A lot of disease circulation happens at a global level, and it has a strong seasonality component.
Last winter, if you remember, even in the UK, many people were still being very careful. And in other places there still were restrictions and strong recommendations for masking, etc. There are still plenty of universities in North America that are requiring masking. Travel was still low for some time and that drives the movement of viruses too.
Spring is typically the normal downturn of viruses and the like, which was the reason many areas decided to begin removing restrictions at that point.
We are now moving into a more normal flu season. The last few years flu was down significantly, partly because of restrictions, but also pushed out to some extent by covid.
And then we are seeing a lot more things like RSV in children, and that is because there is a large group that has never been exposed normally, so they are all getting sick at once. Now the normal seasonal cycles are starting to reassert themselves too.
It would be interesting to know what is going on in places like China where they are still having significant restrictions.