American health regulators have paused the use of the Johnson & Johnson coronavirus vaccine, following reports of rare blood clotting in six recipients.

Like the AstraZeneca vaccine, Johnson & Johnson is what's known as a viral vector vaccine - where another virus is used like a taxi to deliver a bit of coronavirus to help teach the immune system.

So on today's Coronacast, what are viral vector vaccines and could the rare blood-clots be a problem with them more broadly?

Also on today's show:

* What do the data show regarding the risks of clotting for people over the age of 50?

* What can we learn from the US vaccine rollout? (We hear from special guest Anthony Fauci, who Tegan interviewed as part of an event presented by UNSW)