There are several reasons why our upper respiratory tract is a hard area to target a vaccine.
"It's a separate immune system, if you like, which isn't easily accessible by vaccine technology," Professor Frazer told the Health Report.
Despite your upper respiratory tract feeling very much like it's inside your body, it's effectively considered an external surface for the purposes of immunisation.
"It's a bit like trying to get a vaccine to kill a virus on the surface of your skin."
Your skin, and the outer layer of cells in your upper respiratory tract act as a barrier to viruses, stopping them getting into the body.
And finding a way to neutralise the virus "outside" of the body is very difficult.
This is partly because only the outer layer of cells (the epthelial cells) get infected, which, compared to a severe infection of internal organs doesn't produce the same immune response, so is harder to target.
It's hard to produce a successful vaccine if the virus isn't activating a strong immune response.
And if a vaccine elicits an immune response that misses the target cells, the result could potentially be worse than if no vaccine was given.
"One of the problems with corona vaccines in the past has been that when the immune response does cross over to where the virus-infected cells are it actually increases the pathology rather than reducing it," Professor Frazer said.
"So that immunisation with SARS corona vaccine caused, in animals, inflammation in the lungs which wouldn't otherwise have been there if the vaccine hadn't been given."
