Actually, it depends on where you live. I have more trouble with pneumonia in the fall than in the spring. My area has very wide fluctuations in temperature this time of year rather than in the spring. It is nothing for it to be 60 during the day and fall to 32 in the night.Pneumonia is mostly an early spring disease. It won't hurt to vaccinate them though...If you an get the vaccine. It's been in shortage lately.