Vaccine groups 18–55y: 2 x low dose (n = 50) 18–55y: 2 x std dose (n = 50) 56–69y: 1 x low dose (n = 30) 56–69y: 1 x std dose (n = 30) 56–69y: 2 x low dose (n = 30) 56–69y: 2 x std dose (n = 30) ≥70y: 1 x低剂量(n = 50)≥70Y:1 x std剂量(n = 50)≥70Y:2 x低剂量(n = 50)≥70Y:2 x std剂量(n = 50)