The first known case of the Omicron COVID-19 variant in Massachusetts has been detected in a woman in her 20s who lives in Middlesex County, public health officials said Saturday, marking a new milestone in the state’s pandemic odyssey as cases have rapidly risen heading into winter.
The woman’s case appears to be one of a “mild disease” and she did not require hospitalization, according to the state Department of Public Health’s statement. The woman is fully vaccinated, the statement said.
The World Health Organization and the US Centers for Disease Control and Prevention have determined the new mutation of the coronavirus a “variant of concern” and the variant has already been reported in about two dozen countries earlier this week.
And while public health experts had been widely anticipating the variant’s arrival in Massachusetts, confirmation of the first case underscored the need for swift action to fight the virus overall, most notably through vaccination and booster shots.
“We shouldn’t be so focused on Omicron but the overall surge across the state and the country and continue working to convince the unvaccinated to get vaccinated, and the vaccinated to get a booster,” said Dr. Daniel Kuritzkes, chief of infectious diseases at Brigham and Women’s Hospital.
“I don’t think there is any reason to be particularly concerned right now that Omicron is some kind of Frankenstein virus that will infect everyone and cause a terrible disease,” he added. “Unfortunately, like everything else we’ve learned [during the pandemic], it takes time to gather information and know for sure how Omicron will behave.”
As of Friday, there were more than 1,000 people hospitalized with COVID-19 in Massachusetts and more than 190 in intensive care units.
More than 19,000 people in Massachusetts have died from COVID-19 since the start of the pandemic.
Others agreed more data must be collected about the variant that was first detected in South Africa to understand its transmissibility and the severity of the disease it may cause.
The variant’s detection in Massachusetts doesn’t change that important research and work that lies ahead, said Dr. Jacob Lemieux, an infectious disease specialist at Massachusetts General Hospital.
“Over the coming days, we need to collect information about how quickly these cases spread and in whom these cases are occurring, and get a better understanding of the consequences for the patients and the public health system,” said Lemieux, who is also the co-leader of the viral variants program at the Massachusetts Consortium on Pathogen Readiness.
Among the most urgent questions to answer is how Omicron might spread in different populations, including different age groups and those with varying rates of vaccinations, he said.
The local concerns come as scientists around the world race to understand many facets of this fast-moving but still somewhat mysterious variant, including whether it produces more severe illness than the Delta strain, and how well COVID vaccines stand up against it.
“In the coming days and weeks we are going to learn a lot, unfortunately, about Omicron,” Lemieux said.
Health experts agreed that it was inevitable the Omicron variant would eventually be discovered here and said it is likely to already have begun to spread beyond the one case that has been detected.
“We have been tracking the variant since before Thanksgiving with our partners in South Africa and coordinating with wastewater treatment sites all over the United States, and the presumption has been it’s just a matter of time before it shows up in most places in the US,” said Samuel Scarpino, managing director of pathogen surveillance at the Rockefeller Foundation’s Pandemic Prevention Institute.
Many of the first cases of Omicron reported in the United States so far have been in people who are fully vaccinated, and Scarpino said that it’s hard to interpret what that might suggest about how well vaccines are protecting people against this new strain of COVD.
“Most of the people traveling tend to be vaccinated so it’s hard to know if we are seeing more breakthrough cases or not,” he said.
A preliminary study published Thursday by scientists in South Africa, which has not been peer-reviewed, found that Omicron is at least three times more likely to cause reinfection than previous variants, such as Delta. Acquired immunity from a previous infection was thought to be helping tamp down infections in countries with low vaccination rates like South Africa.
Scarpino said that as scientists work to sort out so many unknowns, the take-home message is that basic interventions used during the pandemic, such as masks and good ventilation “work really well against Omicron, Delta, Alpha, and the entire stew of variants.”
Scientists have been concerned about the unusual number of mutations in the Omicron variant, and have been working to discover how those mutations have changed the virus. Scientists are still working to determine how Omicron’s transmissibility and disease severity compares with the predominant Delta variant, the Department of Public Health’s statement said. Delta accounts for nearly 100 percent of US cases and continues to cause illnesses and deaths at a high rate.
“There is some limited evidence that Omicron could be more transmissible than other COVID-19 virus variants, including Delta,” the statement said, which also noted that the variant is being monitored closely by public health authorities around the world.
The WHO has said it is looking into what its impact is on “existing countermeasures” such as vaccines, though information is limited.
The Massachusetts case was identified through genetic sequencing performed at Ipswich-based New England Biolabs, the statement said.
Officials said all three COVID-19 vaccines in use in the United States have shown to be “highly protective” against severe disease resulting in hospitalization or death from the known variants. The vaccine remains the single best way for people to protect themselves, their loved ones, and their community from the virus, the statement said.
There are more than 1,000 locations across the state where people can get a free vaccine or booster shot, with no identification or insurance needed, the statement said.
State officials said that people can help stop the spread of COVID-19 by getting tested and staying home if they are sick, following masking requirements, and by frequently washing their hands or using hand sanitizer. People should also tell close contacts if they test positive for COVID-19 so they can take appropriate steps, the statement said.
A former infectious disease specialist at Boston Medical Center said vaccinations and other safety measures are essential to help protect people from the new variant.
“If you’ve been taking the general precautions — wearing a mask when indoors, limiting the size of the number of people you’re hanging out with, and making sure that you’re optimally vaccinated — then your behaviors don’t need to change, at least not at this moment,” said Dr. Joshua Barocas, an associate professor of medicine at the University of Colorado, where he relocated last summer. “That’s why it’s called a ‘variant of concern’ and not a ‘variant of certain death.’ ”
Martin Finucane of the Globe staff contributed to this report.
John Hilliard can be reached at email@example.com. Kay Lazar can be reached at firstname.lastname@example.org Follow her on Twitter @GlobeKayLazar. Nick Stoico can be reached at email@example.com. Follow him on Twitter @NickStoico.