Global Spread of B.1.617.2 (Delta) Variant - Credit CDC
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While the B.1.1.7 (Alpha) Variant continues to ride high as the dominant variant in the United States, two other variants (P.1. or ` Gamma' and B.1.617.2 or `Delta') are starting to cut away at its lead.
This week - for the first time - the CDC is reporting a slightly `reduced share' by the Alpha variant, dropping from 69.9% to 69.2% since their last bi-weekly reported.
The P.1 (Gamma) variant currently accounts for just over 8% of the nation's COVID cases, while B.1.617.2 (Delta) is tied for 5th place with just 2.5%. But the Delta variant's rate of growth is roughly 3 times higher than any of the other variants on the board, suggesting it will likely move up in the ranks quickly over the summer.
Some excerpts from the CDC's latest report:
Estimated Proportions of SARS-CoV-2 Lineages
The data below show the estimated biweekly proportions of the most common SARS-CoV-2 lineages circulating in the United States, based on greater than 175,000 sequences collected through CDC’s national genomic surveillance since Dec 20, 2020 and grouped in 2-week intervals. Data are subject to change over time and will be updated as more data become available. Variant proportions are adjusted using statistical weighting to correct for the non-random sampling of sequencing data over time and across states and to provide more representative national estimates.
Nowcast weighted estimates that predict proportions for more recent time intervals are added when “Nowcast On” is selected in the dashboard controls below.
Illustrating how quickly the status quo can change - in the UK, where eight weeks ago the B.1.1.7 variant accounted for more than 95% of all COVID cases - last week the B.1.617.2 variant officially became the dominant strain.
While not yet labeled a VOC by the CDC, the UK and WHO have both declared B.1.617.2 a Variant of Concern.
Late last week, the PHE published a new revised risk assessment on the Delta variant, which once again raised the ante on increased transmissibility, infection severity, and reduced vaccine effectiveness - albeit in the case of increased severity, with low confidence levels.
Changes from the previous week include raising the confidence level from MODERATE to HIGH on reduced vaccine effectiveness, and raising Infection Severity from Not Enough Data to LOW confidence. The overall assessment now reads:
Delta is predominant and all analyses find that it has a very substantial growth advantage. The observed high growth rate is most likely to be due to a combination of place based context, transmissibility and immune escape. Both English and Scottish analyses continue to support the finding of reduced vaccine effectiveness which has increased to high confidence.
New early data from England and Scotland suggest a possible increased risk of hospitalisation compared to Alpha. The priority investigations are vaccine effectiveness against hospitalisation and transmission, household secondary attack rate corrected for vaccination, characterisation of the generation time, viral load and period of infectivity, and epidemiological studies of reinfections.
While there is still considerable debate over how much of a threat the Delta variant poses to fully vaccinated individuals - for those who eschew (or are unable to get) the vaccine - the expected spread of B.1.617.2 may very well represent a serious challenge.
Even assuming the Delta variant proves to be more resistant to the vaccine, there is growing evidence that the vaccine can reduce the severity of a `breakthrough' infections.
Vaccination Makes Illness Milder, Shorter for the Few Vaccinated People Who Do Get COVID-19Press ReleaseFor Immediate Release: Monday, June 7, 2021
