The Centre said lateral flow tests, which includes rapid-antigen and home-antigen tests, can detect Covid from the third day after exposure to the virus to day eight while the RT-PCR test can diagnose the infection for up to 20 days.

At a press conference, the Indian Council of Medical Research (ICMR) Director-General Dr Balram Bhargava said on the first day one will test negative whatever tests they undertake. "It takes time for the virus to grow in your system and that is known as the latent period. From day three it will be detectable in the Lateral Flow Tests and up to day eight which is the infectious period.