Simple linear regression models were used to analyze the effect of age on nAb titers separately for male and female HCWs before vaccination in H1N1 2017-18 season (A), 28 days post-vaccination H1N1 in the 2017-18 season (B), before vaccination in H1N1 2018-19 season (C), 28 days post-vaccination H1N1 in the 2018-19 season (D), before vaccination in H3N2 in the 2017-18 season (E), and 28 days post-vaccination H3N2 in the 2017-18 season (F) before vaccination in H3N2 in the 2018-19 season (G), and 28 days post-vaccination H3N2 in the 2018-19 season (H).