The Delta variant of the coronavirus has overtaken others in the United States and now represents more than 99 percent of cases tracked in the country, according to the latest biweekly report of sequencing data by the Centers for Disease Control and Prevention.
The variant is the same that was linked to surges of infections in Britain and India this spring and summer, with outbreaks resurfacing after cases had seemed to be on the decline. The Delta variant has been fueling outbreaks in the U.S. through this summer as well, as many people resisted getting the Covid-19 vaccine.
The latest numbers underscore the transmissibility of the variant, as it climbed from just over a quarter of cases by mid-June to near total dominance in September.
“It’s not unexpected, because it’s more transmissible, but it is also a strong reminder that we need to have continuous vigilance,” said Dr. Saskia Popescu, an epidemiologist and assistant professor at George Mason University.
The C.D.C.’s COVID Data Tracker, reporting results for the two-week period ending on Sept. 11, put the B.1.617.2 lineage of Delta at 99.4 percent among variants of concern, with two other Delta lineages tracked at 0.2 percent and 0.1 percent, the Mu variant at 0.1 percent and several other, unidentified variants at 0.2 percent, all for the same period. The results are based on thousands of sequences provided every week through the C.D.C.’s national genomic surveillance efforts, the agency website says.
The country recently experienced a rise in hospitalizations despite the availability of vaccines, and the Delta variant was cited as the culprit in the virus’s advance.
“We’re seeing more children in the hospital now because the Delta variant is more readily transmissible among everybody, adults and children,” Dr. Anthony S. Fauci, the nation’s top infectious disease doctor, told The New York Times.
Popescu said the rise of Delta should help Americans and health officials realize the coronavirus remains a serious public health threat.
“The biggest piece is, ‘Don’t let your guard down.’ We need continuous surveillance, genomic sequencing, access to testing and public health interventions,” Popescu said.
Vaccination and wearing masks can help, she said.
“We have transmission occurring with very limited exposure, and that means that, for example, times without a mask, when you are out and around others, become much more of a risk,” Popescu said.