The chairman of the congressional committee investigating the January 6, 2021, attack on the US Capitol by extremist Trump supporters has contracted Covid – but Thursday’s primetime hearing will proceed, according to a statement from the chairman, Mississippi congressman Bennie Thompson.

“While Chairman Thompson is disappointed with his Covid diagnosis, he has instructed the select committee to proceed with Thursday evening’s hearing. Committee members and staff wish the chairman a speedy recovery,” committee spokesperson Tim Mulvey said.

Meanwhile, two former White House aides are expected to testify at the hearing as the panel examines what then president Donald Trump was doing as his supporters stormed the US Capitol, according to a person familiar with the plans.

Matthew Pottinger, former deputy national security adviser, and Sarah Matthews, a former press aide, are expected to testify, according to the person, who was not authorized to publicly to discuss the matter and requested anonymity.

Pottinger and Matthews resigned immediately after the January 6 insurrection, which interrupted the congressional certification of Joe Biden’s victory over Trump in the election.

Lawmakers on the nine-member panel have said the hearing will offer the most compelling evidence yet of Trump’s “dereliction of duty” that day, with witnesses detailing his failure to stem the angry mob.

“We have filled in the blanks,” Illinois Republican congressman Adam Kinzinger said on Sunday. “This is going to open people’s eyes in a big way.”

He added: “The president didn’t do very much but gleefully watch television during this timeframe.”

A spokesperson for the committee declined to comment on the specific witnesses. CNN was the first to report the story.

Thursday’s hearing will be the first in the primetime slot since the 9 June debut, which was viewed by an estimated 20 million people.

Although questions remain about what exactly the former president was doing and saying as the mob descended on the Capitol, the House committee has been laying out a case that the attack was premeditated and was instigated by Trump.

Trump and his allies have insisted that the riot was spontaneous, and they did not know it was going to happen.

Along with Thursday’s hearing, the House committee told the Secret Service it has until today to turn over deleted texts sent the day before and the day of the insurrection.

The existence of deleted text messages may be central as the panel looks into how the Secret Service handled Trump and then vice-president Mike Pence as the breach unfolded.

Meanwhile, Trump’s former top strategist Steve Bannon is back in federal court on Tuesday for the second day of his trial. Bannon faces charges of criminal contempt of Congress after he failed to comply with a subpoena from the House committee.