza in the last season than cases (30.2% vs. 14.4%); • Co-habitants: the median number of co-habitants was higher in cases (3 vs. 2). Considering all population, vaccine coverage (VC) in controls was 27.5% statistically higher than in cases (VC=13.4%). Similar results were obtained for the sub-group target for vaccination by the National Health Authorities (VC cases =24.6% and VC controls=46.1%, p=0.010). These results indicate that crude VE estimates was 59.2% (95% CI: 21.1%-79.4%) in the general population and 61.8% (95% CI: 15.5% ;83.1%) in the target group for vaccination. After adjustment for co-inhabitants and month of onset of illness, VE adjusted estimates were 48.8% (95% CI: 0.0% ; 73.8%) and 51.6% (95% CI:-6.2%-77.9%) for the general population and for the target group, respectively. Screening Method The ECOS telephone survey was conducted during April 2012, and information was obtained from a total of 2395 individuals. According to the results, individuals were vaccinated from October 2011 through January 2012, estimating a 16.4% (95% CI: 13.6-19.6) vaccine coverage (VC) in the population. In the 60+ yrs age group, the VC was 37.3% (95% CI: 30.6-44.4) and for the individuals with chronic condition was 28.0% (95% CI: 23.0-33.7). The crude VE estimated with the Screening method for ILI+ as the outcome was 27.0% (95% CI: -19.9- 55.6) and -32.4% (95% CI: -77.7- 1.3) for ILI. Adjusted VE estimates varied from -90.4% (95% CI: -277.1- 3.9) (60+ yrs) to 6.1% (95% CI: -56.0- 43.4) (0-60 yrs) considering ILI as the outcome and from -58.6% (95% CI: -195.3- 14.8) to 56.9 (95% CI: -35.2- 86.3) for ILI positive outcomes (none were statistically significant). Conclusions Given the 3 years experience in conducting this study, logistical and implementation aspects were straightforward. The 2011-2012 season adjusted VE estimates were similar for the general population (48.8%) and for the target group (51.6%), although not statistical significant. When compared to the previous season, VE point estimate for the general population was lower (VE=58% in 2010-11), although the CI overlap. The population studied this year was older than in the last season. The time between onset of symptoms and swabbing, was also different with marginally, non significant, differences between cases and controls.
    2012-08Report Open access Show more