Effectiveness of 23-valent pneumococcal polysaccharide vaccine in adults aged 60 years and over in the Region of Madrid, Spain, 2008–2011 
Gutiérrez Rodríguez, M A and Ordobás Gavín, M A and García-Comas, L and Sanz Moreno, J C and Córdoba Deorador, E and Lasheras Carbajo, M D and Taveira Jiménez, J A and Martín Martínez, F and Iniesta Fornies, D and Arce Arnaez, A, Eurosurveillance, 19, 20922 (2014), https://doi.org/10.2807/1560-7917.ES2014.19.40.20922