NSW Health authorities are dealing with a new COVID-19 outbreak that appears to have slipped through our borders via a driver who transports international flight crew.

And late on Tuesday, NSW Health said two people staying in a quarantine hotel may have been infected from people staying in a room next door.

Further south in Melbourne, contact tracers are also trying to work out how many people in a Southbank apartment are infected.

So on today's Coronacast, how might this sneaky leaky virus be circulating?

Also on today's show:

* What we know about myocarditis and mRNA vaccines in young people

* I'm under 50 and had AstraZenca as my first shot. If I get the chance of a Pfizer shot before my 2nd, should I take it or get my 2nd AstraZenca?