On a personal note, I hope Sir and the others are not affected badly by this and make a full recovery. I would surmise that because part of the leadership behaviour we expect to see involves being seen it would put him in a higher risk profile than many others, especially as a large proportion of the armed forces have been in the frontline of the Covid19 response. You can't really run the armed forces just using zoom or MS Teams.
On a professional note, it would be interesting to hear what levels of C19 infection have been in the Armed Forces and how it has been managed, especially given that many aspects of Armed Forces life would appear to carry a high risk of C19 infection such as shared messing facilities, dining, shared accommodation etc.
I've been heavily involved in the management of C19 in my civvy employment (3000+ employees- the majority working in public facing roles or cannot work at home, multiple sites across 5 counties including London) and so far we've sadly lost one employee (although many others have lost relatives) and the worst absence rate was 9% one week last winter. Aside from a few clusters at some sites ( predominately caused by car sharing) we've so managed it fairly,well although I dread to think how much it has cost.