J & J and Astra Zeneca are the ones that will be most vulnerable to mutations, and the most sluggish to respond to necessary changes. The single shot regimen has it's advantages, but as a consumer, I am happy that I got the Moderna (wife received Pfizer). I almost wish they would designate JJ for the younger crowd (u40) who are naturally less likely to have severe COVID, but we haven't reached that point in the priority list.