Thursday, December 24, 2020

Don't Panic About The New UK Coronavirus Strain

 As ever, I use the word "strain" in the title here with some hesitation, because it hasn't been shown (yet) conclusively to affect pathogenicity or transmissibility, but some very good stuff in yesterday's This Week In Virology Episode 697. This doesn't cover all of it, but it hits the big points I think people are most interested in:

  • Increased transmissibility has not been conclusively shown but the genomic data is suggestive. The mathematical models can be tweaked to show any result, and don’t take into account founder effects or population-level changes that might be affecting transmission.
  • Spike protein changes are sufficient to require new primers for PCR tests, so they have had to rely on other genes for diagnosis.
  • The spike protein change is NOT enough to alter antibody response. This has been verified in animal models. Existing vaccines will most likely work fine on the new variant.
  • Underdiscussed: the ORF8 deletion may make a less-virulent disease course. (SARS-CoV-1 had one midway through that outbreak with that consequence.) It’s not that the disease is intrinsically more transmissible, but if you don’t feel sick you’re more likely to be out and shedding virus. We do not definitively know this to be the case at this point, however. 
Update 2020-12-29: I wanted to address a point that @politicalmath raised on his recent Substack post on COVID-19 strains; the consensus on TWiV seems to be that the US does much less viral sequencing than they do in the UK, although it’s unknown if what we do is enough to adequately assess spread by particular isolate. In any case, he links to a useful new (to me) site that tracks viral spread, Bookmarked.
Update 2020-12-30: It was pointed out to me on Twitter that the strain is actually called B.1.1.7, which "has an unusually large number of genetic changes, particularly in the spike protein". I'm still not terribly worried about antibody response to this variant, for several reasons:
  1. It's not clear that this has enough difference from other isolates to prevent existing vaccines from mounting an effective immune response.
  2. We have known for months that other (possibly zoonotic) coronaviruses leave antibodies capable of reacting with SARS-CoV-2. It doesn't have to be perfect to work.
  3. If B.1.1.7 is really a major shift, changing the mRNA vaccine to include the new spike protein should be a simple thing that could be turned around rapidly. (Of course, that assumes the FDA will allow an altered vaccine to be delivered without widespread testing first.)

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