Abstract:Background
Routine testing for SARS-CoV-2 in the community is essential for guiding key epidemiological decisions from the quarantine of individual patients to enrolling regional and national preventive measures. Yet, the primary testing tool, the RT-qPCR based testing, is notoriously known for its low sensitivity, i.e. high risk of missed detection of carriers. Quantifying the false-negative rate (FNR) of the RT-qPCR test at the community settings and its dependence on patient demographic and disease progress… Show more
“…We assume 75% sensitivity for individuals in the first 2 days of their pre-symptomatic period and 80% sensitivity for any pre-symptomatic days beyond that. Sensitivities for symptomatic and asymptomatic individuals alike follow the time course shown in Figure A2, which follows from Levine-Tiefenbrun et al (69). We assume there are no false positives. Figure A2: Test sensitivities. The probability of returning a positive test results when testing an individual in a symptomatic ( I sym or asymptomatic I asym infectious state as a function of the number of days since entering that state (i.e., days since onset of symptoms).…”
“…We assume 75% sensitivity for individuals in the first 2 days of their pre-symptomatic period and 80% sensitivity for any pre-symptomatic days beyond that. Sensitivities for symptomatic and asymptomatic individuals alike follow the time course shown in Figure A2, which follows from Levine-Tiefenbrun et al (69). We assume there are no false positives.…”
Reopening schools is an urgent priority as the COVID-19 pandemic drags on. To explore the risks associated with returning to in-person learning and the value of mitigation measures, we developed stochastic, network-based models of SARS-CoV-2 transmission in primary and secondary schools. We find that a number of mitigation measures, alone or in concert, may reduce risk to acceptable levels particularly when community prevalence is low. Student cohorting, in which students are divided into two separate populations that attend in-person classes on alternating schedules, can reduce both the likelihood and the size of outbreaks. Proactive testing of teachers and staff once or twice a week can help catch introductions early, before they spread widely through the school. In secondary schools, where the students are more susceptible to infection and have different patterns of social interaction, control is more difficult. Especially in these settings, planners should also consider testing students once or twice weekly. Vaccinating teachers and staff protects these individuals and---when vaccines block SARS-CoV-2 transmission in addition to symptoms---may also have a protective effect on students as well. Other mitigations, including mask-wearing, social distancing, and increased ventilation, remain a crucial component of any reopening plan.
“…We assume 75% sensitivity for individuals in the first 2 days of their pre-symptomatic period and 80% sensitivity for any pre-symptomatic days beyond that. Sensitivities for symptomatic and asymptomatic individuals alike follow the time course shown in Figure A2, which follows from Levine-Tiefenbrun et al (69). We assume there are no false positives. Figure A2: Test sensitivities. The probability of returning a positive test results when testing an individual in a symptomatic ( I sym or asymptomatic I asym infectious state as a function of the number of days since entering that state (i.e., days since onset of symptoms).…”
“…We assume 75% sensitivity for individuals in the first 2 days of their pre-symptomatic period and 80% sensitivity for any pre-symptomatic days beyond that. Sensitivities for symptomatic and asymptomatic individuals alike follow the time course shown in Figure A2, which follows from Levine-Tiefenbrun et al (69). We assume there are no false positives.…”
Reopening schools is an urgent priority as the COVID-19 pandemic drags on. To explore the risks associated with returning to in-person learning and the value of mitigation measures, we developed stochastic, network-based models of SARS-CoV-2 transmission in primary and secondary schools. We find that a number of mitigation measures, alone or in concert, may reduce risk to acceptable levels particularly when community prevalence is low. Student cohorting, in which students are divided into two separate populations that attend in-person classes on alternating schedules, can reduce both the likelihood and the size of outbreaks. Proactive testing of teachers and staff once or twice a week can help catch introductions early, before they spread widely through the school. In secondary schools, where the students are more susceptible to infection and have different patterns of social interaction, control is more difficult. Especially in these settings, planners should also consider testing students once or twice weekly. Vaccinating teachers and staff protects these individuals and---when vaccines block SARS-CoV-2 transmission in addition to symptoms---may also have a protective effect on students as well. Other mitigations, including mask-wearing, social distancing, and increased ventilation, remain a crucial component of any reopening plan.
“…Similar preliminary results are emerging for the Pfizer vaccine 32, 41 and for AstraZeneca vaccine 6 . As well, substantial reduction in viral loads have been found among those who are infected for both the AstraZeneca vaccine 25 and the BioNTech/Pfizer BNT162b2 vaccine 37, 44 , suggesting reduced further transmission even when infection does occur. Given these data, the impact of vaccination on transmission is likely to be strong, and jurisdictions which have planned predominantly oldest-first vaccination rollouts may now wish to use vaccination to reduce transmission more rapidly.…”
In planning for upcoming mass vaccinations against COVID-19, many jurisdictions have proposed using primarily age-based rollout strategies, where the oldest are vaccinated first and the youngest last. In the wake of growing evidence that approved vaccines are effective at preventing not only adverse outcomes, but also infection (and hence transmission of SARS-CoV-2), we propose that such age-based rollouts are both less equitable and less effective than strategies that prioritize essential workers. We demonstrate using modelling that strategies that target essential workers earlier consistently outperform those that do not, and that prioritizing essential workers provides a significant level of indirect protection for older adults. This conclusion holds across numerous outcomes, including cases, hospitalizations, deaths, prevalence of Long COVID, chronic impacts of COVID, quality adjusted life years lost and net monetary benefit lost. It also holds over a range of possible values for the efficacy of vaccination against infection. Our analysis focuses on regimes where the pandemic continues to be controlled with distancing and other measures as vaccination proceeds, and where the vaccination strategy is expected to last for over the coming 6-8 months - for example British Columbia, Canada. In such a setting with a total population of 5M, vaccinating essential workers sooner is expected to prevent over 200,000 infections, over 600 deaths, and to produce a net monetary benefit of over $500M. 20-25% of the quality adjusted life years lost, and 28-34% of the net monetary benefit lost, are due to chronic impacts of COVID-19.
“…We next compared the Ct values of these post-vaccination infections with Ct values of positive tests of unvaccinated patients. As viral loads could be associated with age and sex 9 is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)…”
mentioning
confidence: 99%
“…We next compared the Ct values of these post-vaccination infections with Ct values of positive tests of unvaccinated patients. As viral loads could be associated with age and sex 9 , we assembled demographically-matched control groups of positive tests in unvaccinated patients with matching age group, sex and sampling date range (Methods). Comparing post-vaccination positive tests from days 1-11 (n=1,755) with their corresponding demographically-matched control group of the same size, we found no significant difference in the distribution of Ct values for any of the 3 genes (Figure 2a for RdRp, Extended Data Fig.…”
Beyond their substantial protection of individual vaccinees, it is hoped that the COVID-19 vaccines would reduce viral load in breakthrough infections thereby further suppress onward transmission. Here, analyzing positive SARS-CoV-2 test results following inoculation with the BNT162b2 mRNA vaccine, we find that the viral load is reduced 4-fold for infections occurring 12-28 days after the first dose of vaccine. These reduced viral loads hint to lower infectiousness, further contributing to vaccine impact on virus spread.
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