CDC: Alpha Variant Continues To Decline In US As Delta & P.1 Rise

 

#16,032

The above graphic shows the rapid rise of the B.1.1.7 (Alpha) variant (light orange) in the United States starting in January, reaching its peak in mid-May, and slowly giving way to the P.1 (Gamma) and B.1.617.2 (Delta) variants in June.  

Yesterday the CDC released their latest surveillance numbers on variant proportions in the United States (see below) as of June 5th, dropping B.1.1.7 down to a 60% share, while P.1 and B.1.617.2 continue to gain. 

These updates are already more than 2 weeks old when we get them, but the CDC added a `Nowcast' option to predict - based on recent trajectories - where the numbers were on June 19th (see below). 

As you can see, B.1.617.2 is expected to have more than doubled (to 20.6%), while P.1. increases 50% to 16.4%.  B.1.1.7 drops to just barely over 50%, and based on these trends, should no longer be dominant by the 4th of July.

This short and dramatic `life cycle' of B.1.1.7 - once thought to be unstoppable - illustrates what happens when viral evolution produces a `better' variant.  Alpha was clearly superior to the `wild-type' COVID of 2020, and and quickly swept the world.

Currently, there are at least two variants (B.1.617.2 & P.1) that can outperform Alpha, and they are poised to dominant - at least - until something more biologically `fit' comes along. 

This pattern of one rising variant upending the last dominant strain is likely to continue for some time.  Not all variants - even those that are destined for dominance - will carry higher virulence.  Just as we see with influenza, some annual flu strains are much worse than others. 

But the pattern we are seeing now, of new variants emerging and jostling for dominance on the world stage, is likely to continue for some time.  

Maybe we get lucky, and an attenuated, more benign, COVID variant supplants these more aggressive strains. Or naturally acquired immunity, or vaccines, diminish their impact.

But in the near-term, at least, any hopes of this pandemic's imminent demise are probably premature. 

The CDC updated their Variant by State table yesterday, adding the Delta Variant.  Curiously, Missouri (based ob a relatively small number of samples) reports the highest percentage (29.1%)  of Delta in the country.

Yesterday the CDC also updated their COVID Variant Classifications and Definitions.

SARS-CoV-2 Variant Classifications and Definitions

Updated June 22, 2021
 
Key Points
  
Genetic variants of SARS-CoV-2 have been emerging and circulating around the world throughout the COVID-19 pandemic.

Viral mutations and variants in the United States are routinely monitored through sequence-based surveillance, laboratory studies, and epidemiological investigations.

A US government interagency group developed a Variant Classification scheme that defines three classes of SARS-CoV-2 variants:

Variant of Interest

Variant of Concern

Variant of High Consequence

The B.1.1.7 (Alpha), B.1.351 (Beta), P.1 (Gamma), B.1.427 (Epsilon), B.1.429 (Epsilon), and B.1.617.2 (Delta) variants circulating in the United States are classified as variants of concern.

To date, no variants of high consequence have been identified in the United States.

Laboratory studies suggest specific monoclonal antibody treatments may be less effective for treating cases of COVID-19 caused by variants with certain substitutions or combinations of substitutions in the spike protein.

• L452R is present in B.1.526.1, B.1.427 (Epsilon), and B.1.429 (Epsilon) lineages, as well as the B.1.617 (Kappa, Delta) lineages and sub-lineages.
• E484K is present in B.1.525 (Eta), P.2 (Zeta), P.1 (Gamma), and B.1.351 (Beta), but only some strains of B.1.526 (Iota) and B.1.1.7 (Alpha).
• The combination of K417N, E484K, and N501Y substitutions is present in B.1.351 (Beta).
• The combination of K417T, E484K, and N501Y substitutions is present in P.1 (Gamma).

Viruses constantly change through mutation. A variant has one or more mutations that differentiate it from other variants in circulation. As expected, multiple variants of SARS-CoV-2 have been documented in the United States and globally throughout this pandemic. To inform local outbreak investigations and understand national trends, scientists compare genetic differences between viruses to identify variants and how they are related to each other.