With increasing incidences of COVID-19 infections in the Greater Houston Area and students returning to school, informed decisions must be made regarding teacher and student continuous masking recommendations.
As of today (August 21),
To provide quantitative insight into these mixed stances, we ran a targeted simulation using our COVID-19 Outbreak Simulator to compare the number of COVID-cases that develop in schools that mandate or do not mandate mask wearing.
Disclaimer: This report was prepared by researchers in the Institute for Clinical & Translational Research, Baylor College of Medicine. It uses a limited model to predict the impact of mask wearing on COVID-19 incidences in public schools in the Greater Houston Area, and does not necessarily reflect the impact of other site specific COVID-prevention policies that may be in place at each of these schools.
The delta variant is highly infectious. With the Houston's existing high regional community infection rate we found that:
0.8%
of high school students will become infected at school. This risk is, however, lower than getting infected from the community (2.8%
). The proportions for school and community-based infections are higher for elementary schools(1.0%
and 3.0%
respectively) because students in elementary schools are not vaccinated.15.4%
of high school students will be infected within a month, and one fifth (21.0%
) all students in elementary schools will be infected. Again, we are assuming that there will be no post-infection contact tracing and testing will be performed so asymptomatic carriers will continue to attend school and infect others.1.8%
for high school students and 2.1%
for elementary school students if masks are worn. About 7.7%
of students in high school and 9.7%
of students in elementary schools will be isolated if masks are not worn.500
daily new cases in Harris County or 750
in the Greater Houston Area), students who will be isolated due to COVID-19 infections will be much lower, which will be around 0.5%
if masks are worn at all time, and 2.5%
if masks are not worn.90%
of all teachers are vaccinated and 60%
of high school students are vaccinated, there will still be a significant number of breakthrough cases.These results reflect our assumptions that
60%
of teachers are vaccinated, 30%
of high school students are vaccinated, and no students in elementary schools are vaccinated.20%
of all students and teachers have already been infected and recovered from COVID.Please see the Methods
section for details.
We ran 10,000
replicate simulations for each scenario and the following table lists
1600/million
now, but we also provide results for 400/million
for comparison purposes.90%
of teachers are vaccinated and 60%
of high school students are vaccinated.The complete results can be downloaded from our GitHub repository.
The following figure lists the perentage of students who might get infected at school, or isolated due to COVID symptoms (students may be infected both at school or from community, but my not show symptoms), under the assumptions that 60%
of teachers are vaccinated, 30%
of high school students are vaccinated, and no student from elementary school is vaccinated.
We assume that all students and teachers live in the same "community" that is subject to a fixed "community infection rate", which is the probability that people are infected. People who are infected from the community would go to school, with or without mask, and have the same probability of infecting others. People who show symptoms are isolated for 10 days before they go back to school, at which time they have recovered and are largely immune to reinfection. We do not yet model other post-infection reactions such as contact tracing and testing, which are being employed by many schools and universities to prevent the spread of the coronavirus.
We assume
Community infection rate (CIR): CIR is the actual community rate of infection and is used to model the probability at which people are infected. The actual number will differ from the Public Health reported confirmed case numbers due to reporting delays and the sufficiency of testing (see https://ourworldindata.org/covid-models for an expanded discussion). As of writing,
2000
confirmed cases per day in the Harris County with 4.7 M
people, or3000
confirmed cases per day in the Greater Houston Area with a population of about 9
million,so the raw CIR is about 400 / million
. Using a popular method to adjust for the under-reporting of actual CIR, namely multiplying the number of confirmed cases by a factor of 4, we use 1600 / million as the CIR for the Greater Houston Area. Note that the estimates from The Institute for Health Metrics and Evaluation (IHME) an independent global health research center at the University of Washington is around 2121 per million for the state of Texas.
Vaccination coverage: According to government report, 45.7% of people are fully vaccinated in Texas. We assume that adults (teachers) have higher vaccination rates and assume that
60%
of teachers and staff are vaccinated in both high schools and elementary schools.30%
of students are vaccinated in high schools.90%
of teachers are vaccinated and 60%
of high school students are vaccinated.Size of schools: According to online information, we assume that
Transmissibility of virus: The highly contagious delta variant has become the most prevalent version of COVID-19 in the country, and also in the state of Texas. The delta variant has
6.5
for symptomatic cases (range 5-8)4.6
for asymptomatic carriers because we assume that asymptomatic carriers are 70% infectious compared to symptomatic carriers.4.4
30%
of people will remain asymptomatic after being infected.20%
of the population (teachers and students) have already been infected, and recovered. They are less susceptible to another infection (50%
reduction) and have lower viral load (50%
reduction) if they are infected. Infection patterns:
25
classes with 20
students each. Because students in elementary schools usually only interact with their classmates and teachers, we assume that each student will interact with the rest of the class (19
students), 3
teachers, and 5
random students they interact at hall way or cafeterias.Post-infection reaction:
Efficacy of vaccine: Most Houstonians were vaccinated with the Pfizer vaccine, which is reported to
42%
efficacy for preventing infection50%
50%
efficacy for preventing secondary infection.Duration of simulation: We simulate the operation of schools for a month (28 days, 20 working days).
Mask wearing: We simulate three scenarios,
We output the number of infections and symptomatic cases in both high schools and elementary schools.