The coronavirus is spreading faster in Franklin and Essex counties now than ever before.

Since the pandemic began, 4,163 Franklin County residents have tested positive for COVID-19. More than a third of those positive results — 1,298 of them — have been reported within the last two-and-a-half months, according to data released by Franklin County Public Health. The Essex County Health Department has reported 2,282 total cases since the pandemic began. About a quarter of those, 584 cases, were reported within the past two-and-a-half months.

As of Wednesday, there were 161 active cases in Franklin County; as of Tuesday, there were 71 in Essex County.

Franklin County started to see an uptick in cases at the end of August and has experienced “high transmission ongoing since then,” Public Health Director Kathleen Strack said Tuesday.

“People are interacting more closely with each other, which is allowing the disease to spread more easily throughout our communities,” she said.

Another factor could be the higher transmissibility of new variants of the coronavirus. Two recent studies have shown that as the coronavirus mutates, the new variants — such as the Alpha variant — are evolving and becoming more efficient at spreading through the air. One study, conducted by a team of researchers led by National Institute of Allergy and Infectious Diseases virologist Dr. Vincent Munster, showed that those infected with the Alpha variant exhaled much more of the virus into smaller, farther-traveling droplets than those infected with the original virus.

“SARS-CoV-2 is evolving toward more efficient aerosol generation and loose-fitting masks provide significant but only modest source control,” the study reads. “Therefore, until vaccination rates are very high, continued layered controls and tight-fitting masks and respirators will be necessary.”

Unvaccinated people make up the majority of new cases in Franklin County. About 57% of Franklin County residents who have tested positive for COVID-19 since July have been unvaccinated, according to Strack.

Many new cases are among adults, according to Strack. Since July, 17% of cases have been among those who are between the ages of 25 and 34. People between the age of 35 and 44 make up 15% of cases since July.

With the uptick in cases, a higher number of people are being hospitalized with COVID-19. Strack said an average of 12 to 13 people are being hospitalized in Franklin County each week.

The Essex and Franklin County health departments are continuing to recommend much of the same safety measures as they have for the past few months. Strack said FCPH recommends diligence in wearing a mask, socially distancing, staying home when sick, getting vaccinated and washing hands frequently. The department also recommends sanitizing surfaces and reducing the size of gatherings.

As of Wednesday, 65.8% of Essex County residents and 54.7% of Franklin County residents have been at least partially vaccinated, according to the state Department of Health. About 61.6% of Essex County and 50.9% of Franklin County residents have been fully vaccinated.