https://en.wikipedia.org/wiki/List_of_largest_funerals says that the number of attendees for Churchill was "(6,000 at funeral service) 500,000", while the number for Elizabeth II was "(2,000 at funeral service) at least 1,000,000".
Agree "glandular fever" should probably be accepted. But certainly "infectious mononucleosis" should be accepted as that is the full name (in fact, that should be the official answer to the question, with "mononucleosis" accepted as a type-in).
https://en.wikipedia.org/wiki/Death_and_state_funeral_of_Winston_Churchill
Doing some research, it appears to be out of date. I updated the clue.