Role of influenza vaccine in pneumococcal pneumonia using the Screening Method: a pilot study

Rodrigues, Ana Paula; Kislaya, Irina; Machado, Ausenda; Gómez, Verónica; Bárbara, Cristina; Gonçalves, Paulo; Nunes, Baltazar

http://hdl.handle.net/10400.18/6010

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Background: Influenza viruses can induce pneumonia and also favour bacterial co-infections and secondary bacterial infections and pneumococci exhibit a special synergism with influenza and other respiratory viruses. As consequence, there is plausibility that influenza vaccination may also protect against pneumococcal outcomes. The aim of this pilot study was to estimate the influenza vaccine effectiveness against hospitalized pneumococcal pneumonia (PP) using the screening method. Methods: A pilot study using the screening method was set up between week 40/2014 and week 22/2016, using as cases PP (lab confirmed) admitted in one central hospital in Lisbon. A sample of households of Lisbon region that participated in a telephone interview was used as reference population. Cases were considered vaccinated against influenza if they had registry of seasonal influenza vaccine until 14 before the hospitalization. Influenza vaccine coverage (IVC) within the reference population was estimated by telephone interview. Results: 162 pneumonia cases were enrolled, 45 were excluded (nosocomial infection, co-infection, occurred out of influenza circulation period, living out of study area). Of the 117 selected cases, 24 had PP. Differences on IVC were found between PP (29.2%), pneumonia with no identified agent (46.2%) and reference population (52.3%). Crude influenza vaccine effectiveness against hospitalized pneumococcal pneumonia was 62.4% (IC95: 17.4%; 85.9%). Considering that vaccine coverage in cases could be underestimated, as 32 % people aged 65 and more living in Lisbon region was vaccinated out of the National Health System, we maximized the vaccine coverage in cases according this hypothesis until 42.9%, and thus the vaccine effectiveness decreased to 42.3% (IC95: -30.1%; 74.6%). Discussion: IVE was higher than reported in Japan (31.7%; CI: 0.6%; 53.1%), but with overlapping confidence intervals. Regarding the IVE against severe Influenza cases observed in 2015/16 in Europe and Portugal, we considered that our IVE against PP is probably overestimated. However, it may indicate some level of protection of the influenza vaccine against PP. Besides the limitations of screening method, given the improvement in data quality and the perspective of using alternative reference populations we consider this study design feasible to rapidly access the IVE against PP.