TABLE 3.

Interval categorization into “level” of anti-SpikeS1-IgG and anti-RBD ranges of all participants.

Level	Interval [unit]	Participants at T2	Participants at T3
IgG level	Interval [BAU/ml]	N	N
–1	IgG < 25.6	154	98
0	25.6 ≤ IgG < 35.2	4	6
1	35.2 ≤ IgG < 100	0	15
2	100 ≤ IgG < 200	0	9
3	200 ≤ IgG < 300	0	10
4	IgG ≥ 300	0	20
RBD level	Interval [% inhibition]	N	N
–1	RBD < 20	93	65
0	20 ≤ RBD < 35	0	5
1	35 ≤ RBD < 50	0	2
2	50 ≤ RBD < 65	0	2
3	65 ≤ RBD < 80	0	3
4	RBD ≥ 80	0	16

The detectable ranges of anti-SpikeS1 and –RBD IgG antibody values are categorized into six intervals, labeled from –1 to 4 (referred to as “levels” in the data analysis). The limit of the “–1” level is defined by the manufacturer’s test limit on negativity. The limit of the next higher level “0” follows directly upwards and includes the gray area of the corresponding test (below the positivity threshold). The limits of the other levels are chosen arbitrarily (“1,” “2,” “3,” and “4”) and represent the remaining linear test range in approximately equal intervals.