Thread by @DrMattMcCarthy

UPDATE: Coronavirus has mutated into a new variant, B.1.1.7, that has the world's attention because it may be more contagious.
Some thoughts on where this came from and how it impacts patient care: 1/

The novel #coronavirus typically acquires a mutation every few weeks. The new variant is interesting because it seemingly developed a bunch mutations all at once: 17 mutations in viral proteins, including 8 changes in spike protein, the target for all of our vaccines. 2/

Why would a flurry of mutations suddenly emerge? The focus now is less on unique properties of #coronavirus and more on unique human hosts: patients with impaired immune systems who are chronically infected and unable to clear the virus. 3/
sciencemag.org/news/2020/12/u…

This is a big group. It includes patients with cancer receiving chemo, those rheumatologic disease, and many others. These people can remain persistently infected with #coronavirus for months & can serve as an incubator that accelerates viral evolution: 4/
nejm.org/doi/full/10.10…

Here's what happens: Rather than moving along after 10 days or so, coronavirus remains active inside a subset of patients with weakened immune systems, testing and teasing human antibodies and T cells, figuring out how to change shape to evade capture. The immune system fails. 5/

Failure takes time; the battle allows the virus to mutate again & again within a single patient, before spreading on to others. Thankfully, B.1.1.7 is back to mutating at a slower pace. That could change, however, if it infects another patient with profound immune impairment. 6/

None of this is a surprise. Since the spring, we have known #coronavirus behaves differently in patients with immune impairment. These people can remain infectious for twice as long (20 days) as symptomatic patients without immune impairment (10 days). 7/
cdc.gov/coronavirus/20….

This variant hasn't been found in the U.S., but it is almost certainly here. The CDC just noted that viruses have been sequenced from only 51,000 of 17 million US cases. Now that we're looking, we'll soon find it. Don't stress. We'll track the changes. 8/
cdc.gov/coronavirus/20…

Key point: Doctors should take note when treating a #COVID patient who has severe immune impairment; the virus may be difficult to eradicate. The longer it lingers, the more opportunity it has to mutate. These patients may require unique precautions and expert consultation. 9/

Takeaway: There are many unknowns with this variant, but we know what to look for. I'm optimistic that vaccines will remain effective because they induce so many different & powerful immune responses. The new viral variant may evade antibodies, but it will hard to outrun T cells.