No magic bullet: Limiting in-school transmission in the face of variable SARS-CoV-2 viral loads

Abstract

In the face of a long-running pandemic, understanding the drivers of ongoing SARS-CoV-2 transmission is crucial for the rational management of COVID-19 disease burden. Keeping schools open has emerged as a vital societal imperative during the pandemic, but in-school transmission of SARS-CoV-2 can contribute to further prolonging the pandemic. In this context, the role of schools in driving SARS-CoV-2 transmission acquires critical importance. Here we model in-school transmission from first principles to investigate the effectiveness of layered mitigation strategies on limiting in-school spread. We examined the effect of masks and air quality (ventilation, filtration and ionizers) on steady-state viral load in classrooms, as well as on the number of particles inhaled by an uninfected person. The effectiveness of these measures in limiting viral transmission was assessed for variants with different levels of mean viral load (ancestral, Delta, Omicron). Our results suggest that a layered mitigation strategy can be used effectively to limit in-school transmission, with certain limitations. First, poorly designed strategies (insufficient ventilation, no masks, staying open under high levels of community transmission) will permit in-school spread even if some level of mitigation is present. Second, for viral variants that are sufficiently contagious, it may be difficult to construct any set of interventions capable of blocking transmission once an infected individual is present, underscoring the importance of other measures. Our findings provide practical recommendations; in particular, the use of a layered mitigation strategy that is designed to limit transmission, with other measures such as frequent surveillance testing and smaller class sizes (such as by offering remote schooling options to those who prefer it) as needed.

Vaccines Alone Cannot Slow the Evolution of SARS-CoV-2

“…NPIs complement vaccines in slowing viral evolution by limiting the transmission of novel vaccine-evading mutants (Figure 3). In the real world, vaccinal efficacy is degraded by two phenomena: the pharmacokinetic decay of neutralizing antibody titers and the rate of evolution of immune evasion by the virus (see [42] and Supplemental Text Section S8 in [43] for more details). We examined the hypothetical case of a vaccine whose efficacy was not degraded by immune-evading variants to identify the rate of vaccination required to prevent the generation of novel variants (Figure 4).…”

On a model-based approach to improve intranasal spray targeting for respiratory viral infections

“…An early intervention method that can target the initial dominant infection site (i.e., the nasopharynx) is imperative for limiting asymptomatic transmission (Van Egeren et al, 2022) of the exhaled pathogenic particulates as well as for preventing systemic lower airway progression of the disease in a host, aggravating toward severe illness (He et al, 2020;Sungnak et al, 2020). Of critical interest here: based on the brisk pace at which lower airway infections often ensue after the emergence of initial symptoms, it has been conjectured that the nasopharynx also acts as the seeding zone for the spread of a respiratory viral disease to the lungs via lower airway aspiration of virus-laden boluses of nasopharyngeal fluids (Hou et al, 2020;Basu et al, 2022a;Chen et al, 2022).…”