Here's how one college system kept Covid-19 cases down as they surged throughout the state

A mobile testing lab earlier this year at the University of Maine. As tens of thousands of students returned to residence halls and into full classrooms, university leaders hoped the measures they put in place would keep Covid-19 cases down.

(CNN)Students began flocking back to the six campuses of the University of Maine this fall hoping for a more normal college experience, one without shutdowns or Zoom classes.

As those tens of thousands of students returned to residence halls and full classrooms, university leaders hoped the measures they put in place would keep Covid-19 cases down and avoid widespread cases that shut down many campuses nationwide last spring.
University of Maine President Joan Ferrini-Mundy, who chairs the system's Science Advisory Board, told CNN they prepared a science-based, multifaceted approach with the help of a team that included an epidemiologist, a statistician, microbiologists and virologists.
    As the semester began at the end of August, university officials were about to find out if it would work.
      In September, cases in the heavily vaccinated state began to rise. Hospitals began filling up with numbers not seen since a surge in January, according to the state's Center for Disease Control & Prevention. The number of people needing ventilators reached all-time highs and intensive care units reached record numbers, according to state health data. All counties began to be classified as having high levels of transmission.
        An inside view of ICU nurses caring for unvaccinated Covid-19 patients at the Maine Medical Center.
        And yet, throughout the University of Maine, cases remained extremely low and seemingly avoided the crush taking hold of the state. At the start of October, the campus system of more than 30,000 students and employees had a 1.5% positivity rate, compared to the state's rising 4.5% positivity rate.
        The university told CNN that the system has had 52 known Covid-19 cases among students or employees as of Wednesday. Forty-five of those were on the flagship campus in Orono. Zero cases were recorded at the University of Maine at Augusta, University of Maine Farmington and University of Maine at Presque Isle campuses.
          So how did they do it?
          Ferrini-Mundy credits that multifront system -- known as the "Swiss cheese" model -- as a key defense against Covid-19. While each prevention measure, or layer of cheese has holes in it, when stacked together they create an effective defense.
          Ferrini-Mundy knows a big part of it is not just the measures the campus put in place, but the willingness to adhere -- a situation that doesn't always exist in other settings.
          University of Maine President Joan Ferrini-Mundy also chairs the system's Science Advisory Board, which helped inform mitigation measures.
          "We've been able to control this through excellent behavior and compliance by our students," Ferrini-Mundy said.
          Lucia Mullen, a senior analyst at Johns Hopkins Center for Health Security, said the university's success shows two things. First, that this "Swiss cheese" model is the strongest plan to increase activities and social interactions while making sure transmission is low.
          "It also shows the difference like compliance and willingness can make in in bringing down cases," Mullen said.
          While there is always going to be exceptions and settings where the university model couldn't work, Mullen says it's a good example of success in a time of Covid-19 fatigue.

          Vaccination efforts

          One of the big reasons for the university system success is the rate of vaccination on campus compared with the rest of the state. Maine has a strong full dose vaccination rate of 74.4%, compared to the university's systemwide 88.3%.
          But, state health officials have said in briefings, the Delta variant only needs a small window to create havoc. And that's mainly what happened among the unvaccinated population, according to Maine CDC Director Dr. Nirav D. Shah. Some pockets, especially rural areas, don't have vaccination rates on par with the state's average.
          Senior citizens leave a vaccination site at a former department store in Sanford.
          "Folks are getting it in their day-to-day lives," Shah said in video message responding to the uptick in cases. "Maybe because they had coffee with a friend or had dinner with some friends at their house in smaller settings where the virus can travel easily from person to person. Right now, most of the new cases of Covid-19 that we are seeing are happening among unvaccinated people."
          On the University of Maine campuses, a vaccine mandate seems to have helped protect students against the community transmission seen in the rest of the state. More and more students got vaccinated early in the semester, giving the campus a measure of protection, the university said.
          As of Tuesday, 97.2% of residential students were in compliance. Across the system, including faculty, staff, and students off-campus that rate is 88.3%, according to Ferrini-Mundy. The mandat