The timeline below shows the total monthly seconds of airtime in which the title "Dr." appeared somewhere in the onscreen text of the ABC, CBS and NBC evening news broadcasts July 2010 through present. For most of the past decade, "doctors" (both medical and otherwise) have been interviewed onscreen for around 100-200 seconds each month. As the pandemic raged, it wasn't until March 2020 that the networks pivoted to bringing on large numbers of medical guests to discuss the pandemic, peaking in May and June. Since June of last year, NBC has kept the same amount of airtime devoted to doctor interviews month after month, while both ABC and CBS have sharply decreased their medical interviews.
Zooming to just the January 2020 to present period, the timeline below shows how ABC was the first to really ramp up its use of medical doctor guests, peaking in mid-April, while CBS peaked in late March and pivoted away much faster. In contrast, NBC doesn't peak until July and has been far more consistent in its use of doctors as interviewees over time.