Depends how and where it is used. The USSR had IIRC the world's largest and most advanced program at the time, so due to MAD I doubt that Hitler would use it there, as the Germans were well aware of and scared of the Soviet program. The British would be the prime target in 1940-41, as they had limit means to retaliate at the time (weak BC and less developed BW program...Operation Vegetation wasn't viable until 1943-4 IIIRC) AND they could be isolated from the continent once the disease spread.
But then Hitler wanted accomodation with Britain, not all out war. If we wanted to wipe out the Brits, he could have done so with minimal risk of successful retaliation during the Blitz in 1940-41 with existing chemical weapon stocks (German mustard gas developments would have made London uninhabitable in 1940 if used); but again Hitler was driven by MAD, so refrained IOTL.
Also Germany specifically didn't have a Bio-weapons program IOTL because of Hitler's disgust with the idea, echoed by the Prussian generals, so it would take a mighty change for Germany to get in on bio-weapons; it only did so belated IOTL as a deterrent and was behind everyone else, even the US.
I do remember that Stalin had amassed quite a stockpile of chemical weapons, as did the US, following WWI. As far as whether or not the Reich wanted to wipe out the brits or not has been a topic of some debate over the years. Given Hitler's psychological profile, and his megalomania, only unconditional surrender would have been satisfactory.
In the beginning of the Reich, there was a ranking SS medical officer that had written a paper on the use of disease as a weapon. As I recall, he did use the mathematical models of the day to show its effect on England. I can't recall the name, Clauberg comes to mind , but I think he was mostly involved in sterilization and euthanasia.
The general disdain for CBW, and not just in Germany, kept much of it off the battlefield. But as Japan was using at least CW effectively in China and other parts of Asia, the allies maintained a stockpile, and as I recall conducted experiments in Australia and NZ on civilians. Germany and Italy failed to get onto the CBW bandwagon until late and only after sheer deperation set in.
Which brings about a more interesting question, at least in my mind. What would it have taken to change Hitler's mind and look towards Biological warfare?
Andrew