"Alright, I've done the numbers, China has 1.4 billion people and they've had just over 3,000 deaths from the coronavirus and he's telling us we're going to get 96,000 deaths out of 25 million people?"
When Sam said she "didn't believe the numbers coming out of China", Kochie gave her an eye roll.
"That is such a lame argument to back up a personal opinion," he said.
Nat Barr pointed out that Sam believing the death toll in China was higher than reported was similar to Koch slamming the economist's predictions.
"But he's predicting those, they're not facts." Koch said.
While Kochie claimed the predictions were "irresponsible", Mr McKibbin told 7NEWS the study discusses multiple scenarios.
"They are the assumptions of different combinations of infection rates and mortality rate from historical pandemics," he said.
The economist referred to the “regular flu” which killed 5,000 people in Australia in 2019.
"I guess David Koch didn't read the paper."
The on-air slanging match comes after Sam shared a sweet letter from a viewer on Tuesday after she returned to work on Sunrise on after taking some time off sick.
The popular TV presenter, 43, sharing a photograph of the letter from a young admirer to her Instagram stories.
"Because there's so much awful stuff on social media, here's something lovely," she wrote over a pic of the handwritten note.
"Every Monday-Friday I wake up at 5.30am and tune in to Sunrise," Samantha's admirer, a 12-year-old boy named Joseph had written in his thoughtful letter.
"I've been watching it now for 2 years and everyday she looks so pretty and that's why I admire her. That's pretty much all I have to say," he finished.
Clearly moved, Sam responded to the letter by writing: "This is all you needed to say... thank you Joseph xx"