The once dreaded Alpha variant falls quickly – Delta and Gamma take over

Enlarge / People line up outside the Bridge Park Community Leisure Center to receive COVID-19 vaccines in Brent, northwest London on June 19, 2021. A new wave of coronavirus infections is ‘definitely underway’ in England due to the Delta variant first identified in India, a UK government scientist advisory said on Saturday.

Two dreaded variants of the coronavirus are quickly overthrowing America’s most dreaded variant. Their rise has raised concerns among experts that the country will experience continued epidemics and resurgences of COVID-19 unless the current slow pace of vaccination accelerates.

Alpha, the variant formerly known as B.1.1.7 and first identified in the UK, swept across the country earlier this year. It is estimated to be around 50% more transmissible than the version of the pandemic coronavirus, SARS-CoV-2, which spread to Wuhan, China in 2020. The increase in Alpha in the UK l he fall was linked to an increase in cases as the variant virus quickly made up over 90 percent of cases there. Likewise, in the United States, Alpha has emerged as the predominant strain within a few months this year and accounted for about 70 percent of the strains in circulation at the end of April.

But according to fresh data, two other variants now threaten Alpha’s reign in the United States: Delta (alias B.1.617.2, first detected in India) and Gamma (alias P.1, first detected in Brazil and Japan). Delta is considered the most worrying variant ever. While vaccines are still effective against Delta, the variant is estimated to be 50-60% more contagious than Alpha, and evidence suggests it can cause more serious illness. When Delta first appeared in the UK in early April, it quickly overcame Alpha and now accounts for around 90% of cases. Gamma, on the other hand, does not spread so quickly, but it slightly reduces the effectiveness of vaccines.

According to data released online Monday on a preprint server, Delta and Gamma are wasting no time collectively overtaking Alpha in the United States, which has already fallen from dominance. Alpha fell from 70% of cases in April to its current low of around 35 percent. In the preprint study, Delta and Gamma collectively accounted for about 30% of all cases in the United States as of June 9, with Delta accounting for about 14% of cases and Gamma for about 16%.

Data from the Centers for Disease Control and Prevention presented at a White House press conference Tuesday estimates that as of June 19, the share of Delta cases nationwide has now reached 20.6 percent.

Graphic showing the rise of the Delta variant in the UK.
Enlarge / Graphic showing the rise of the Delta variant in the UK.

The preprint study, which was not peer reviewed, was conducted by California researchers at genomics company Helix. The company is working with the CDC to help monitor SARS-CoV-2 variants. Helix researchers had data on nearly 244,000 SARS-CoV-2 positive samples collected since January 2021. And they had the genetic sequences of nearly 20,000 virus isolates collected from 747 counties nationwide since April.

The study has limitations, notably the smaller number of samples collected in recent weeks given a welcome slowdown in transmission. Although the authors suggest that their data set should not be biased in favor of a specific variant, they note that the samples “do not proportionately represent the different regions of the United States by population.” About 25 percent of the samples were collected in Florida, for example. However, when they did the analyzes, they could still see trends nationwide.

Overall, the data clearly indicates that Delta and Gamma are taking over. And Delta in particular is spreading the fastest. It overtakes Gamma and is on its way to becoming the predominant variant in the US, like the UK.

Still, both variants have advantages. When the researchers examined how the two variants spread across various counties, they found that:

The growth curve of [Delta], which is more transmissible but against which vaccines are highly effective, shows faster growth in counties with lower vaccination rates. On the other hand, [Gamma], which is less transmissible but against which vaccines are somewhat less effective, has a higher prevalence in countries with higher vaccination rates.

The data supports experts’ calls for people to get vaccinated and for those vaccinated to stay vigilant. At the White House press conference on Tuesday, leading infectious disease expert Anthony Fauci echoed this concern, calling Delta the “greatest threat” to the country’s exit from the pandemic.

Graph showing the share of Delta cases in the United States
Enlarge / Graph showing the share of Delta cases in the United States

Fauci noted that 34 states have vaccinated less than 70% of their adult populations. There is a “real danger,” Fauci said, that the Delta variant could lead to local increases in COVID-19 cases in the fall in places with low vaccination rates.

“Conclusion: we have the tools,” he said, referring to effective vaccines, “so let’s use them and crush the epidemic. “

About Clara Barnard

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