I'm inclined to believe they're sweeping for a rogue nuke, dirty bomb or radiological outbreaks because they're being seen over critical infrastructure, military installations, Trump's properties, and the Capitol building in Washington DC.
It would explain a lot and if you watch the livestreams of the House Hearings it is clear they cannot tell the local elected officials everything. However, I would not put it past the government to pull a stunt like this to cry about budget deficits on handling drones.
I remember seeing videos on Twitter back in November of 2019 of people falling down ill in China and some grumblings about a virus and then Covid happened. The timing and media reporting is similar in that there's reports of an unknown threat. An invisible enemy that's unprecedented, nothing like it. Hoping this doesn't get out of control and lead to another advancement of police state tactics and exercises on the public like Covid was.
There were exercises similar to this in virus outbreaks just before Covid:
https://www.energy.gov/nnsa/articles/nnsa-working-federal-state-and-local-partners-hold-major-radiological-incident