Estimating the nationwide transmission risk of measles in US schools and impacts of vaccination and supplemental infection control strategies

Abstract

Background: The spread of airborne infectious diseases such as measles is a critical public health concern. The U.S. was certified measles-free in 2000, but the number of measles cases has increased in recent years breaking the record of the nationwide annual number of cases since 1992. Although the characteristics of schools have made them one of the most vulnerable environments during infection outbreaks, the transmission risk of measles among students is not completely understood. We aimed to evaluate how three factors influence measles transmission in schools: personal (vaccination), social (compartmentalizing), and building systems (ventilation, purification, and filtration). Methods: We used a combination of a newly developed multi-zone transient Wells-Riley approach, a nationwide representative School Building Archetype (SBA) model, and a Monte-Carlo simulation to estimate measles risk among U.S. students. We compared our risk results with the range of reported transmission rates of measles in school outbreaks to validate the risk model. We also investigated the effectiveness of vaccination and ten supplemental infection control scenarios for reducing the risk of measles transmission among students. Results: Our best nationwide estimate of measles transmission risk in U.S. schools were 3.5 and 32% among all (both unvaccinated and immunized) and unvaccinated students, respectively. The results showed the transmission risk of measles among unvaccinated students is > 70 times higher than properly immunized ones. We also demonstrated that the transmission risk of measles in primary schools (assuming teacher self-contained classrooms) is less than secondary schools (assuming departmentalized systems). For building-level interventions, schools with ductless-with-air-filter and ductless-without-air-filter systems have the lowest and highest transmission risks of measles, respectively. Finally, our simulation showed that infection control strategies could cut the average number of infected cases among all students in half when a combination of advanced air filtration, ventilation, and purification was adopted in the modeled schools. Conclusions: Our results highlight the primary importance of vaccination for reducing the risk of measles transmission among students. Yet, additional and significant risk reduction can be achieved through compartmentalizing students and enhancing building ventilation and filtration systems.

The airborne contagiousness of respiratory viruses: A comparative analysis and implications for mitigation

“… 65 th 35 th 600 (median) 84 th 59 th 5600 (max.) 95 th 80 th Measles: Secondary school Azimi et al (2020) 2765 92 nd 74 th Measles: Pediatrician’s office Remington et al (1985) 8640 96 th 83 rd Influenza: Human transmission trials in quarantine rooms Bueno de Mesquita et al (2020) 0.11 41 st 4 th Influenza: Transmission experiments among ferrets Zhou et al (2018) 7.95 98 th 69 th Influenza: Airliner during delay with inoperable ventilation Moser et al, 1979 , Rudnick and Milton, 2003 79 -- 95 th Rhinovirus: Transmission trials using card playing games Dick et al (1987) ; Rudnick and Milton (2003) 3.1 72 nd 18 th …”

“…The pattern of the spread of measles in schools studied by Wells in the pre-vaccine era was consistent with past epidemiology showing outbreaks to begin when the density of susceptibles reached 30%–40%, and wane when the density decreased to 15%–20% ( Wells, 1943 , Wells, 1955 ). Conversely, the post-vaccine era estimates are based on superspreading events with back calculated emission rates reaching over 1000 quanta h –1 ( Riley, 1980 , Remington et al, 1985 , Azimi et al, 2020 ). This discrepancy is potentially explained by the impact of the density of susceptibles on the threshold emission rate needed to reproduce infection.…”

The impact of heating, ventilation, and air conditioning design features on the transmission of viruses, including the 2019 novel coronavirus: a systematic review of filtration

“…Nine of the filtration studies were modelling, employing the following models: one-dimensional analytical model, 41 Wells-Riley model, [42][43][44][45] CONTAM multi-zone IAQ model, 46 Susceptible-Exposed-Infectious-Recovered (SEIR) model, 43 an indoor contact model, 43 a control volume conservation model, 47 Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, 48 School Building Archetype (SBA) model using both the Wells-Riley and Monte-Carlo approaches, 44 the multi-region FATE model of Fauske & Associates, 45 and doseresponse model. 49 Viruses investigated include SARS-CoV-2, 45,49 measles with influenza size distributions, 44 influenza, [42][43]46 rhinovirus, 46 PRRSV, 47 avian influenza, 48 and virus modelled as gas. 41 Augenbraun et al 49 sought to examine SARS-CoV-2 but the relevant infectivity parameters were set to that of influenza.…”

“…No restrictions Publication status Published, peer-reviewed Unpublished, not peerreviewed CFD = computational fluid dynamics; HVAC = heating, ventilation, and air conditioning; MERV = minimum efficiency reporting value; UVGI = ultraviolet germicidal irradiation 41 low low low Azimi (2013) 42 low low low Brown (2014) 46 low low low Zheng (2016) 43 low low low Janni (2018) 47 low low low Zhao (2019) 48 low low low Augenbraun (2020) unclear low low Azimi (2020) 44 low low low Kennedy (2020) 45 unclear low low Figure 1. Flow of studies through the selection process (note: search was conducted for all HVAC design features but only studies of filtration are included in this manuscript)…”

Modeling and Controlling Epidemic Outbreaks: The Role of Population Size, Model Heterogeneity and Fast Response in the Case of Measles

“…We simulated several scenarios to conduct a sensitivity analysis for the less stylized case of transmission between two schools, a smaller elementary school of 500 students and a high school with 2000 students. We assumed that initially there was a single infected case in the elementary school as measles cases were more likely to appear in the elementary school [62].…”