Not sure what the nature or potential effect of the auto-immune disorder is, but I would consider blood counts in any attempt to try to balance risk. Has the 5-FU suppressed immune function so far? If I recall right, it is generally regarded as significantly less immunosuppressive than FOLFOX. But also consider that there can be suppression for a while after chemo is discontinued (when the virus may be more widespread). Also, things like where you live may be relevant — in the US the rate of infection is much higher in some areas than others, though the data is admittedly still very spotty. It’s a tough call, I wish you the best.
7/19: Rectal cancer: Initially staged as IIIA, T2N1M0
Initially approx 4.25 cm, low/mid rectum, mod. well diff. adenocarcinoma
8/22 -10/14 4 rounds FOLFOX neoadjuvant, 3 w/Oxiplatin (lots of side effects/reduced size est. 70-75%)
Switched to neoadjuvant chemorad in 11/19 (Xeloda and approx. IMRT, 60 Gy, 33 fractions)
Trying to achieve cCR.