Table 1. Vaccine effectiveness against hospitalisation due to COVID-19 in 65–79 and ≥ 80-year-olds, in overlapping 8-week-wide observation intervals, based on pooled estimates from Denmark, Navarre (Spain), Portugal and Norway, 1 October 2021–28 March 2022^a .

Age in years	Observation period	VE of complete primary vaccinationa		VE of complete primary vaccination  + first boostera
		Events/person-monthsb	VE (95% CI)	Events/person-monthsc	VE (95% CI)
65–79	1 Oct–25 Nov 2021	769/5,430,697	86.8% (84.5–88.8)	48/132,388	85.0% (78.6–89.5)
	1 Nov–26 Dec 2021	1,141/3,627,044	85.4% (78.8–89.9)	169/1,199,370	95.4% (92.9–97.0)
	1 Dec 2021–25 Jan 2022	766/1,261,165	77.8% (64.2–86.3)	597/3,623,380	95.3% (93.8–96.5)
	1 Jan–25 Feb 2022	515/386,221	55.3% (19.7–75.1)	1,429/4,981,833	91.4% (86.0–94.7)
	1 Feb 1–28 Mar 2022	334/261,264	44.3% (15.7–63.1)	1,972/4,783,200	87.6% (78.8–92.8)
≥ 80	1 Oct–25 Nov 2021	652/1,561,711	66.9% (60.1–72.6)	38/308,135	95.6% (88.0–98.4)
	1 Nov–26 Dec 2021	751/716,577	60.3% (49.7–68.7)	181/1,124,695	95.2% (90.6–97.5)
	1 Dec 2021–25 Jan 2022	620/262,138	52.4% (26.5–69.1)	884/1,752,544	93.3% (88.9–95.9)
	1 Jan–25 Feb 2022	544/148,922	46.2% (33.4–56.6)	1,938/1,901,312	87.8% (84.4–90.4)
	1 Feb–28 Mar 2022	399/117,721	38.8% (24.3–50.4)	2,493/1,819,768	82.0% (78.6–84.9)

CI: confidence interval; COVID-19: coronavirus disease; VE: vaccine effectiveness.

^a The values of VE were obtained by pooling VE estimates from Denmark, Portugal, Navarre (Spain) and Norway using random-effects meta-analysis. The supplementary material includes supporting numbers for the VE calculations (Supplement S2. Events and person-months), as well as the sample size per period and site (Supplement S3. Detailed site estimates).

^b The events per person-months presented in the column concern people who had primary vaccination status.

^c The events per person-months presented in the column concern people who, following complete primary vaccination, had also received the first booster and acquired booster vaccination status.