Omicron was first reported in South Africa on Nov. 24, 2021, and within mere days it was already making the rounds in the United States, spiking SARS-CoV-2 case numbers as it infiltrated every school, restaurant, and family gathering. But when exactly did omicron unseat the delta variant to become dominant? And how quickly did it actually take over?
These are the questions that a team led by researchers at Harvard Medical School set out to study in real time using a new, faster, variant-determining technique to analyze SARS-CoV-2 samples from screening programs across area universities.
Their analysis, published May 25 in Clinical Infectious Diseases, shows that omicron arrived in Massachusetts earlier than experts predicted, and took over in a matter of days — information that the study authors immediately presented to local hospitals and public health departments to inform preparations for a surge of COVID-19 cases.
“Omicron’s rise to global dominance was extremely rapid, and so was its emergence here in Boston. It moved so fast that we’d have missed a lot of cases if it weren’t for these screening programs run by colleges, but with them we were able to document the takeover,” said Bill Hanage, an associate professor of epidemiology at Harvard T.H. Chan School of Public Health and an author on the paper.
Researchers from Boston University, Harvard University, and Northeastern University collaborated to analyze SARS-CoV-2 samples from their asymptomatic screening programs. They found that omicron accounted for over 90 percent of SARS-CoV-2 infections as early as nine days after it arrived in a community. Moreover, 10 percent of cases in university communities were from omicron up to 10 days before omicron hit the 10 percent mark in Massachusetts.
Omicron outcompeted the delta variant at universities one to two weeks earlier than it did in the state as a whole. Additionally, patients infected with omicron had a lower viral load than those infected with delta — indicating that increased transmission of omicron was due to characteristics of the variant itself, rather than the presence of more virus.
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