You are probably more likely to need travel insurance to Northern Ireland for reasons other than the coronavirus. What if a family member gets ill, or you yourself get ill, for any type of illness? Up to what point will the tour arranger allow you to drop the trip without penalty? The airline-purchased coverage would cover only the airline ticket, so if you are post-penalty date, you have to insure for the tour/retreat cost as well. "Regular" travel insurance protects against these situations, and also if you fall sick overseas.
If the coronavirus situation were dire enough that flights to northern Ireland were canceled, you would probably be reimbursed. If the retreat were canceled, likewise. But remember, the airline is responsible only for delivering you from airport to airport.
But, say, the virus is pretty widespread, but NOT serious in northern Ireland, so that everything is still on schedule, but YOU are nervous about flying in the confined space of the aircraft. The only travel insurance that would work in that situation is "cancel for any reason" travel insurance, which is the most expensive kind.
Yes, your credit card (if a high-cost one) MAY provide "regular" travel insurance, but I'd check it pretty carefully for evacuation costs, deductibles, etc. It almost certainly will not provide "cancel for any reason" travel insurance.
There are many companies offering travel insurance that will offer you a quote right on their website without registration - you just provide your state and age, so it's easy to check.