Autor(es): Gómez, Verónica ; Guiomar, Raquel ; Rodrigues, Ana Paula ; Pechirra, Pedro ; Conde, Patrícia ; Cristóvão, Paula ; Costa, Inês ; Nunes, Baltazar ; Machado, Ausenda
Data: 2016
Identificador Persistente: http://hdl.handle.net/10400.18/4015
Origem: Repositório Científico do Instituto Nacional de Saúde
Assunto(s): Gripe; Vacina Antigripal; Efetividade da Vacina; Cuidados de Saúde; Infecções Respiratórias; Época 2015/2016; Saúde Pública; Portugal; Influenza Vaccine; Effectiveness
The results to be presented are related to the 8th EuroEVA season (the Portuguese component of the multicentre I-MOVE study) and aimed the estimation of 2015/2016 end of season influenza vaccine effectiveness in i) all age groups and in <65 and 65 plus years ; ii) by risk group; iii) by influenza subtype and clade. Material and methods: The “Protocol for case-control studies to measure seasonal influenza vaccine effectiveness in the European Union and European Economic Area Member States- Portuguese site study version” was implemented entirely adding a new variable related to statin uptake. Also, a pilot study to incorporate genetic characterization of influenza virus from patients enrolled in vaccine effectiveness (VE) study was implemented. Within this pilot study, influenza A(H1)pdm09 positive cases were randomly selected to be genetically characterized. Selection was conducted in three phases of the epidemic: early, peak and late season. Results: In Portugal, a low intensity influenza epidemic occurred between week 53/2015 and week 8/2016. Influenza A(H1)pdm09 virus predominated during all season. Influenza B/Victoria lineage was detected in co-circulation in late season. From the 84 GP’s that accepted to participate in the study, 51 GP’s effectively participated in the study selecting patients (60.7% participation rate). A total of 336 ILI patients were enrolled and after excluding 26 ILI patients the final sample for analyses consisted on 310 ILI patients (147 cases and 102 controls). From the cases, 89.5% were positive for influenza A(H1)pdm09, 8.9% were positive for influenza B/Victoria and the remaining (1.6%) were positive for influenza A(H3). For genetic characterization of influenza virus, A(H1)pdm09 virus subtype was selected. The HA1 subunit of the hemaglutinin gene were successfully sequenced for 93 out of 126 cases with detected viruses. Phylogenetic analysis and clade assignment were performed. The majority of A(H1)pdm09 viruses belonged to the subgroup 6B.1 (87.1%) and the remaining viruses belonged to 6B clade. Comparing cases and controls, was confirmed that they were statistically different in relation to time between onset and swab collection, sex, seasonal vaccine uptake in 2014/2015, presence of at least one chronic disease and number of GP consultations in last 12 months. For 2015/2016 trivalent influenza vaccine, confounder- adjusted VE against A(H1)pdm09 was 54.0% (95% CI: -1.5; 79.2%) in all population and 63.9% (95% CI: (7.7%; 85.9%) in the target group for vaccination. Considering the population with less than 65 years, VE against AH1pdm09 was 56.2% (95% CI: -17.5%; 83.7%) and 74.9% (95% CI: -37.1; 95.4%) in the and more years of age. Conclusions: VE estimates during 2015/2016 season indicated that the seasonal flu vaccine conferred moderate protection against A(H1)pdm09 (varied between 54% to 64% considering all population and the target group for vaccination). The vaccine had a better performance in the elderly, where VE point estimates reached 75% (not significant nevertheless). The implementation of the genetic characterization pilot study was well succeeded, with a success rate of influenza virus characterization of 80.2%. For future seasons, the high sampling fraction in the first phase should continue in order to assist the definition of the virus subtype/clade target during the season.
