ah ok i mistunderstood what the group head is. if they are both permanently in contact with the water in the boiler then it would depend a lot on the water quality. Water with only a little conductivity (<100µS/cm) would not be a problem for pure aluminium or most alloys, since the aluminium would passivate much quicker than the corrosion could dig into it.
i would assume that a vessel made for boiling water is made of a highly corrosion resistant alloy but i can not know for sure.
If you mean an Immune escape that is not a real problem for rabies because that virus has a slow evolution as you can tell from the fact that the same vaccines that were used in the 80s are still used today. Compare that for example to flu or Covid-19 vaccines where even two year old vaccine types are considered outdated and not used anymore.