Table 4.

Antibody responses pre- and post-vaccination with quadrivalent recombinant protein influenza vaccine (RIV4) and quadrivalent inactivated egg-based influenza vaccine (IIV4) against influenza vaccine reference viruses^a according to influenza vaccine receipt during the previous season.

Prior influenza season (2018-2019) vaccination statusb	IIV4		RIV4		Post-vaccination GMT RIV4 vs IIV4 (95% CI)	P-value
	N	Post-vaccination GMT (95% CI)	N	Post-vaccination GMT (95% CI)
Influenza A(H1N1)pdm09
Prior season	166	80.2 (68-95)	163	165 (140-196)	2.1 (1.6 - 2.6)	<0.001
Not in prior season	46	93.9 (68-129)	40	243 (174-341)	2.6 (1.6 - 4.1)	<0.001
Influenza A(H3N2), Egg-based
Prior season	166	152 (131-176)	163	228 (196-264)	1.5 (1.2 - 1.8)	<0.001
Not in prior season	46	156 (118-207)	40	344 (254-465)	2.2 (1.5 - 3.3)	<0.001
Influenza A(H3N2), Cell-based
Prior season	166	81.6 (71-93)	163	181 (158-208)	2.2 (1.8 - 2.7)	<0.001
Not in prior season	46	78.0 (60-101)	40	227 (172-299)	2.9 (2.0 - 4.3)	<0.001
Influenza B (Victoria)
Prior season	166	73.3 (62-86)	163	81.1 (69-95)	1.1 (0.9 - 1.4)	0.391
Not in prior season	46	99.8 (73-136)	40	139 (100-194)	1.4 (0.9 - 2.2)	0.145
Influenza B (Yamagata)
Prior season	166	101 (86-118)	163	172 (147-202)	1.7 (1.4 - 2.1)	<0.001
Not in prior season	46	126 (94-171)	40	332 (241-458)	2.6 (1.7 - 4.1)	<0.001

Abbreviations: IIV4, Quadrivalent inactivated influenza vaccine; RIV4, Quadrivalent recombinant influenza vaccine; GMT, Geometric mean titre.

^aInfluenza vaccine reference viruses: A/Brisbane/02/2018 (H1N1)pdm09, A/Kansas/14/2017 (H3N2), B/Colorado/06/2017 (Victoria lineage), and B/Phuket/3073/2013 (Yamagata lineage) vaccine antigens.

^bGMT and GMT ratios were calculated using linear mixed models adjusting for age, hospital, and immunocompromised status. Statistically significant findings are shown in bold.