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Charts: Here’s how the worrisome delta variant is growing in the US

A coronavirus shot being prepared. Officials say the rise of the delta variant underlines the need for everyone to get vaccinated.Craig F. Walker/Globe Staff

Experts and public officials from President Biden on down are warning of the spread of the super-contagious delta variant in the United States, while urging people to step up to get their vaccinations and protect themselves and others.

Dr. Anthony Fauci, the nation’s top infectious disease expert, said at a White House media briefing Tuesday that the variant was “the greatest threat” to eliminating COVID-19 in the United States.

Fauci said that in addition to being more transmissible, the virus was associated with greater disease severity as reflected by the increased risk of hospitalization among those infected.


How do we know the variant is on the rise? Genomic surveillance testing is finding that an increasing proportion of infected people have contracted the delta variant, or B.1.617.2 variant, rather than the alpha variant, or B.1.1.7 variant, which is, at least for now, the predominant variant.

Here’s a chart that shows the growth in the estimated proportion of coronavirus cases caused by the B.1.617.2 variant since the two weeks ending May 8.

Fauci noted that the proportion appeared to be doubling about every two weeks and that the United States appeared to be headed on the same track as the United Kingdom, where the delta variant has grown to account for more than 95 percent of cases — and cases, hospitalizations, and deaths have recently increased.

Here’s a different look at the rise of the B.1.617.2 variant, which shows it gaining ground at the same time the proportion of the B.1.1.7 variant is falling.

The US Centers for Disease Control and Prevention also breaks down its estimates of variant proportions by the 10 US Department of Health and Human Services regions. Region 1, which comprises the New England states, had an estimated delta variant proportion in 17.7 percent of cases in the two weeks ending June 19.


The region is about in the middle of the pack. The regions where the delta variant has made the most inroads are Region 8 (Colorado, Montana, North Dakota, South Dakota, Utah, and Wyoming), where the variant was at 46.4 percent, and Region 7 (Iowa, Kansas, Missouri, and Nebraska) where the variant was at 47.5 percent.

Here is a map showing the proportion of the fading alpha variant and the rising delta variant by state and by region. Click on the dropdown box to switch between the two variants. A table showing the regional results follows.

Experts say the variant is unlikely to pose much risk to the fully vaccinated. They’re concerned about outbreaks in areas where vaccination levels are low and about the impact in young people who have lower levels of vaccine participation. Fauci said a study had found that “youth were driving the UK surge.”

“If there’s a persistence of a recalcitrant group that doesn’t get vaccinated, there will be local type of regional spikes and outbreaks,” Fauci said at the briefing. He added that if people who have not yet been vaccinated get their shots, future spikes are “totally and completely avoidable.”

Material from Globe wire services was used in this report.

Martin Finucane can be reached at martin.finucane@globe.com.