Table 2. Distribution of baseline characteristics of the study cohort, i.e. people aged ≥ 65 years living in Finland during September 2022–August 2023 (n = 1,191,871).

Characteristic	Number	Proportion (%)
Age in years
65–79	886,240	74
80–110	305,631	26
Region of residence
Helsinki-Uusimaa	285,668	24
Åland	6,655	1
Northern and Eastern Finland	304,279	26
Southern Finland	281,241	24
Western Finland	314,028	26
Sex
Female	663,141	56
Male	528,730	44
Hospitalised between September 2020 to August 2022
No	923,953	78
Yes	267,918	22
Presence of severely immunocompromising conditions^a
No	1,090,769	92
Yes	101,102	8
Number of highly predisposing medical conditions^b
0	927,126	78
1	178,731	15
2–3	86,014	7
Number of moderately predisposing medical conditions^c
0	650,124	55
1	323,423	27
2	127,813	11
3–8	90,511	8
Long-term care
No	1,139,655	96
Yes	52,216	4
Number of monovalent COVID-19 vaccinations before the study
2	64,932	5
3	467,769	39
4–5	659,170	55
Last laboratory-confirmed SARS-CoV-2 infection before the study
No prior infection	1,110,107	93
Pre-Omicron infection	13,453	1
Omicron infection	68,311	6

SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.

^a Severely immunocompromising conditions are described in Supplementary Table S2.

^b Highly predisposing medical conditions are described in Supplementary Table S3.

^c Moderately predisposing medical conditions are described in Supplementary Table S4.