There may be some drawbacks to a promising vaccine by Pfizer

Clinical trials show the experimental vaccine could be more than 90 per cent effective in preventing infection

But Dr Jonathan Stoye, from the Francis Crick Institute in the UK, notes some issues.

Firstly, the vaccine requires two injections three to four weeks apart for full effectiveness -- and needs to be stored at minus 80 degrees.

He says that will severely complicate administering the vaccine to a lot of people -- particularly in warm countries.