Modeling COVID Risks in Classrooms

By Sonia Fernandez, UC Santa Barbara

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

“It’s probably the safest place in the county as far as COVID transmission goes,” said Dr. Scott Grafton, M.D., professor in the Department of Psychological & Brain Sciences and the Campus COVID-19 mitigation program manager.

As with many university campuses across the country, UC Santa Barbara delayed the return of students to in-person instruction after the winter break to deal with logistical issues related to testing, vaccination and possible absences brought on by the omicron variant, which by mid-December become the dominant COVID variant. Now that we know more about the variant’s behavior and its response to vaccines, Grafton said, it’s possible to get a better sense of how protected students would be as they return to classrooms on campus.

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

High Level of Immunity
This bit of positive news is the result of modeling that incorporates the latest scientific knowledge about omicron’s behavior, and data from the state and Santa Barbara County Public Health Department reflecting when the variant arrived and how quickly it spread among vaccinated people. Add to that the success the campus had in fending off classroom transmission during the delta variant wave in the fall session.

“Omicron is different than delta for a number of reasons,” said UCSB chemical engineering professor Todd Squires, who conducted the classroom-level transmission modeling. “It appears to be more transmissible, and it seems to be avoiding the immunity that many of us have.” Indeed, some who are vaccinated have reported breakthrough infections, though those cases are typically milder and of shorter duration than infections in unvaccinated people, who also make up the majority of those infected.

Fortunately the steep rise in local cases seems already to have peaked earlier this month — likely around Jan. 14, according to California state’s ensemble estimate, and seven-day averages of county case rates peaked around Jan. 7.

The seven-day average of COVID-19 case rates peaked around Jan. 7 Photo Credit: TODD SQUIRES

“I think the hard intuition for everyone is to recognize that case rates can’t go up forever,” Grafton said. A virus with high transmission 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 the campus will have gained immunity to omicron via infection.

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

“If we follow the vaccine efficacy 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 really small fraction of campus who are susceptible or could be transmitters, which puts us in a good position.”

Layers of Protection

On the UCSB campus, where vaccination is already high — over 95% — and booster rates will be similarly high by Jan. 31, the community’s collective efforts to protect themselves and others helps significantly. In addition to requiring vaccinations, the campus, since near the beginning 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 lingering virus-laden aerosols by promoting airflow through enclosed spaces.

“Every step you take helps to reduce the likelihood of infection in a multiplicative manner,” 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 jumping from host to host. What virus particles might be lingering in the air can be taken care of with good ventilation, he said.

Individual Risk of Transmission

“We worked very hard to assess transmission risk in all classrooms – which required a detailed look at all ventilation systems – and to identify classrooms that might need a little bit of an extra boost,” said Squires — an expert in fluid mechanics — of efforts undertaken in anticipation of the students’ return to campus last fall. They worked to ensure all air handling units were set to deliver full outside air, and installed portable HEPA filters in instructional spaces that did not have a direct, forced-supply of fresh air, and issued guidance regarding safest-practices regarding doors and windows. 

Campus policy and practice regarding masking, ventilation and vaccination led to no in-class transmission of COVID throughout the fall quarter, even as the wider community underwent the onslaught of the delta variant, which at that time was the most infectious variant. It didn’t mean that no one had COVID — according to Grafton, it meant that even if someone showed up to class with it, the protections in place prevented it from spreading to others in the room.

“There were 89 cases where an individual had COVID and attended class, which worked out to nearly 25,000 exposure events,” Squires said. “Of all of those, there was not one conventional in-person classroom transmission.” One known transmission did occur — during a theater arts rehearsal, involving actors that were unmasked and in prolonged, close physical proximity.

The classroom COVID transmission model allows the researchers to calculate the risk for individuals more precisely, given factors such as the size of the room, the length of time spent in that room, the number of people in the room, the room’s ventilation performance and emerging information on the behavior of the omicron variant. Assuming everyone is boosted and masked, for instance, the number of transmissions predicted in a full Campbell Hall auditorium would be about one for every 50 classes of 50 minutes in duration, and will become less probable each day. 

“For more typical classrooms, that number drops by a factor of 17, or one per 850 lectures,” Grafton said. “For lab-based classes, one per 2,450.”

The classroom transmission rate may be low and the community case rates are expected to drop as sharply as they rose, but, said the researchers, the campus’s success at keeping COVID transmissions low will rely on continued vigilance, compliance, and care.


Written by Anonymous

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  1. LOL, One day, mask mandates will be gone, yet rest assured, there WILL be freaks who have embraced being masked as a way of life…. You know, the people driving in their cars by themselves with masks on, walking along the beach with masks… They will never give it up!

  2. Just got this email from school… pretty good humor!!!!
    Dear Parent/Guardian:
    Santa Barbara County Public Health indicated that the rules with the Omicron variant differ from previous COVID variants, and schools have proven to be a safer place for students than at home or elsewhere. The health and well-being of our students and staff are our top priority. As we continue to provide COVID-19 testing for students and staff this week at school, we are identifying positive cases. Your child may have been exposed to an individual diagnosed with COVID-19. We are following Public Health recommendations to ensure the person with COVID-19 follows instructions for isolation and remains away from others until they can safely return to school.
    What does this mean for you and your child?
    Your child may remain in school unless they develop symptoms or test positive for COVID-19. Being exposed to somebody with COVID-19 does not necessarily mean that your child will become infected. In fact, scientific research, and experience from around the country – including from California during this school year – demonstrate that schools remain among the safest places for children to be.

  3. I wonder why some find this so freaking hard to accept other than political reasons – this was very well stated: ““Every step you take helps to reduce the likelihood of infection in a multiplicative manner,” 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 jumping from host to host. What virus particles might be lingering in the air can be taken care of with good ventilation, he said.”

  4. CHIP – Demanding you put something on your face is not the same as demanding someone take something of their own. For those who chose to wear masks, it’s nothing more than choosing to wear a hat, at least from a 3rd party perspective. How are you (or anyone) harmed or inconvenienced in any way by seeing someone wearing a mask once the mandates have ended? I appreciate your “respect” of those who choose to wear a mask, but it’s not at all the “same courtesy in return.”

  5. 306pm – How so? I said for the whole year that school’s should stay open (as they are throughout the world) because there is no evidence of increased spread when school is in session. I get that there are a lot of posters on here who loudly demanded schools close and stay closed and are now kind of starting to see how silly/wrong that was…I guess it’s OK…not sure why you are going on the attack though.

  6. Sac – As we should have learned over the last two years, the school district rarely said or did the right thing. They did the easiest thing…which was never the best. You and I both loudly railed against school closures…it was a horrible mistake. Truly reprehensible.

  7. Schools are “safer place for students than at home?” Haha, no, not at all. Sure, with precautions, schools are very safe but by no means are they safer than being at home. I have a friend who homeschools now. Guess how many cases of covid they’ve had in their house? Zero. I also know both my kids’ teachers got covid and multiple kids in their classes got it too. How can you say that is safer than avoiding people and staying home? It sure wasn’t safer for those teachers and those kids! Nonsense.

  8. Let me clarify before VOICE starts trolling (I can see he’s already sneaking in here)…..
    I am in NO WAY saying schools aren’t safe or that they never were. I was 100% for return to school back in Fall of 2020. I’m ONLY saying the statement that schools are “safer than at home” cannot be accurate. Just think about it – what is safer: being indoors with a large group of people or being alone with only your family at home? The letter from GUSD must have had a typo. There’s no way on earth that could be factually accurate. BUT…. if there is some study proving me wrong, I’ll happily change my tune. I just don’t think, using common sense, that can be true.

  9. Duke – I was all for it when schools re-opened in SB. I thought they had taken a little too long to get safety protocols in place but none the less gladly sent mine back to school even though we had the option of continuing distance learning. Not sure why you are interested in my family endeavors.

  10. MM – Exactly. My point is only that the blanket statement that “schools are safer than homes” as far as catching covid, is just not true. In some cases yes, but to proclaim they are safer than all homes is wrong. It’s saying you’re more likely to get covid at home than at school where you’re sitting in a classroom with many others, all from different home environments and varying degrees of precaution, and then out playing on the playground or close contact sports at recess, than if you do school at home, alone in your room.
    It’s simply a false statement for the district to put out.

  11. Regarding Demnark: Denmark will offer a fourth coronavirus vaccination to the most vulnerable citizens as it faces record infections from the Omicron variant, the country’s health minister said on Wednesday. Lawmakers agreed to reopen theatres, cinemas, museums, entertainment parks and botanic gardens, and allow limited spectators at indoor and outdoor sports events.
    Last time I checked – we can do all of those things here….

  12. Coastwatch, LOL, one day mask mandates will be gone and people will be allowed to choose whether to continue to wear a mask or not. At that point an entirely personal decision.
    Will it be too much to ask that people be adult/mature about this and respectfully allow another person to choose for themself, especially without name calling??
    Or can this seemingly simple and civil ideal not happen because now…they will never give up!
    Which they will you be…

  13. Sac – They appear to be referring to at home as in “not in school”. More spread is happening outside of school, and more spread happens when school is remote instead of in person. This aligns with data that several of us had been posting since Summer of 2020…that closing schools makes no sense and is in fact a distaster. Our school board knew better though…and chose to ignore logic and science and close it all down.

  14. And there has been countless data of the harm that shutting down schools for a year had. It’s too bad so many people were OK with their public school closing…it shouldn’t have happened as it was obviously a mistake at the time.

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