College re-openings could cause 3,200 extra cases of COVID-19 per day in the US

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With the approaching fall of 2020, numerous US colleges made ready to welcome back their students after one missed semester. Many rapidly switched to online classes once an outbreak occurred on campus. Thus, many scientists have begun to question whether in-person instruction should be resumed until the pandemic is well on its way out. A new report published in the preprint server medRxiv* in September 2020 shows the close relationship between the re-opening of colleges, especially those drawing students from high-incidence areas, and those offering in-person instruction, and the significant increase in the incidence of COVID-19 among students and the community.

Does Reopening Cause More Cases?

The current lack of experimental support for this conclusion motivated the current study to look at the occurrence of spillovers from colleges into the surrounding community. The researchers tested the assumption that colleges serving students from high-incidence areas would have higher increases in campus COVID-19 incidence. The highest increase would be in colleges where in-person classes had begun.

Mapping schools and counties. Top panel: US map with counties and schools. Bottom panel School classifications

Mapping schools and counties. Top panel: US map with counties and schools. Bottom panel School classifications

Increased Visitors in the Week Before Classes Started

The researchers sampled all 779 US counties with college campuses for a total of about 1,400 campuses, between July 15th to September 13th, 2020. They found that in the week just before classes began, there was a surge in the number of devices on campus, which continued after the start of classes. The number of devices went up by 47% in the two weeks after classes began compared to the preceding two weeks.

For colleges that had in-person classes, the increase was about 56% compared to 33% for those that offered online classes. Therefore, college re-opening was linked to a rise in incidence by an extra 17 cases per 1,000,000 people. The rise is mainly associated with those that offer in-person classes, at 24 more cases per 1,000,000 people. Institutions that offered only online classes were not found to be associated with any higher risk.

Extra Cases with Out-of-County Exposure

Any campus in which the exposure to infection in students from other counties was increased by 10% was associated with ~12 extra cases per 1,000,000 people. Incorporating other interactions due to in-person instruction, this 10% increase in exposure to people from outside the county is linked to an additional 14 cases per 1,000,000 in counties where the first school began with in-person classes. In other counties, there was no such observed association.

Using Other Measures

When other measures were used, such as the number of new cases over the previous three days in order to rule out a weekend-related surge in cases, new cases over a week and the daily reproduction number, Rt, re-opening is found to be the parameter consistently associated with increased viral transmission. The association with the mode of instruction is no longer significant at this point.

Again, when the county-related transmission rates are adjusted for population size, there was no significant difference whichever mode of instruction was used. However, with this adjustment, re-opening was also no longer associated with the re-opening of colleges.

High-Incidence Home Counties Linked to Higher Cases in College Counties

Still, colleges that served students from high-incidence areas continued to be associated with a higher county incidence of COVID-19 after re-opening. When the number of hours of in-person instruction were factored in for greater detail, they found that the number of new cases is related to the proportion of in-person teaching. Thus, those that had only online or only in-person teaching were predicted to have fewer visitors than those with mostly in-person or with hybrid models of instruction.

The study thus indicates a significant increase in the number of cellular devices visiting the campus in the week before classes start, whichever mode of instruction is used. Secondly, in-person instruction significantly boosts daily new case numbers in the county where the college is located. Moreover, if the county of origin of the student has a high daily incidence, it significantly affects the daily new case number of the county where the college is located. This agrees with the finding that the Rt of the county rises steadily in about 2 weeks from the increase in mobility associated with re-opening.

Is the Increased Incidence due to Imported Cases?

The researchers admit their inability to assess imported cases due to student arrivals on campus from those occurring due to local or community transmission in the county where the college is located. Asymptomatic cases arriving on campus can be captured only by widespread testing on campus.

Nonetheless, it is unlikely that most cases are due to students with COVID-19 arriving at college in large numbers, as this would lead to an increase in cases in the first week of re-opening (based on the assumption that a person tests positive 9 days from infection, on average). This is not borne out by the increase in cases, therefore the Rt, in the second week of classes.

The researchers did not assess the spillover infections in the communities around the campuses since these will take a more extended period to manifest. This would also require more incidence data to be acquired from college campuses. However, the findings indicate the urgency of further evaluating the level of efficacy of countermeasures taken by colleges so far, especially in response to the rapid increase in cases following re-opening.

Implications and Future Directions

The paper thus suggests that college campus re-opening is associated with 3,200 extra cases of COVID-19 every day in the US. This is based on the assumption that these results embrace both new cases on campus and those at home.

The authors describe their conclusions to be “critical” in devising appropriate public health strategies to deal with the transmission in the special context of colleges “as they consider additional strategies to mitigate disease burden and decrease transmission.” Such measures should include paying more attention not just to those communities surrounding the college but those from which the college’s students are drawn.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

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