Model-based assessment of SARS-CoV-2 Delta variant transmission dynamics within partially vaccinated K-12 school populations (preprint)

BackgroundWe examined school reopening policies amidst rising transmission of the highly transmissible Delta variant, accounting for vaccination among individuals aged 12 years and older, with the goal of characterizing risk to students and teachers under various within-school non-pharmaceutical interventions (NPIs) combined with specific vaccination coverage levels. MethodsWe developed an individual-based transmission model to simulate transmission of the Delta variant of SARS-CoV-2 among a synthetic population, representative of Bay Area cities. We parameterized the model using community contact rates from vaccinated households ascertained from a household survey of Bay Area families with children conducted between February - April, 2021. Interventions and outcomesWe evaluated the additional infections in students and teachers/staff resulting over a 128-day semester from in-school instruction compared to remote instruction when various NPIs (mask use, cohorts, and weekly testing of students/teachers) were implemented in schools, across various community-wide vaccination coverages (50%, 60%, 70%), and student ([≥]12 years) and teacher/staff vaccination coverages (50% - 95%). We quantified the added benefit of universal masking over masking among unvaccinated students and teachers, across varying levels of vaccine effectiveness (45%, 65%, 85%), and compared results between Delta and Alpha variant circulation. ResultsThe Delta variant sharply increases the risk of within-school COVID-transmission when compared to the Alpha variant. In our highest risk scenario (50% community and within-school vaccine coverage, no within-school NPIs, and predominant circulation of the Delta variant), we estimated that an elementary school could see 33-65 additional symptomatic cases of COVID-19 over a four-month semester (depending on the relative susceptibility of children <10 years). In contrast, under the Bay Area reopening plan (universal mask use, community and school vaccination coverage of 70%), we estimated excess symptomatic infection attributable to school reopening among 2.0-9.7% of elementary students (8-36 excess symptomatic cases per school over the semester), 3.0% of middle school students (13 cases per school) and 0.4% of high school students (3 cases per school). Excess rates among teachers attributable to reopening were similar. Achievement of lower risk tolerances, such as <5 excess infections per 1,000 students or teachers, required a cohort approach in elementary and middle school populations. In the absence of NPIs, increasing the vaccination coverage of community members from 50% to 70% or elementary teachers from 70% to 95% reduced the estimated excess rate of infection among elementary school students attributable to school transmission by 24% and 41%, respectively. We estimated that with 70% coverage of the eligible community and school population with a vaccine that is [≤]65% effective, universal masking can avert more cases than masking of unvaccinated persons alone. ConclusionsAmidst circulation of the Delta variant, our findings demonstrated that schools are not inherently low risk, yet can be made so with high community vaccination coverages and universal masking. Vaccination of adult community members and teachers protects unvaccinated elementary and middle school children. Elementary and middle schools that can support additional interventions, such as cohorts and testing, should consider doing so, particularly if additional studies find that younger children are equally as susceptible as adults to the Delta variant of SARS-CoV-2. LimitationsWe did not consider the effect of social distancing in classrooms, or variation in testing frequency, and considerable uncertainty remains in key transmission parameters.

Changes in household food security, access to health services, and income in northern Lao PDR during the COVID-19 pandemic (preprint)

BackgroundThe COVID-19 pandemic is expected to exacerbate food insecurity in low- and middle-income countries, through loss of income and disrupted food supply chains. Lao PDR has among the highest rates of malnutrition in Southeast Asia. We assessed the relative difficulty in meeting food needs during the COVID-19 pandemic in rural districts of Luang Prabang Province, Lao PDR compared to before; determined associations between pandemic-associated difficulties in food access and household, maternal and child food security; and identified resiliency-promoting strategies. MethodsIn November 2020, households (N = 1,122) with children under five years were interviewed. Respondents reported the relative ease of access of food and health care as well as changes in income and expenditures compared to before March 2020. We used generalized linear models with cluster robust standard errors to assess univariate and multivariate associations. ResultsNearly four-fifths (78.5%) found it harder to meet household food needs during the pandemic. The most common reasons were increased food prices (51.2%), loss of income (45.3%), and decreased food availability (36.6%). Adjusting for demographics, households with increased difficulty meeting food needs had lower food consumption scores and child dietary diversity. Over 85% of households lost income during the pandemic. Decreased expenditures was associated with reliance on more extreme coping strategies to meet food needs. The households who experienced no change in meeting food needs produced a greater percentage of their food from homegrown methods (4.22% more, 95% CI: 1.28, 7.15), than households who found it more difficult. We estimated that decreases in child bodyweight by 0.5 - 1% would increase wasting in this population by 1.7 - 2.1 percentage points. ConclusionsPandemic-associated shocks may have large effects on malnutrition prevalence. Action is needed to mitigate consequences of the pandemic on nutrition. Local food production and safety net programs that offset income losses may help. Summary BoxO_ST_ABSWhat is already known?C_ST_ABSThe COVID-19 pandemic has disrupted food supply chains and livelihoods, causing concerns that a global nutrition crisis is imminent and prompting leaders from United Nations agencies to issue an immediate call to action to direct funds towards prevention of child malnutrition. While documented COVID-19 transmission in Lao PDR was lower than that of surrounding counties, malnutrition rates are high, particularly in the northern province of Luang Prabang, which is heavily reliant on tourism for livelihoods. What are the new findings?Nearly four-fifths of those interviewed in Luang Prabang Province, Lao PDR reported that it was harder to meet their households food needs, compared to before the pandemic, with 51% attributing the reason to increased food prices. Over 85% of households reported losing income. Lower expenditures and increased difficulty obtaining food were both associated with lower household food consumption scores and higher household coping strategies, in adjusted analyses. Households who obtained a greater proportion of their foods through home production appeared more resilient than households who obtained a greater proportion of their foods through purchasing. What do the new findings imply?The pandemic may deeply exacerbate food insecurity in Lao PDR, potentially leading to increases in child wasting. Increased local food production and establishment of safety net programs that offset income losses may be two strategies that address this problem among this population.

The effect of school closures and reopening strategies on COVID-19 infection dynamics in the San Francisco Bay Area: a cross-sectional survey and modeling analysis (preprint)

Background Large-scale school closures have been implemented worldwide to curb the spread of COVID-19. However, the impact of school closures and re-opening on epidemic dynamics remains unclear. Methods We simulated COVID-19 transmission dynamics using an individual-based stochastic model, incorporating social-contact data of school-aged children during shelter-in-place orders derived from Bay Area (California) household surveys. We simulated transmission under observed conditions and counterfactual intervention scenarios between March 17-June 1, and evaluated various fall 2020 K-12 reopening strategies. Findings Between March 17-June 1, assuming children <10 were half as susceptible to infection as older children and adults, we estimated school closures averted a similar number of infections (13,842 cases; 95% CI: 6,290, 23,040) as workplace closures (15,813; 95% CI: 9,963, 22,617) and social distancing measures (7,030; 95% CI: 3,118, 11,676). School closure effects were driven by high school and middle school closures. Under assumptions of moderate community transmission, we estimate that fall 2020 school reopenings will increase symptomatic illness among high school teachers (an additional 40.7% expected to experience symptomatic infection, 95% CI: 1.9, 61.1), middle school teachers (37.2%, 95% CI: 4.6, 58.1), and elementary school teachers (4.1%, 95% CI: -1.7, 12.0). Results are highly dependent on uncertain parameters, notably the relative susceptibility and infectiousness of children, and extent of community transmission amid re-opening. The school-based interventions needed to reduce the risk to fewer than an additional 1% of teachers infected varies by grade level. A hybrid-learning approach with halved class sizes of 10 students may be needed in high schools, while maintaining small cohorts of 20 students may be needed for elementary schools. Interpretation Multiple in-school intervention strategies and community transmission reductions, beyond the extent achieved to date, will be necessary to avoid undue excess risk associated with school reopening. Policymakers must urgently enact policies that curb community transmission and implement within-school control measures to simultaneously address the tandem health crises posed by COVID-19 and adverse child health and development consequences of long-term school closures.