This gets complicated, live virus and mRNA type vaccines that hijack a small number of your cells for a full immune system response aren't as far as I know normally used for people that age, see https://www.cdc.gov/vaccines/schedules/hcp/imz/adult.html and note "zoster live" has been removed from the US market.
On the other hand, they might just wring out the best response possible at a slightly greater risk. Here I'm assuming your parents shouldn't try a PRC vaccine, so it's virus vector Russian or mMRA Pfizer, both essentially accomplishing the same thing, both with high overall efficacy.
Or look at it this way: if they don't get a good result from either of these two vaccines, they're not likely to fair well from a real infection. Maybe. We really don't known why even at their age most people survive.
The other factor is how much you trust quality control. Pfizer > Russia >> PRC in my book, but I have absolutely no read on Russian quality. But also note Pfizer/BioNTech is useless if not properly handled to its strict temp and physical requirements.
On the other hand, they might just wring out the best response possible at a slightly greater risk. Here I'm assuming your parents shouldn't try a PRC vaccine, so it's virus vector Russian or mMRA Pfizer, both essentially accomplishing the same thing, both with high overall efficacy.
Or look at it this way: if they don't get a good result from either of these two vaccines, they're not likely to fair well from a real infection. Maybe. We really don't known why even at their age most people survive.
The other factor is how much you trust quality control. Pfizer > Russia >> PRC in my book, but I have absolutely no read on Russian quality. But also note Pfizer/BioNTech is useless if not properly handled to its strict temp and physical requirements.