OTOH a birthday party is unlikely to increase the risk much compared to work/school. In a few months that calculation might look very different though, e.g. Japan closed all its schools. But the US is more spread out so a lot of regions will be protected by their isolation.
This is the first one I've seen cancel that far out. (Well, I know another but I think there were other factors at play there as well.)
If turning 5, I'd probably keep it. On the other hand, you can scale back how you do it. The kid won't really know the difference. Besides, at that age, bigger isn't better. More friends is just overwhelming.
I've never met a 4 year old who wouldn't know what a birthday is.
Our daughters’ birthdays are coming up as well, and for now I’m keeping the plans, but am at least preparing in case schools cancel, etc.
FWIW, in response to the other reply, as a parent of 3 children under 6, I can say with recent experience that a birthday can be very important to a three year old (depending on the kid obviously).
Local birthday parties in cities without community spread are fine.
Once there is community spread if you city, then work from home, no birthday parties, maybe no school, etc.