Low % cv - NDV Elisa report

I would be grateful if somebody can interpret NDV Elisa report that show very low % CV - 0 up to 6 % - baseline data of that %CV 20-60 , where as the mean titer was normal being in line with the baseline data and was 10.000-20.000. -BB Flock - 26 week-old. - Vaccinated at 23 week - samples collected 3weeks post vaccination -.live vaccine -Ma5 and colone 30 -spray . Valid Elisa test . What is the reason that render %CV low .