Table 7. Correlation between RFFIT and ELISA assay results in the non-boosted study population.

	Two years after vaccination (2007)	Three years after vaccination (2008)	Four years after vaccination (2009)
Non-boosted population (n)	489	402	365
GMT
RFFIT	1.10	1.11	1.00
ELISA	1.01	1.31	1.39
Person’s r coefficient (95%CI)	0.82 (0.79–0.85)	0.71 (0.66–0.76)	0.62 (0.55–0.68)
Participants with titers >0.5 IU/mL [n (%)]
RFFIT	413 (84.6)	351 (88.0)	312 (85.7)
ELISA	387 (79.3%)	347 (87.0%)	333 (91.5%)
Kappa coefficient	0.61	0.54	0.42