A few more anecdotes from my experience with the Super Cooties...
More than a year after catching the bug in October 2021, I finally feel like I'm back to the level of fitness I was before getting sick. Took about a year.
However I need more time to recover. I used to be able to ride or run almost every day. Now I usually need a full recovery day after any bike ride or run longer than an hour. Friday I did a 20 minute easy warmup on the indoor trainer, a 5.5 mile run at moderate pace, another hour on the indoor trainer at easy effort to cool down and loosen up some tight hip and quad muscles. Felt great before bedtime. But Saturday I was wiped out and could hardly get out of bed. That's been typical for the past year since recovering from COVID.
I haven't been able to handle long rides, including group rides, since earlier in 2021. If I join friends for a casual ride, between the commute to and from the meetup, the ride itself, and maybe socializing during and after, that's often a commitment of 4-6 hours or longer. I just don't have the energy for that anymore. But another factor is chronic neck pain from cervical spine stenosis, which limits my rides to 60-90 minutes.
But age is probably another factor. I'm 65 now and significant gains in fitness are almost impossible. I'm mostly treading water and trying to minimize the loss of fitness. Very different experience compared with 2015 when I resumed cycling at age 57 after a 30+ year hiatus from riding and running. From 2015-2020, I experienced steady, and sometimes dramatic, improvements in fitness. But nobody beats aging, we can only delay the inevitable with a bit of luck, good genetics, diet, exercise and rest.