January 23. Our tests were negative, but during the flight we both became unusually tired and slept almost continuously. In the evening, back in New York, I had a fever. Harmless fever, barely over a hundred. I shivered and tossed and turned all night, and J had to talk me into taking a Tylenol. I woke up a few hours later completely drenched in cold sweat and otherwise felt okay. Immune system at work.

I wonder if the immune system is some kind of Turing machine that, if only sufficiently programmed, can fend off any possible threat. Any being based on the same signature of life as ourselves. Or, conversely, is it possible, or has it ever happened, for an entire species to be wiped out by a pathogen?

We have tested again, continue to be negative. The fever comes in waves. Waves without particularly high amplitude, but miserable.