In a blog post Wednesday, the Boston Public Health Commission said the city's test positivity rate currently sits at 6.2%, which is above the agency's "threshold of concern" of 5%.
It's also nearly three times higher than the 2.2% test positivity rate recorded one month ago.
Additionally, data shows young adults between ages 20 and 30 are driving the increase and have the highest case rate in Boston.
Ahead of several holidays -- including Passover, Easter and Ramadan -- and the 126th running of the Boston Marathon Monday, the BPHC recommended wearing a well-fitting mask, getting tested before attending indoors gatherings, and getting vaccinated or boosted.
"Celebrating with family and friends is an important and treasured time and, as cases increase, we must remain vigilant so we can be together safely," Dr. Bisola Ojikutu, Commissioner of Public Health and Executive Director of the BPHC, said in a statement. "We have the tools … to stay safe and lower the risk of COVID-19 infection and severe illness."
Experts said the increase in Boston is mostly due to the spread of BA.2, a highly infectious subvariant of the original BA.1 omicron variant.
According to data from the Centers for Disease Control and Prevention, BA.2 makes up more than 90% of cases that have undergone genome sequencing in New England.
"It's nothing compared to what we saw in terms of the huge and dramatic spike when BA.1 was in the process of replacing the delta variant," Dr. Shira Doron, an infectious disease physician and hospital epidemiologist at Tufts Medical Center in Boston, told ABC News. "It's an uptick, it's not what we want, but it's much less significant than BA.1."
Dr. Paul Sax, clinical director of the division of infectious diseases at Brigham and Women's Hospital in Boston, said health officials had been preparing for an increase in the city after seeing cases rise in Western Europe due to BA.2 a few weeks ago.
"Whatever happens in Western Europe [with COVID-19] has been a harbinger of what's going to come in the United States," he told ABC News. "You can almost set your calendar by it."
However, there may be some positive signs that this increase in cases will not lead to another wave.
At Tufts Medical Center, Doron said there are more people seeking COVID-19 treatment at outpatient facilities compared to a few weeks ago, but there has not been an increase in hospitalizations.
She added that there has also been a small increase of employees testing positive every day, but it's not causing staffing shortages.
"It's not straining our ability to properly staff, it's not straining our ability to get people in for monoclonal antibodies if they need it," Doron said.
Experts suggested one reason why COVID-19 cases and hospitalizations may not be surging as they did during the winter is because so many people were infected during the omicron wave that they may have boosted their immunity.
"So many people came down with COVID during the last wave ... that they either knew someone who had it, or they had it themselves" Sax said.
Both doctors recommended similar precautions to the BPHC over the holiday weekend including getting tested before gathering with family and friends and taking measures, such as masking indoors, especially if someone is immunocompromised.
Sax also recommended anyone who tests positive for COVID-19 and is experiencing symptoms contact their doctor to see if they're eligible for Paxlovid, Pfizer's antiviral pill.
"Unlike our previous waves, we are lucky enough to have an antiviral treatment," Sax said. "The key is to take it quickly so, as soon as they get diagnosed, they should see if they are eligible because it could really help prevent the most dreaded complications of COVID-19."