Graphs show where the Delta variant is surging fastest in the US, with huge spikes in Missouri, Colorado, Utah, and Arkansas

• The number of people infected with the Delta variant has sky-rocketed in four US states, a virus expert said.
• Delta was now the most common virus strain in Missouri, Utah, Colorado, and Arkansas, Trevor Bedford said.
• Bedford co-developed Nextstrain, a data platform used by the World Health Organization that tracks virus outbreaks.

The number of people infected with the highly infectious Delta has skyrocketed in four US states, according to an expert in virus sequencing.

Trevor Bedford, affiliate associate professor at the department of genome sciences at University of Washington, said on Twitter on Thursday that the Delta variant had displaced the formerly-dominant Alpha variant in Missouri, Utah, Colorado, and Arkansas.

-Trevor Bedford (@trvrb) June 30, 2021

Bedford did not say where he got the data from, but he co-developed Nextstrain, a data platform used by the World Health Organization, that tracks virus outbreaks using publicly available data including from the Global Initiative on Sharing All Influenza Data.

The most striking change was in Missouri, where the Alpha variant caused more than 80% of cases in May, and now accounts for about 10% of cases. Meanwhile, the Delta caused about 30% of sequenced cases in May, and more than 80% of new cases now, he said.

Missouri has one of the lowest vaccination rates in the US - 36% of Missourians are fully vaccinated, according to Johns Hopkins University.

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The Delta variant is estimated to be at least twice as infectious as the Alpha variant and has rapidly spread to more than 96 countries. The World Health Organization said in a report released Tuesday that it expected Delta to outcompete other variants worldwide.

Bedford said on June 22 that it was difficult to predict the size of the Delta epidemic, but that he expected it to vary depending on the number of people vaccinated in an area. Real-world data from the UK showed that one dose of Pfizer's vaccine was just 33% protective against COVID-19 with symptoms caused by Delta, rising to 88% effective after two doses.

Bedford did not immediately respond to a request for comment about the source of the data.