Jury members and others have been tested before the start of each day of the trial so far.
"I suppose it was predictable that in the course of this trial we were going to lose someone," said Justice Osborne.
He said bio-cleaning was carried out regularly, and the jury room would be given an extensive clean. Another courtroom would be made available for the jury to use.
Prasad, 39, denies murdering Fijian-born Faiz Ali in an alleged hammer attack on February 21, 2021. The defence said Prasad was not guilty of murder because he did not have murderous intent.
The Crown alleges Prasad broke into Ali's home and waited for him before attacking him with a hammer and a knife when he arrived. Ali received 38 wounds including blunt force injuries to the head which "caved in" his skull, the Crown said.
The Crown is calling evidence from 27 witnesses and may finish presenting its case on Thursday.
The first witness on Wednesday was a neighbour, Heena Mehra, who said she heard screaming, shouting and "noises consistent with a fight". She said: "I heard noises as though they are hitting each other."
Another neighbour of the Armagh St property, Rachel Haselden, told of seeing a man leave. He told her: "I won't harm you. That man was having an affair with my wife." She said he seemed rational, "but there was blood, and he was holding a weapon".
Barnaby Hawes and John Whitcombe appear for the Crown; James Rapley QC and Ben Walker appear for Prasad.
