[1] In OTL, Humphrey died of bladder cancer in 1978, but a tumor had been found on his bladder as early as 1967:
https://www.minnpost.com/politics-policy/2011/05/final-chapter-hubert-humphrey-returns-public-life/
[2] You may recall at the very beginning of the TL I mentioned that Humphrey was staying at a motel only a few miles from Fermi at the time of the accident. Maybe this is a little ASB, but it’s plausible that Humphrey’s visit could have led to an advancement of his cancer, which in OTL eventually killed him in 1978. Interestingly, there is evidence that the incidence of bladder cancer increased in Ukraine after Chernobyl:
https://www.ncbi.nlm.nih.gov/pubmed/15010889
[3] Humphrey really was sick with the flu in July in both OTL and ATL, but in September in ATL he was actually receiving radiation treatment during the three weeks he was “sick”. The public was kept unaware of this.
[4] In OTL, starting in 1972, Humphrey was treated with an anti-cancer drug, and in 1973 he had radiation treatment:
https://www.washingtonpost.com/archive/politics/1977/08/19/humphreys-cancer-is-inoperable