Why no mention of the 1918 influenza pandemic?

With all the recent information about the 1918 flu pandemic (because of a potential bird flu pandemic), I wonder why Walter never mentioned it in his letters.

He was in England from May 1915 (foot injury at 2nd Ypres) until September 1919 when the Machine Gun Corps left for India, so he was in the thick of the flu crisis. How were his and May's families affected?

I'm surprised Walter didn't catch it, since he seemed prone to every other thing flying through the air during his lifetime (diphtheria, typhoid fever, various war injuries). Perhaps no one close to him was affected, so it didn't warrant a mention. Still, I wonder.