Can people who recover from a bout with coronavirus become infected again - and again?

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https://www.nytimes.com/2020/02/29/health/coronavirus-reinfection.html

They Recovered From the Coronavirus. Were They Infected Again?
In a few cases, patients again tested positive for the virus after they were no longer ill. But little is known about the virus, and it’s possible that testing flaws may be to blame.
By Apoorva Mandavilli
Feb. 29, 2020, 5:00 a.m. ET

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“I’m not saying that reinfection can’t occur, will never occur, but in that short time it’s unlikely,” said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York.

Even the mildest of infections should leave at least short-term immunity against the virus in the recovering patient, he said.

More likely, the “reinfected” patients still harbored low levels of the virus when they were discharged from the hospital, and testing failed to pick it up.

In four medical professionals exposed to the virus in Wuhan, China, the epicenter of the epidemic, a test that detects the viral genetic material remained positive five to 13 days after they were asymptomatic.

This does not necessarily mean that they were still able to infect others, however.

The PCR diagnostic test is highly sensitive and can amplify genetic material from even a single viral molecule. As such, the test could merely be picking up fragments of the virus.

PCR tests may detect remnants of the measles virus months after people who had the disease stop shedding infectious virus, Dr. Krammer said.

The other possibility is that the negative test was done poorly, or the samples were stored at a temperature at which the virus deteriorates. The throat swab may also simply miss the virus that is hiding elsewhere in the body.

“A virus test is positive if the virus was there on the swab in sufficient quantities at the time you swabbed the person,” said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health.

Dr. Lipsitch offered an analogy: a jam jar with mold on top. Scraping off the surface might give the impression that the jam is now mold-free, but in fact the jar may still contain mold that continues to grow.