Serious. Might be too late. Hopefully they are going to disinfect the place before resuming the classified work.
The article says people have to be escorted in and out of the place. Does sound serious.
When you get a classified "briefing", the "caveats" spell out punishments and penalties. They seek to impress upon you the grave consequences that could occur if security was breached. Having worked in classified spaces, I have a very strong agreement with the potential calamity that could occur with a breach. Los Alamos has been terribly sloppy over the last 10 years. I wouldn't be surprised if the consequences of that sloppiness cause the kinds of horrific damage to the United States that is implied in the caveats.