Here's yet another approach using the track matte key effect. You'll need three tracks. Track 1 is the background. Track 2 is the interview footage. Track 3 is the matte that will determine which portions of track 2 to keep.
For track 1, you can blur the interview footage as Sidd suggests. Or, you can save a frame from the video and edit it in Photoshop or other editor to create a uniform background that matches the color of your background. In my example, I used Photoshop's content aware fill to eliminate the person and followed that by the average blur effect to make a uniform matching background image.
Place the interview footage on both track 2 and track 3. On track 2, apply the Track Matte Key effect and set the matte property of that effect to "track 3".
On track 3, apply the sixteen point garbage matte effect. In the applied effects panel. click on the header for the garbage matte you just applied. The points should show up on in the monitor panel. adjust the points by dragging with the cursor to closely surround the subject. It should look something like this:
problem_masked.JPG
Because the subject will not be sitting perfectly still, the mask will need to be adjusted. Enable key frames for the garbage matte. Advance the video one frame at a time and adjust any of the garbage matte points that need it.
One final step. The small area around the subject that was not removed by the garbage mask will be visible and most likely stand out. You can improve the results by applying the Chroma Key effect to Track 2. Select the color for the effect from a typical value close to the head. Adjust the effect parameters to get the best key while keeping the subject intact. Expect that it won't be perfect. But, it may be reasonable. Here's the final result:
problem_final.JPG
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