Table 1. Number and proportion of observations with reactive antibody titre ≥40 by age groups in pre- and post-pandemic samples and difference in proportions between pre- and post-pandemic samples.

	Pre-pandemic		Post-pandemic		Difference
Age groups (years)	N/Total	% (95%CI)	N/Total	%, (95%CI)	%, (95%CI)
18–29	16/128	12.5 (7.3–19.5)	28/66	42.4 (30.3–55.2)	29.9 (16.7–43.2)
30–39	3/98	3.1 (0.6–8.7)	11/51	21.6 (11.3–35.3)	18.5 (6.7–30.3)
40–49	3/132	2.3 (0.5–6.5)	14/68	20.6 (11.7–32.1)	18.3 (8.4–28.3)
50–59	7/167	4.2 (1.7–8.4)	6/59	10.2 (3.8–20.8)	6.0 (−2.3–14.3)
60–69	7/199	3.5 (1.4–7.1)	2/48	4.2 (0.5–14.3)	0.6 (−5.6–6.9)
≥70	3/121	2.5 (0.5–7.1)	2/42	4.8 (0.6–16.2)	2.3 (−4.7–9.3)