** Sero- konvertering = negativ præ- vaccinations HI- titer og post- vaccinations HI- titer ≥ 40; signifikant stigning = positiv præ- vaccinations- HI- titer og mindst en 4 gange stigning i post - vaccinations- HI- titer.
** Seroconversion = negative pre-vaccination HI titer and post-vaccination HI titer ≥ 40; Significant increase = positive pre-vaccination HI titer and at least a 4-fold increase in post-vaccination HI titer