Evaluation of test-to-return after COVID-19 diagnosis in a Massachusetts public school district (preprint)

The Centers for Disease Control allows rapid antigen testing (RAT) towards the end of a 5-day isolation for COVID-19 infection to determine eligibility to leave isolation. The impact of a test-to-return (TTR) program in schools is unknown. In January 2022 a Massachusetts school district initiated a TTR program utilizing a single school-administered RAT on days 5-9 after symptom onset or positive test, whichever was first. Of 636 students with COVID-19 infection, 408 (64.2%) participated in TTR; of these, 128 (31.4%) had a positive TTR rapid antigen test. Students who were symptomatic at any time during their infection were more likely to have a positive TTR than those who were never symptomatic (43.1% vs. 17.3%); positivity rates were lower when TTR was performed later during days 6-9. TTR may identify students who carry higher viral loads after recovery from COVID-19 infection thereby extending their isolation, while facilitating earlier return of those with negative results.

Resources Required for Implementation of SARS-CoV-2 Screening in Massachusetts K-12 Public Schools in Winter/Spring 2021 (preprint)

Importance CDC guidance emphasizes the importance of in-person education for students in grades kindergarten to 12 (K-12) during the COVID-19 pandemic. CDC encourages weekly SARS-CoV-2 testing of asymptomatic, unvaccinated students and staff ("screening") to reduce infection risk and provide data about in-school SARS-CoV-2 prevalence where community incidence is high. The financial costs of screening assays have been described, but the human resource requirements at the school and district level to implement a SARS-CoV-2 screening program are not well known. Objective To quantify the resources required to implement a screening program in K-12 schools. Design, Setting, and Participants A consortium of Massachusetts public K-12 schools was formed to implement and evaluate a range of SARS-CoV-2 screening approaches. Participating districts were surveyed weekly about their programs, including: type of assay used, individual vs. pooled screening, approaches to return of results and deconvolution (identification of positive individual specimens) of positive pools, number and type of personnel implementing the screening program, and hours spent on program implementation. Main Outcomes and Measures Costs, resource utilization Results In 21 participating districts, over 21 weeks from January to June 2021, the positivity rate was 0.0%-0.21% among students and 0.0%-0.13% among educators/staff, and 4 out of 21 (19%) districts had at least one classroom transition to remote learning at any point due to a positive case. The average weekly cost to implement a screening program, including assay and personnel costs, was $17.00 per person tested; this was $46.68 for individual screenings and $15.61 for pooled screenings. The total weekly costs by district ranged from $1,644-$93,486, and districts screened between 58 and 3,675 people per week. The reported number of personnel working per week ranged from 1-5 to >50, and the total number of hours worked by all personnel ranged from 5-10 to >50. Conclusion and Relevance The human resources required to implement SARS-CoV-2 screening in Massachusetts public K-12 schools were substantial. Where screening is recommended for the 2021-22 school year due to high COVID-19 incidence (e.g., where vaccination uptake is low and/or more infectious variants predominate), understanding the human resources required to implement screening will assist districts policymakers in planning.

Prevalence and risk factors for in-school transmission of SARS-CoV-2 in Massachusetts K-12 public schools, 2020-2021 (preprint)

IntroductionThe SARS-CoV-2 secondary attack rate (SAR) in schools is low when mitigation measures are adopted, Data on the relative impact of such strategies are limited. We evaluated the SARS-CoV-2 SAR in Massachusetts schools during 2020-21 and factors associated with transmission risk. MethodsIn a convenience sample of 25 Massachusetts public K-12 school districts, de-identified information about SARS-CoV-2 cases and their school-based contacts was reported using a standardized contact-tracing tool. Index cases were included if they were in school while infectious. SAR was defined as the proportion of in-school contacts acquiring SARS-CoV-2 infection and designated as possible or probable in-school transmission by school-based teams. We compared exposure-specific SAR using unadjusted risk ratios (RR) with 95% confidence intervals (CI); p-values were calculated using Fishers exact tests. ResultsEight districts (70 schools with >33,000 enrolled students) participated. There were 435 index cases and 1,771 school-based contacts (Table 1). Most contacts (1327/1771 [75%]) underwent SARS-CoV-2 testing and 39/1327 (2.9%) contacts tested positive. Of 39 positive contacts, 10 (25.6%) had clear out-of-school exposures and were deemed not in-school transmissions, so were excluded from further calculations. Twenty-nine (74.4%) contacts were deemed possible or probable in-school transmissions, resulting in an in-school SAR of 2.2%. Of the 29 in-school transmissions, 6 (20.7%) were staff-to-staff, 7 (24.1%) were staff-to-student, 3 (10.3%) were student-to-staff, and 13 (44.8%) were student-to-student; 6 (20.7%) occurred from index cases attending work/school while symptomatic. The unadjusted SAR (Table 2) was significantly higher if the index case was a staff member versus a student (RR 2.18, 95% CI 1.06-4.49; p=0.030), if the index case was identified via in-school contact tracing versus via school-based asymptomatic testing (RR 8.44, 95% CI 1.98-36.06; p=0.001), if the exposure occurred at lunch versus elsewhere (RR 5.74, 95% CI 2.11-15.63; p<0.001; all lunch transmissions were staff-to-staff), and if both parties were unmasked versus both masked (RR 6.98, 95% CI 3.09-15.77; p<0.001). For students, SAR did not differ by grade level. O_TBL View this table: org.highwire.dtl.DTLVardef@1b1f706org.highwire.dtl.DTLVardef@d0cea9org.highwire.dtl.DTLVardef@afcd27org.highwire.dtl.DTLVardef@1c5e7e7org.highwire.dtl.DTLVardef@1fc0731_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 1:C_FLOATNO O_TABLECAPTIONNumber of SARS-CoV-2 index cases, possible and probable in-school transmissions, secondary attack rates, and number of contacts per index case in 8 Massachusetts K-12 public school districts, 2020-21 C_TABLECAPTION C_TBL O_TBL View this table: org.highwire.dtl.DTLVardef@13c5853org.highwire.dtl.DTLVardef@cac231org.highwire.dtl.DTLVardef@1931f5eorg.highwire.dtl.DTLVardef@1f095c1org.highwire.dtl.DTLVardef@1f7bc21_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 2:C_FLOATNO O_TABLECAPTIONNumber of index cases and contacts and secondary attack rate by type of exposure: 8 public MA K-12 districts, 2020-21 C_TABLECAPTION C_TBL ConclusionsSecondary attack rates for SARS-CoV-2 were low in public school settings with comprehensive mitigation measures in place before the emergence of the delta variant; lack of masking and staff-to-staff dining were associated with increased risk.

When do elementary students need masks in school? Model-estimated risk of in-school SARS-CoV-2 transmission and related infections among household members before and after student vaccination (preprint)

BackgroundWhile CDC guidance for K-12 schools recommends indoor masking regardless of vaccination status, final decisions about masking in schools will be made at the local and state level. The impact of the removal of mask restrictions, however, on COVID-19 outcomes for elementary students, educators/staff, and their households is not well known. MethodsWe used a previously published agent-based dynamic transmission model of SARS-CoV-2 in K-12 schools to simulate an elementary school with 638 students across 6 scenarios: combinations of three viral infectiousness levels (reflecting wild-type virus, alpha variant, and delta variant) and two student vaccination levels (0% and 50% coverage to reflect potential authorization in this age group). For each scenario, we varied observed community COVID-19 incidence (0 to 50 cases/100,000 people/day) and mitigation effectiveness (0-100% reduction to in-school secondary attack rate), and evaluated two outcomes over a 30 day period: (1) the probability of at least one in-school transmission, and (2) the increase in total cases among students, educators/staff, and their household members between in-person and remote instruction. ResultsOver 30 days in the simulated elementary school, the probability of at least one in-school SARS-CoV-2 transmission and the number of projected infections in the immediate school community varied widely. In one scenario with the delta variant and no student vaccination, assuming that baseline mitigation measures of simple ventilation and handwashing reduce the secondary attack rate by 40%, if decision-makers seek to keep the monthly probability of an in-school transmission below 50%, additional mitigation (e.g., masking) would need to be added at a community incidence of approximately 4/100,000/day. Once students are vaccinated, thresholds shift substantially higher. LimitationsThe interpretation of model results should be limited by the uncertainty in many of the parameters, including the effectiveness of individual mitigation interventions and vaccine efficacy against the delta variant, and the limited scope of the model beyond the school community. Additionally, the assumed case detection rate (33% of cases detected) may be too high in areas with decreased testing capacity. ConclusionDespite the assumption of high adult vaccination, the risks of both in-school SARS-CoV-2 transmission and resulting infections among students, educators/staff, and their household members remain high when the delta variant predominates and students are unvaccinated. Mitigation measures or vaccinations for students when available can substantially reduce these risks. These findings underscore the potential role for responsive plans, where mitigation is deployed based on local COVID-19 incidence and vaccine uptake.

Weekly SARS-CoV-2 screening of asymptomatic students and staff to guide and evaluate strategies for safer in-person learning (preprint)

Background: Data suggest that COVID-19 transmission in K-12 schools is uncommon, but few studies have confirmed this using widespread screening of asymptomatic individuals. Objective: To evaluate the incidence of asymptomatic COVID-19, document the frequency of in-school transmission, and confirm feasibility of widespread asymptomatic screening in schools. Design: Prospective observational study Setting: Single mid-sized suburban school district including 10 schools and a central office. Participants: District staff and students Interventions: Asymptomatic screening PCR for SARS-CoV-2 Measurements: Concurrent with a hybrid model and layered mitigation, weekly pooled testing of staff and secondary students was offered using saliva samples collected at home. Identification of >1 case in a school prompted investigation for possible in-school transmission. Staff and families were surveyed about satisfaction with the screening program. Results: From weeks 1-18, rates of incident COVID-19 in the surrounding community rose steadily. Weekly staff and student screening identified 0-7 asymptomatic cases/week. In week 7, 5 cases were identified among staff who shared an office setting. Enhancements to mitigation strategies were undertaken. The proportion of survey respondents self-reporting comfort with in-person learning before versus after implementation of screening increased. Limitations: Because screening testing was not mandatory, the results from the participating population might not represent the entire school community. Conclusions: In this school district with layered mitigation measures, in-school transmission was rare. The program identified a cluster with in-school staff-to-staff transmission and spurred enhancement of safety strategies. A weekly COVID-19 screening program can provide critical data to inform mitigation efforts, and provides school-specific, current data to inform decisions about in-person learning models. Screening provided reassurance and identified asymptomatic cases. Funding: The Wellesley Education Foundation provided funding for the testing.

College campuses and COVID-19 mitigation: clinical and economic value (preprint)

BackgroundDecisions around US college and university operations will affect millions of students and faculty amidst the COVID-19 pandemic. We examined the clinical and economic value of different COVID-19 mitigation strategies on college campuses. MethodsWe used the Clinical and Economic Analysis of COVID-19 interventions (CEACOV) model, a dynamic microsimulation that tracks infections accrued by students and faculty, accounting for community transmissions. Outcomes include infections, $/infection-prevented, and $/quality-adjusted-life-year ($/QALY). Strategies included extensive social distancing (ESD), masks, and routine laboratory tests (RLT). We report results per 5,000 students (1,000 faculty) over one semester (105 days). ResultsMitigation strategies reduced COVID-19 cases among students (faculty) from 3,746 (164) with no mitigation to 493 (28) with ESD and masks, and further to 151 (25) adding RLTq3 among asymptomatic students and faculty. ESD with masks cost $168/infection-prevented ($49,200/QALY) compared to masks alone. Adding RLTq3 ($10/test) cost $8,300/infection-prevented ($2,804,600/QALY). If tests cost $1, RLTq3 led to a favorable cost of $275/infection-prevented ($52,200/QALY). No strategies without masks were cost-effective. ConclusionExtensive social distancing with mandatory mask-wearing could prevent 87% of COVID-19 cases on college campuses and be very cost-effective. Routine laboratory testing would prevent 96% of infections and require low cost tests to be economically attractive.

Clinical Impact, Costs, and Cost-Effectiveness of Expanded SARS-CoV-2 Testing in Massachusetts (preprint)

BackgroundWe projected the clinical and economic impact of alternative testing strategies on COVID-19 incidence and mortality in Massachusetts using a microsimulation model. MethodsWe compared five testing strategies: 1) PCR-severe-only: PCR testing only patients with severe/critical symptoms; 2) Self-screen: PCR-severe-only plus self-assessment of COVID-19-consistent symptoms with self-isolation if positive; 3) PCR-any-symptom: PCR for any COVID-19-consistent symptoms with self-isolation if positive; 4) PCR-all: PCR-any-symptom and one-time PCR for the entire population; and, 5) PCR-all-repeat: PCR-all with monthly re-testing. We examined effective reproduction numbers (Re, 0.9-2.0) at which policy conclusions would change. We used published data on disease progression and mortality, transmission, PCR sensitivity/specificity (70/100%) and costs. Model-projected outcomes included infections, deaths, tests performed, hospital-days, and costs over 180-days, as well as incremental cost-effectiveness ratios (ICERs, $/quality-adjusted life-year [QALY]). ResultsIn all scenarios, PCR-all-repeat would lead to the best clinical outcomes and PCR-severe-only would lead to the worst; at Re 0.9, PCR-all-repeat vs. PCR-severe-only resulted in a 63% reduction in infections and a 44% reduction in deaths, but required >65-fold more tests/day with 4-fold higher costs. PCR-all-repeat had an ICER

Cost-effectiveness of public health strategies for COVID-19 epidemic control in South Africa (preprint)

Background Healthcare resource constraints in low and middle-income countries necessitate selection of cost-effective public health interventions to address COVID-19. Methods We developed a dynamic COVID-19 microsimulation model to evaluate clinical and economic outcomes and cost-effectiveness of epidemic control strategies in KwaZulu-Natal, South Africa. Interventions assessed were Healthcare Testing (HT), where diagnostic testing is performed only for those presenting to healthcare centres; Contact Tracing (CT) in households of cases; Isolation Centres (IC), for cases not requiring hospitalisation; community health worker-led Mass Symptom Screening and diagnostic testing for symptomatic individuals (MS); and Quarantine Centres (QC), for contacts who test negative. Given uncertainties about epidemic dynamics in South Africa, we evaluated two main epidemic scenarios over 360 days, with effective reproduction numbers (Re) of 1.5 and 1.2. We compared HT, HT+CT, HT+CT+IC, HT+CT+IC+MS, HT+CT+IC+QC, and HT+CT+IC+MS+QC, considering strategies with incremental cost-effectiveness ratio (ICER)