** Sero- konvertering = negativ prævaccination HI- titer og postvaccination 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.