Local modeling

Modeling COVID Risks in Classrooms

By Sonia Fernandez, UC Santa Barbara

The local omicron surge has peaked, infections are down, and the campus pandemic protocols that have been in place since last summer have proven very effective, raising reasonable expectations for a safe return to classes. in person at UC Santa Barbara at the end of the month.

“It’s probably the safest place in the county for COVID transmission,” said Dr. Scott Grafton, MD, professor in the Department of Psychological and Brain Sciences and manager of the COVID-19 Mitigation Program. 19 on campus.

As with many college campuses across the country, UC Santa Barbara delayed the return of students to in-person instruction after winter break to deal with logistical issues related to testing, vaccinations and possible absences caused by the omicron variant, which in mid-December became the dominant COVID variant. Now that we know more about the behavior of the variant and its response to vaccines, Grafton said, it’s possible to get a better idea of ​​how well students are protected when they return to classrooms on campus.

“Looking forward, we see that by January 31, up to 90% of campus will be immune to omicron because they have had it or are protected by vaccines,” Grafton said. . “Stop and think about what this means for the campus as a whole. The risk of transmission of the omicron becomes very low if there are so few people to give it or to obtain it.

High level of immunity
This positive news is the result of modeling that incorporates the latest scientific insights into omicron’s behavior, as well as data from the Santa Barbara State and County Public Health Department showing when the variant arrived and at how quickly it spread among vaccinated people. Add to that the success of the campus in pushing back in-class transmission during the delta variant wave of the fall semester.

“Omicron is different from delta for a number of reasons,” said Todd Squires, a UCSB professor of chemical engineering who led the class-level transmission modeling. “It seems to be more transmissible, and it seems to stave off the immunity that a lot of us have.” Indeed, some vaccinated people have reported breakthrough infections, although these cases are generally milder and of shorter duration than infections in unvaccinated people, who also make up the majority of those infected.

Fortunately, the sharp rise in local cases already appears to have peaked earlier this month — likely around January 14, according to California’s statewide estimate, and seven-day averages of case rates from counties peaked around January 7.

The seven-day average of COVID-19 case rates peaked around January 7 Photo credit: TODD SQUIRES

“I think the hard hunch for everyone is to recognize that case rates can’t go up forever,” Grafton said. A high-transmission virus like this variant is going to run out of people to infect, he explained. By the end of the month, the researchers estimate that up to 40% of campus will have acquired immunity to omicron through infection.

Meanwhile, recent studies published in the Journal of the American Medical Association and by the Centers for Disease Control and Prevention highlight the importance of vaccinations and booster shots: according to these studies, vaccinated people are less likely to contract infections due to omicron than unvaccinated people. And because immunity to COVID wanes over time, those with booster shots receive even more protection than from vaccination alone, making vaccination plus a booster the surest way to get good protection against the variant.

“If we follow the vaccine effectiveness information we have for omicron, it looks like about half the campus is immune because their vaccine is still working,” Grafton said. “That leaves a very small fraction of the campus that is susceptible or could be a transmitter, which puts us in a good position.”

Layers of protection

On the UCSB campus, where vaccination is already high – over 95% – and recall rates will be just as high by January 31, the community’s collective efforts to protect themselves and others are helping in a significative way. In addition to requiring vaccinations, the campus, since the start of the pandemic, has implemented safety measures, including masking, social distancing and hand hygiene, in addition to regular testing and strategies to reduce or eliminate any persistent virus-laden aerosols by promoting air circulation through closed spaces.

“Every step you take helps reduce the risk of infection in a multiplicative way,” Squires said. Immunity reduces the chances of catching and carrying the COVID virus, while social distancing and masks further reduce transmission by preventing it from passing from host to host. Virus particles that might linger in the air can be taken care of with good ventilation, he said.

Individual risk of transmission

“We worked very hard to assess the risk of transmission in all classrooms – which required a detailed examination of all ventilation systems – and to identify classrooms that might need a little help. extra,” said Squires — an expert in fluid mechanics — of the efforts undertaken in anticipation of students returning to campus last fall. They worked to ensure all air-handling units were set to provide full outside air, and installed portable HEPA filters in teaching spaces that did not have direct power and forced fresh air, and have issued guidelines for the safest practices for doors and windows.

Campus policy and practices regarding masking, ventilating, and vaccinating led to no transmission of COVID in the classroom throughout the fall term, even as the wider community came under the onslaught of the delta variant, which at the time was the most infectious variant. That didn’t mean no one had COVID — according to Grafton, it meant that even if someone showed up to class with it, the safeguards in place prevented it from spreading to others in the room.

“There were 89 instances where someone had COVID and attended a class, which amounted to almost 25,000 exposure events,” Squires said. “Of all of these, there was not a single conventional in-person classroom transmission.” One known transmission occurred – during a theater arts rehearsal, involving unmasked actors and in prolonged and close physical proximity.

The classroom COVID transmission model allows researchers to more accurately calculate the risk to individuals, given factors such as room size, time spent in that room, number of people in the room, performance of room breakdown and information about the behavior of the omicron variant. Assuming everyone is boosted and masked, for example, the number of transmissions expected in a full Campbell Hall auditorium would be about one for every 50 50-minute classes and will become less likely each day.

“For more typical classrooms, that number drops by a factor of 17, or one for every 850 classes,” Grafton said. “For lab courses, one for 2,450.”

The classroom transmission rate may be low and community case rates are expected to fall as sharply as they have risen, but, the researchers said, the campus’ success in keeping COVID transmissions low will hinge on a vigilance, compliance and ongoing care.