Assessing COVID-19 Prevention Strategies to Permit the Safe Opening of Residential Colleges in Fall 2021

Abstract

Background: Effective vaccines, improved testing technologies, and decreases in COVID-19 incidence prompt an examination of the choices available to residential college administrators seeking to safely resume in-person campus activities in fall 2021.

Objective: To help college administrators design and evaluate customized COVID-19 safety plans.

Design: Decision analysis using a compartmental epidemic model to optimize vaccination, testing, and other nonpharmaceutical interventions depending on decision makers' preferences, choices, and assumptions about epidemic severity and vaccine effectiveness against infection, transmission, and disease progression.

Setting: U.S. residential colleges.

Participants: Hypothetical cohort of 5000 persons (students, faculty, and staff) living and working in close proximity on campus.

Measurements: Cumulative infections over a 120-day semester.

Results: Under base-case assumptions, if 90% coverage can be attained with a vaccine that is 85% protective against infection and 25% protective against asymptomatic transmission, the model finds that campus activities can be resumed while holding cumulative cases below 5% of the population without the need for routine, asymptomatic testing. With 50% population coverage using such a vaccine, a similar cap on cumulative cases would require either daily asymptomatic testing of unvaccinated persons or a combination of less frequent testing and resumption of aggressive distancing and other nonpharmaceutical prevention policies. Colleges returning to pre-COVID-19 campus activities without either broad vaccination coverage or high-frequency testing put their campus population at risk for widespread viral transmission.

Limitation: Uncertainty in data, particularly vaccine effectiveness (preventive and transmission); no distinguishing between students and employees; and assumes limited community intermixing.

Conclusion: Vaccination coverage is the most powerful tool available to residential college administrators seeking to achieve a safe return to prepandemic operations this fall. Given the breadth of potential outcomes in the face of uncontrollable and uncertain factors, even colleges with high vaccination rates should be prepared to reinstitute or expand testing and distancing policies on short notice.

Primary funding source: National Institute on Drug Abuse.

Visual Abstract.. Assessing COVID-19 Prevention Strategies to Allow Colleges to Open in Fall.

This article presents a decision framework and companion tool linked to a standard, dynamic state-transition model of SARS-CoV-2 transmission on campus to help residential college administrators make decisions about vaccination programs and policies, infection surveillance with varying frequencies of testing and target populations, and use of nonpharmaceutical interventions (for example, distancing and masking), all considered with the goal of returning to pre–COVID-19 operations for the fall 2021 semester.

Figure 1.. Cumulative infections with 50% vaccination coverage and testing targeted to the unvaccinated population alone.

The figure illustrates the findings of the model under baseline input data assumptions, assuming 50% vaccination coverage. The curves report the expected cumulative infections in the population over a 120-day semester (y-axis) under alternative frequencies of routine, asymptomatic testing of unvaccinated persons (ranging from no testing to testing every day). The R* is inversely related to the aggressiveness of NPI measures, such as masking and distancing. In the absence of any testing (purple curve), cumulative infections may be held below 5% of the campus population (horizontal red dashed line) if R* is < 1.5 (that is, implementation of aggressive NPIs). With testing twice a week (yellow curve), that level of cumulative infections could be achieved at R* values of < 3.5; with daily testing (blue curve), it could be achieved at R* values of < 5.25. NPI = nonpharmaceutical intervention; R* = on-campus, effective reproduction number.

Figure 2.. Cumulative infections with 70% vaccination coverage and testing targeted to the unvaccinated population alone.

The figure illustrates the findings of the model under baseline input data assumptions, assuming 70% vaccination coverage. The curves report the expected cumulative infections in the population over a 120-day semester (y-axis) under alternative frequencies of routine, asymptomatic testing of unvaccinated persons (ranging from no testing to testing every day). The R* is inversely related to the implementation of NPI measures, such as masking and distancing. In the absence of any testing (purple curve), cumulative infections may be held below 5% of the campus population (horizontal red dashed line) if R* is <2.25 (that is, implementation of aggressive NPIs). With testing twice a week (yellow curve), that level of cumulative infections could be achieved at R* values of <4.2; with daily testing (blue curve), it could be achieved at R* values of <5.4. NPI = nonpharmaceutical intervention; R* = on-campus, effective reproduction number.

Figure 3.. Cumulative infections with 90% vaccine coverage and testing targeted to the unvaccinated population alone.

The figure reports the findings of the model under baseline input data assumptions, assuming 90% vaccination coverage. The curves denote the expected cumulative infections in the population over a 120-day semester (y-axis) under alternative frequencies of routine, asymptomatic testing of unvaccinated persons (ranging from daily testing to no asymptomatic testing). The R* is inversely related to the aggressiveness of NPI measures, such as masking and distancing. In the absence of any testing (purple curve), cumulative infections may be held below 5% of the campus population (horizontal red dashed line) if R* is kept <3.75. With testing twice a week (yellow curve), that level of cumulative infections could be achieved at R* values of <5.0; with daily testing (blue curve), it could be achieved at R* values of <5.6. NPI = nonpharmaceutical intervention; R* = on-campus, effective reproduction number.

Appendix Figure.. Sensitivity to vaccine effectiveness.

The figure reports cumulative infections under baseline input data assumptions but with vaccine preventive effectiveness lowered to 75% (decreasing to 50% at 6 months) and transmission effectiveness set to 0%. Asymptomatic testing is targeted to the unvaccinated population at frequencies ranging from no testing to daily testing. NPI = nonpharmaceutical intervention; R* = on-campus, effective reproduction number. A. With 50% vaccination coverage and in the absence of any testing (purple curve), the R* to hold cumulative infections below 5% (horizontal red dashed line) must now be <1.25 (from 1.5 under baseline conditions); with testing twice a week (yellow curve), the R* must remain below 2.4 (previously 3.5). The effects of lower vaccination effectiveness are more pronounced at higher vaccination coverage rates. B. At 70% coverage, in the absence of any testing (purple curve), the R* to hold cumulative infections below 5% (horizontal red dashed line) must now be <1.6 (from 2.25 under baseline conditions); with testing twice a week (yellow curve), the R* must remain below 2.3 (previously 4.5). C. At 90% coverage, in the absence of any testing (purple curve), the R* to hold cumulative infections below 5% (horizontal red dashed line) must now be <2.1 (from 3.75 under baseline conditions); with testing twice a week (yellow curve), the R* must remain below 2.4 (previously 5.0).