1. Laboratory of Clinical Virology, School of Medicine, University of Crete, 71003 Heraklion, Greece
2. St. George's, University of London, London SW17 0RE, UK
3. Vienna Vaccine Safety Initiative, D‑10437 Berlin, Germany
4. First Department of Paediatrics, University of Athens School of Medicine, 11527 Athens, Greece
5. Department of Paediatric Radiology, ‘Mitera’ Children's Hospital, 15123 Athens, Greece
6. Paediatric Intensive Care Unit (PICU), ‘Aglaia Kyriakou’ Children's Hospital, 11527 Athens, Greece
7. Neonatal Department, ‘Alexandra’ Maternity Hospital, 15123 Athens, Greece
8. Paediatric Intensive Care Unit (PICU), ‘Penteli’ Children's Hospital, 15236 Penteli, Greece
9. 2nd Department of Internal Medicine, ‘St Panteleimon’ General Hospital of Nikaia, 18454 Piraeus, Greece
10. Department of Ophthalmology, Royal Cornwall Hospitals, Cornwall TR1 3LQ, UK
11. Department of Paediatrics, ‘Penteli’ Children's Hospital, 15236 Penteli, Greece