By Clare Wilson.
The omicron variant may be less likely to be detected by thelateral flow tests.
The George Clerk is pictured.
Is it possible to test positive without being infectious?
If you have had three doses of vaccine, a positive LFT result means you are infectious to other people because of the large quantities of virus in your nose or throat. The virus must be growing inside your cells.
For days to weeks after an infectious disease, the results of the tests are positive because they can detect tiny quantities of the virus's genetic material.
How have testing rules changed?
The surge caused by the omicron variant has led many countries to ease their restrictions on people with covid-19. If you get a negative result on two LFTs, the period of isolation for you in the UK has been cut from 10 days to seven. The work must be done on days six and seven.