When Omicron burst onto the scene late last year, scientists were shocked at how many mutations it had compared to previous variants.

We now know that it's way more transmissible than previous variants and less nasty than Delta, although that hasn't stopped it from causing a lot of severe disease and death.

But biology isn't static and Omicron has continued to evolve. First came BA1, then came a new wave of BA2 and now we're starting to see another new subvariant: BA4.

So on today's Coronacast, what is BA4, where did it come from and how much of a worry is it?

Also on today's show:

* What's going on with the hepatitis condition in kids? Is it being caused by COVID-19?