chazzledazzle,

I don't recall that report, but any who do not clear the virus (or any pathogen) remain reservoirs for continued mutation. If the patient immune response remains ineffective, the virus will persist and develop immunity to the administered Regeneron mAbs.

Quote:

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Furthermore, laboratory experiments have shown that some of those mutations help the virus bypass detection by antibodies.

"Toward the very end of his life, he was treated with monoclonal antibodies, from Regeneron," Li says. "And shortly thereafter, we saw evidence that suggested the virus was developing resistance or escaping from these antibodies as well."

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Mutations happen. Those mutations which allow the virus to evade host or externally administered antibodies will persist and become dominant, just as the researchers observed.