1. Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
2. Department of Medical Biotechnologies, University of Siena, Siena, Italy
3. Department of Biomedical Sciences and Public Health, Polytechnic University of Marche Medical School, Ancona, Italy
4. Research Centre, GlaxoSmithKline Vaccines S.r.l, Siena, Italy
5. Infectious Diseases Clinic, Department of Biomedical Sciences and Public Health, Polytechnic University of Marche Medical School, Ancona, Italy
6. Clinical Microbiology and Virology Unit, Careggi University Hospital, Florence, Italy