Nor do I. I hoped that someone would find out about actual engineering changes made to the ship during an "Ask the Captain" session.
Holland America said, "Where feasible, we utilize enhanced filters and other technologies to mitigate risk." My assumption is that they find changes to be infeasible more often than not. Perhaps they have made no changes at all to a number of their ships.
I hesitated to book our August Zaandam cruise out of concern for covid, continued to wear a mask as I had been doing around town, was uncomfortable around crowds of unmasked people in planes, airports, tenders, and queues and I stayed out of elevators and theaters. I am now hesitate to book a January cruise because of covid, RSV and flu. Hospitals are filling up. A local parochial school reported 92 out of 300 students absent. I do not want to spend my cruise isolated in a cabin and I do not want to infect others.