(New Zealand) I was recently part of a medical trial relating to getting a covid vaccine at the same time as, or 6 weeks after a flu jab. Pfizer funded, double blind, decent sized pool, one of many countries participating, tra la. Results aren’t available publicly yet, but work is being done on the viability of piggybacking them, at the very least.

Anecdotally, I had covid and flu jabs at the same time (soreness at the site etc (and later confirmed when unblinded) and placebo at 6 weeks, no reaction more than swelling at the injection site. Chatting with others in the waiting room, sounded like it was similar in our cohort, at least.