Board Thread:Questions and Answers/@comment-104.33.82.219-20171004222613/@comment-1738746-20171005092013

That's actually a really good question that I'm not sure of the answer to. Best place to ask would be on the forum itself, though I will also investigate this to see how it works! Until then, you could try but it's best to Hide your egg until it loses the sickness.

Edit: From the forum, Ward can be used on sick eggs, and it doesn't prevent sickness but rather prevents dying from it.