Using surveillance data to estimate pandemic vaccine effectiveness against laboratory confirmed influenza A(H1N1)2009 infection: two case-control studies, Spain, season 2009-2010
1 Institute of Health Carlos III, National Centre of Epidemiology, c/Monforte de Lemos no.5, 28029 Madrid, Spain
2 EpiConcept, 47, rue de Charenton 75012 Paris, France
3 Institute of Health Carlos III, National Centre for Microbiology, National Influenza Centre, 28220 Majadahonda, Madrid, Spain
4 Service of Epidemiology, General Directorate of Public Health, Baleares, c/Cecilio Metelo 18. 07003 Palma de Mallorca, Spain
5 Dirección General de Salud Pública e Investigación, Desarrollo e Innovación. Consejería de Sanidad de Castilla y León, Paseo Zorrilla 1, 47071 Valladolid, Spain
6 Department of Health, Generalitat of Catalonia, C/Roc Boronat 81-95, 08005 Barcelona, Spain
7 Sub-directorate of Epidemiology, Public Health Directorate, Avda América 2, 06800 Mérida, Badajoz, Spain
8 Institute of Public Health of Navarra, Leyre 15, 31003 Pamplona, Spain
9 Sub-directorate of Public Health, Gipuzkoa, Avda Navarra 4, 20013 Donostia-San Sebastián, Spain
10 Public Health Service, Department of Health, Basque Government, C/Donostia-San Sebastian 1, 01010, Vitoria-Gasteiz, Spain
11 General Directorate of Public Health and Consumption, Consejería de Salud. La Rioja Government, C/Gran Vía del rey D. Juan Carlos, no 18, 26071 Logroño, Spain
12 Consortium for Biomedical Research in Epidemiology & Public Health, Institute of Health Carlos III, Spain
BMC Public Health 2011, 11:899 doi:10.1186/1471-2458-11-899Published: 30 November 2011
Physicians of the Spanish Influenza Sentinel Surveillance System report and systematically swab patients attended to their practices for influenza-like illness (ILI). Within the surveillance system, some Spanish regions also participated in an observational study aiming at estimating influenza vaccine effectiveness (cycEVA study). During the season 2009-2010, we estimated pandemic influenza vaccine effectiveness using both the influenza surveillance data and the cycEVA study.
We conducted two case-control studies using the test-negative design, between weeks 48/2009 and 8/2010 of the pandemic season. The surveillance-based study included all swabbed patients in the sentinel surveillance system. The cycEVA study included swabbed patients from seven Spanish regions. Cases were laboratory-confirmed pandemic influenza A(H1N1)2009. Controls were ILI patients testing negative for any type of influenza. Variables collected in both studies included demographic data, vaccination status, laboratory results, chronic conditions, and pregnancy. Additionally, cycEVA questionnaire collected data on previous influenza vaccination, smoking, functional status, hospitalisations, visits to the general practitioners, and obesity. We used logistic regression to calculate adjusted odds ratios (OR), computing pandemic influenza vaccine effectiveness as (1-OR)*100.
We included 331 cases and 995 controls in the surveillance-based study and 85 cases and 351 controls in the cycEVA study. We detected nine (2.7%) and two (2.4%) vaccine failures in the surveillance-based and cycEVA studies, respectively. Adjusting for variables collected in surveillance database and swabbing month, pandemic influenza vaccine effectiveness was 62% (95% confidence interval (CI): -5; 87). The cycEVA vaccine effectiveness was 64% (95%CI: -225; 96) when adjusting for common variables with the surveillance system and 75% (95%CI: -293; 98) adjusting for all variables collected.
Point estimates of the pandemic influenza vaccine effectiveness suggested a protective effect of the pandemic vaccine against laboratory-confirmed influenza A(H1N1)2009 in the season 2009-2010. Both studies were limited by the low vaccine coverage and the late start of the vaccination campaign. Routine influenza surveillance provides reliable estimates and could be used for influenza vaccine effectiveness studies in future seasons taken into account the surveillance system limitations.