Commutability between ELISA IgG endpoint titres and EU
REGRESSION
The orthogonal linear regression analysis and fitted equation used for conversion indicated that the value of 1:1600 endpoint titre measured 17 days post-vaccination (exp of ln 7.38), the threshold associated with 74% protection in young adults, corresponded to the value of 6.6 EU (95% CI, 5.7–7.4) [exponent (exp) of ln 1.89 (95% CI, 1.74–2.01)] (The 4.5 EU (exp of ln 1.5) measured ≥2 weeks post-vaccination, at a median time of 18.5 weeks after vaccination, and associated with 52% protection in children aged 2–4 years corresponded to 1:1072 titre (95% CI, 1:937 to 1:1226).