CDC NOWCAST Estimate as of July 3rd
#16,053
Yesterday afternoon the CDC updated their bi-weekly COVID Variant Proportions surveillance page, which tripled the incidence of the Delta virus in the United States between June 5th (10.1%) and June 19th (30.4%), moving it into second place behind Alpha (B.1.1.7)
These numbers are, obviously, more than two-weeks old, and given the rate of expansion of Delta over the previous 2-week period, it is an easy assumption that Delta has now eclipsed Alpha in the United States.
The CDC saves us that trouble, as they introduced a `Nowcast' option in May that extrapolates - based on recent trends - the estimated percentage of each variant as of the end of latest week. In this case, as of July 3rd, Delta has gained a > 50% share, and Alpha - after a reign of 4 months - is no longer dominant.
This transition from Alpha to Delta has been discussed for weeks (see CDC: Delta Variant Rapidly Gaining Ground In the United States), and comes as no surprise. That said, the speed in which it has done so here (and the UK, Denmark, and other countries) is impressive.
Four months ago, the juggernaut that was Alpha seemed insurmountable. Today it is on the decline globally. How long Delta will stay on top is unknown, but this is a reminder of how quickly the pandemic landscape can change.
Exactly what Delta's dominance will mean to the United States remains uncertain, although the recent rise in cases in the UK (see PHE Graph below) - which is several weeks ahead of us in dealing with the Delta variant - may provide some clues (see UK: PM Statement On Plans To Abandon COVID Restrictions On July 19th).
The CDC sums up what we know about the Delta variant (and its two siblings, AY.1 and AY.2) in the following graphic.
Although we've seen some conflicting reports, the mRNA vaccines appear to offer moderate- to-good protection against symptomatic illness with the Delta variant. We arguably have the best information on the Delta variant from the UK, where it is now comprises > 95% of all COVID cases. Their latest risk assessment (June 25th) reads:
Although US daily case totals are near their lows for the past year, they have been trending up the past couple of weeks. There are concerns that the slowdown in vaccine uptake - combined with the rise in Delta and community events over the 4th of July - could see cases here begin to climb even higher over the summer.
Where all of this leaves us this fall and winter is anyone's guess. But as long as SARS-CoV-2 continues to churn out new, and more transmissible variants, we are going to have to deal with the COVID crisis.
Stay tuned.
