A phase III, open label, multicenter study of GSK Biological herpes zoster HZ/su candidate vaccine (GSK1437173A) administered intramuscularly on a 0 and 2 month schedule evaluating the immunogenicity, safety and reactogenicity in adults 65 years of age with a previous Zostavax vaccination 5 years earlier, compared to group-matched adults not previously vaccinated with Zostavax.