Table 6. Contrast pairwise comparison of mean anti-S-RBD IgG antibody titers (provided in S2 Table) of genders of study participants (males vs. females) by age within each sampling period.

Age group (years)	First period	Second period
21–30	0.91	0.021
31–40	0.15	NA*
41–50	0.45	0.56
51–60	0.012	0.12
61–72	0.25	0.20

Probabilities by t-tests and bootstrapping are provided, with significant associations shown in bold.

*NA, Not Applicable, due to the limited sample size of the 31–40 age group category in the second period.