Japan is now reporting that a female tour-bus guide has been diagnosed with COVID-19. Normally, individual infections aren’t news at this stage of the virus’s spread. Except that this patient was already being counted in the “recovered” population. She had contracted the disease initially in January, received treatment, and was declared recovered and released on February 1. Now, a little over three weeks later, she’s a patient again. 

What does this mean? Well, it’s too soon to tell for certain, but there are a few possibilities, in roughly increasing order of concern:

  • This might be a one-off event, perhaps due to idiosyncrasies of the patient’s immune system. Even with diseases that typically confer lasting immunity, that doesn’t quite work right for a small fraction of people.
  • The determination that she was actually recovered might have been wrong. She was sick, she got treatment, she seemed better and was released, but she wasn’t actually ”recovered” in the first place. In the best case, this would also represent a one-off event; a more serious problem would be the next option…
  • The determination that she was actually recovered might have been wrong, because this disease is capable of a latent period or biphasic infection. Some diseases do this on a regular basis, with a sham recovery followed by secondary disease. The mechanics differ from pathogen to pathogen. Some (like anthrax) are just naturally capable of producing two rounds of illness. Others have the capacity to go dormant while remaining in a hidden reservoir, re-emerging later to cause a renewed illness; in some cases, this makes infection effectively permanent (such as herpes zoster or HPV). Regardless of the mechanics, if this virus does experience viral latency or biphasic disease, control is effectively impossible because “recovered” cases might still be (or become) infectious.
  • Or, as a last case, it’s possible that this virus does not confer significant immunity to subsequent exposure. If that’s the case, not only will we start seeing a lot more re-infections, but the likelihood of an effective, quickly-developed vaccine takes a huge hit.

The bulk of the patient history for COVID-19 is still based in China. We don’t have large numbers of recovered patients elsewhere, especially recovered patients with likely pathways for re-exposure. But we’ll start seeing the potential for that in Italy, Japan, and South Korea in the coming weeks. And that may tell us a lot about the direction this outbreak will take.

Regardless, this still is not time to panic. It’s never time to panic. But it is time to start considering how to respond to large-scale disruption, like the closing of schools or businesses for extended periods of time (for example, Japan is considering closing all schools for the entire month of March).

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