Interseason waning of vaccine-induced hemagglutination inhibition antibody titers and contributing factors to pre-existing humoral immunity against influenza in community-dwelling older adults 75 years and older

Table 5 Interseason antibody waning estimated using current season vaccine strain antigens^a

Vaccine strain	Consecutive two seasons	Unadjusted	Adjusted^b
IAV-H3N2	2014–2015 (n = 49)	0.27 (0.20–0.36) (p < .01)	0.25 (0.14–0.44) (p < .01)
IAV-H3N2	2015–2016 (n = 52)	0.25 (0.20–0.33) (p < .01)	0.21 (0.12–0.35) (p < .01)
IBV	2014–2015 (n = 49)	0.18 (0.15–0.22) (p < .01)	0.17 (0.12–0.24) (p < .01)
IBV	2015–2016 (n = 52)	0.96 (0.74–1.24) (p = .74)	0.67 (0.40–1.12) (p = .12)
IAV-H1N1	2016–2017 (n = 78)	0.58 (0.50–0.68) (p < .01)	0.59 (0.45–0.77) (p < .01)

^aRatios of pre-vaccination HAI antibody titers measured using current season vaccine strain antigens over prior season post-vaccination HAI titers measured using prior season vaccine strain antigens among participants who completed the study in the two consecutive study seasons
^bAdjusted for age at prior study season, sex, race, and education

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