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1.
Kidney360 ; 2(12): 1917-1927, 2021 12 30.
Article in English | MEDLINE | ID: covidwho-1789955

ABSTRACT

Background: Patients with ESKD on maintenance dialysis receive dialysis in common spaces with other patients and have a higher risk of severe SARS-CoV-2 infections. They may have persistently or intermittently positive SARS-CoV-2 RT-PCR tests after infection. We describe the clinical course of SARS-CoV-2 infection and the serologic response in a convenience sample of patients with ESKD to understand the duration of infectivity. Methods: From August to November 2020, we enrolled patients on maintenance dialysis with SARS-CoV-2 infections from outpatient dialysis facilities in Atlanta, Georgia. We followed participants for approximately 42 days. We assessed COVID-19 symptoms and collected specimens. Oropharyngeal (OP), anterior nasal (AN), and saliva (SA) specimens were tested for the presence of SARS-CoV-2 RNA, using RT-PCR, and sent for viral culture. Serology, including neutralizing antibodies, was measured in blood specimens. Results: Fifteen participants, with a median age of 58 (range, 37‒77) years, were enrolled. Median duration of RT-PCR positivity from diagnosis was 18 days (interquartile range [IQR], 8‒24 days). Ten participants had at least one, for a total of 41, positive RT-PCR specimens ≥10 days after symptoms onset. Of these 41 specimens, 21 underwent viral culture; one (5%) was positive 14 days after symptom onset. Thirteen participants developed SARS-CoV-2-specific antibodies, 11 of which included neutralizing antibodies. RT-PCRs remained positive after seroconversion in eight participants and after detection of neutralizing antibodies in four participants; however, all of these samples were culture negative. Conclusions: Patients with ESKD on maintenance dialysis remained persistently and intermittently SARS-CoV-2-RT-PCR positive. However, of the 15 participants, only one had infectious virus, on day 14 after symptom onset. Most participants mounted an antibody response, including neutralizing antibodies. Participants continued having RT-PCR-positive results in the presence of SARS-CoV-2-specific antibodies, but without replication-competent virus detected.


Subject(s)
COVID-19 , Adult , Aged , Antibodies, Neutralizing , Antibodies, Viral , COVID-19/complications , Humans , Middle Aged , Outpatients , RNA, Viral , Renal Dialysis , SARS-CoV-2
2.
Vaccine ; 40(22): 3027-3037, 2022 May 11.
Article in English | MEDLINE | ID: covidwho-1783823

ABSTRACT

BACKGROUND: During the first half of 2021, we observed high vaccine effectiveness (VE) against SARS-CoV2-infection. The replacement of the alpha-'variant of concern' (VOC) by the delta-VOC and uncertainty about the time course of immunity called for a re-assessment. METHODS: We estimated VE against transmission of infection (VET) from Belgian contact tracing data for high-risk exposure contacts between 26/01/2021 and 14/12/2021 by susceptibility (VEs) and infectiousness of breakthrough cases (VEi) for a complete schedule of Ad26.COV2.S, ChAdOx1, BNT162b2, mRNA-1273 as well as infection-acquired and hybrid immunity. We used a multilevel Bayesian model and adjusted for personal characteristics (age, sex, household), background exposure, calendar week, VOC and time since immunity conferring-event. FINDINGS: VET-estimates were higher for mRNA-vaccines, over 90%, compared to viral vector vaccines: 66% and 80% for Ad26COV2.S and ChAdOx1 respectively (Alpha, 0-50 days after vaccination). Delta was associated with a 40% increase in odds of transmission and a decrease of VEs (72-64%) and especially of VEi (71-46% for BNT162b2). Infection-acquired and hybrid immunity were less affected by Delta. Waning further reduced VET-estimates: from 81% to 63% for BNT162b2 (Delta, 150-200 days after vaccination). We observed lower initial VEi in the age group 65-84 years (32% vs 46% in the age group 45-64 years for BNT162b2) and faster waning. Hybrid immunity waned slower than vaccine-induced immunity. INTERPRETATION: VEi and VEs-estimates, while remaining significant, were reduced by Delta and waned over time. We observed faster waning in the oldest age group. We should seek to improve vaccine-induced protection in older persons and those vaccinated with viral-vector vaccines.


Subject(s)
COVID-19 , Vaccines , Aged , Aged, 80 and over , Bayes Theorem , Belgium/epidemiology , COVID-19/prevention & control , Contact Tracing , Humans , Middle Aged , RNA, Viral , SARS-CoV-2 , Vaccination
3.
Euro Surveill ; 27(8)2022 02.
Article in English | MEDLINE | ID: covidwho-1714940

ABSTRACT

BackgroundSARS-CoV-2 RT-PCR assays are more sensitive than rapid antigen detection assays (RDT) and can detect viral RNA even after an individual is no longer infectious. RDT can reduce the time to test and the results might better correlate with infectiousness.AimWe assessed the ability of five RDT to identify infectious COVID-19 cases and systematically recorded the turnaround time of RT-PCR testing.MethodsSensitivity of RDT was determined using a serially diluted SARS-CoV-2 stock with known viral RNA concentration. The probability of detecting infectious virus at a given viral load was calculated using logistic regression of viral RNA concentration and matched culture results of 78 specimens from randomly selected non-hospitalised cases. The probability of each RDT to detect infectious cases was calculated as the sum of the projected probabilities for viral isolation success for every viral RNA load found at the time of diagnosis in 1,739 confirmed non-hospitalised COVID-19 cases.ResultsThe distribution of quantification cycle values and estimated RNA loads for patients reporting to drive-through testing was skewed to high RNA loads. With the most sensitive RDT (Abbott and SD Biosensor), 97.30% (range: 88.65-99.77) of infectious individuals would be detected. This decreased to 92.73% (range: 60.30-99.77) for Coris BioConcept and GenBody, and 75.53% (range: 17.55-99.77) for RapiGEN. Only 32.9% of RT-PCR results were available on the same day as specimen collection.ConclusionThe most sensitive RDT detected infectious COVID-19 cases with high sensitivity and may considerably improve containment through more rapid isolation and contact tracing.


Subject(s)
COVID-19 , SARS-CoV-2 , Antigens, Viral/analysis , COVID-19/diagnosis , COVID-19/epidemiology , COVID-19 Testing , Humans , Netherlands/epidemiology , SARS-CoV-2/genetics , Sensitivity and Specificity
4.
Clin Infect Dis ; 73(9): e3456-e3458, 2021 11 02.
Article in English | MEDLINE | ID: covidwho-1705023
5.
Open Forum Infect Dis ; 9(1): ofab600, 2022 Jan.
Article in English | MEDLINE | ID: covidwho-1700044

ABSTRACT

We developed a simple, noninvasive mask sampling method to quantify and sequence severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from exhaled breath. We found substantial variation between individuals in SARS-CoV-2 copies exhaled over a 15-minute period, which moderately correlated with nasal swab viral load. Talking was associated with a median of 2 log10 greater exhaled viral copies. Exposure varies substantially between individuals but may be risk stratified by nasal swab viral load and whether the exposure involved conversation.

6.
Matter ; 5(2): 694-709, 2022 Feb 02.
Article in English | MEDLINE | ID: covidwho-1670871

ABSTRACT

The current COVID-19 pandemic urges us to develop ultra-sensitive surface-enhanced Raman scattering (SERS) substrates to identify the infectiousness of SARS-CoV-2 virions in actual environments. Here, a micrometer-sized spherical SnS2 structure with the hierarchical nanostructure of "nano-canyon" morphology was developed as semiconductor-based SERS substrate, and it exhibited an extremely low limit of detection of 10-13 M for methylene blue, which is one of the highest sensitivities among the reported pure semiconductor-based SERS substrates. Such ultra-high SERS sensitivity originated from the synergistic enhancements of the molecular enrichment caused by capillary effect and the charge transfer chemical enhancement boosted by the lattice strain and sulfur vacancies. The novel two-step SERS diagnostic route based on the ultra-sensitive SnS2 substrate was presented to diagnose the infectiousness of SARS-CoV-2 through the identification standard of SERS signals for SARS-CoV-2 S protein and RNA, which could accurately identify non-infectious lysed SARS-CoV-2 virions in actual environments, whereas the current PCR methods cannot.

8.
Proc Natl Acad Sci U S A ; 118(49)2021 12 07.
Article in English | MEDLINE | ID: covidwho-1550424

ABSTRACT

The within-host viral kinetics of SARS-CoV-2 infection and how they relate to a person's infectiousness are not well understood. This limits our ability to quantify the impact of interventions on viral transmission. Here, we develop viral dynamic models of SARS-CoV-2 infection and fit them to data to estimate key within-host parameters such as the infected cell half-life and the within-host reproductive number. We then develop a model linking viral load (VL) to infectiousness and show a person's infectiousness increases sublinearly with VL and that the logarithm of the VL in the upper respiratory tract is a better surrogate of infectiousness than the VL itself. Using data on VL and the predicted infectiousness, we further incorporated data on antigen and RT-PCR tests and compared their usefulness in detecting infection and preventing transmission. We found that RT-PCR tests perform better than antigen tests assuming equal testing frequency; however, more frequent antigen testing may perform equally well with RT-PCR tests at a lower cost but with many more false-negative tests. Overall, our models provide a quantitative framework for inferring the impact of therapeutics and vaccines that lower VL on the infectiousness of individuals and for evaluating rapid testing strategies.


Subject(s)
COVID-19/diagnosis , SARS-CoV-2/genetics , COVID-19/virology , COVID-19 Nucleic Acid Testing/methods , False Positive Reactions , Humans , Kinetics , Serologic Tests/methods
9.
Philos Trans A Math Phys Eng Sci ; 380(2214): 20210124, 2022 Jan 10.
Article in English | MEDLINE | ID: covidwho-1528261

ABSTRACT

Prolonged school closure has been adopted worldwide to control COVID-19. Indeed, UN Educational, Scientific and Cultural Organization figures show that two-thirds of an academic year was lost on average worldwide due to COVID-19 school closures. Such pre-emptive implementation was predicated on the premise that school children are a core group for COVID-19 transmission. Using surveillance data from the Chinese cities of Shenzhen and Anqing together, we inferred that compared with the elderly aged 60 and over, children aged 18 and under and adults aged 19-59 were 75% and 32% less susceptible to infection, respectively. Using transmission models parametrized with synthetic contact matrices for 177 jurisdictions around the world, we showed that the lower susceptibility of school children substantially limited the effectiveness of school closure in reducing COVID-19 transmissibility. Our results, together with recent findings that clinical severity of COVID-19 in children is lower, suggest that school closure may not be ideal as a sustained, primary intervention for controlling COVID-19. This article is part of the theme issue 'Data science approach to infectious disease surveillance'.


Subject(s)
COVID-19 , Aged , Child , Humans , Middle Aged , SARS-CoV-2 , Schools
10.
Radiologe ; 61(10): 880-887, 2021 Oct.
Article in German | MEDLINE | ID: covidwho-1427228

ABSTRACT

Mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can enhance the spread and the infectiousness and decrease the protective effect of antibodies present after infection, vaccination or antibody treatment. The alpha variant (B.1.1.7), first seen in Kent/United Kingdom, has increased the R­value and therefore the infectiousness by 75%; however, the effectiveness of the vaccines against SARS-CoV­2 available in Germany seems to be only slightly impaired by these mutations. In the case of the beta variant (B.1.351), first described in South Africa, the neutralization ability of antibodies towards SARS-CoV­2 is decreased. The monoclonal antibodies bamlanivimab and etesivimab, which are used therapeutically, are ineffective. The AstraZeneca vaccine offers almost no protection against mild or moderate disease caused by the beta variant. The gamma variant (P.1 or B.1.1.28.1), which was first found in Brazil, is probably 1.7-2.6 times more transmissible than previous virus strains circulating in Brazil. In addition to the infectiousness, the mortality risk of the gamma variant also seems to be increased between 1.2 and 1.9-fold in adults and between 5 and 8-fold in young persons. The delta variant (B.1.617), first described in India, is now dominant in most countries. It is 50% more infectious than the alpha variant, and the protective effect of vaccinations against symptomatic disease can be decreased (Biontech: delta variant 88%, alpha variant 93.7%; AstraZeneca: delta variant 67%, alpha variant 74.5%). Furthermore, the course of the disease with the delta variant is often more severe than with the wild type. Disease courses with the delta variant are less severe in vaccinated than in nonvaccinated persons, and fatal outcomes are substantially rarer. A high vaccination rate is essential in order to approach herd immunity and to bring the pandemic under control. Even where the protective effect towards mild or moderate disease is decreased, as a rule, vaccination still offers excellent protection against life-threatening and fatal disease courses.


Subject(s)
COVID-19 , Adult , COVID-19 Vaccines , Humans , Mutation , SARS-CoV-2
11.
J R Soc Interface ; 18(174): 20200756, 2021 01.
Article in English | MEDLINE | ID: covidwho-1383292

ABSTRACT

The timing of transmission plays a key role in the dynamics and controllability of an epidemic. However, observing generation times-the time interval between the infection of an infector and an infectee in a transmission pair-requires data on infection times, which are generally unknown. The timing of symptom onset is more easily observed; generation times are therefore often estimated based on serial intervals-the time interval between symptom onset of an infector and an infectee. This estimation follows one of two approaches: (i) approximating the generation time distribution by the serial interval distribution or (ii) deriving the generation time distribution from the serial interval and incubation period-the time interval between infection and symptom onset in a single individual-distributions. These two approaches make different-and not always explicitly stated-assumptions about the relationship between infectiousness and symptoms, resulting in different generation time distributions with the same mean but unequal variances. Here, we clarify the assumptions that each approach makes and show that neither set of assumptions is plausible for most pathogens. However, the variances of the generation time distribution derived under each assumption can reasonably be considered as upper (approximation with serial interval) and lower (derivation from serial interval) bounds. Thus, we suggest a pragmatic solution is to use both approaches and treat these as edge cases in downstream analysis. We discuss the impact of the variance of the generation time distribution on the controllability of an epidemic through strategies based on contact tracing, and we show that underestimating this variance is likely to overestimate controllability.


Subject(s)
COVID-19/epidemiology , COVID-19/transmission , Contact Tracing , Models, Biological , SARS-CoV-2 , Humans , Time Factors
12.
J Clin Microbiol ; 59(9): e0089621, 2021 08 18.
Article in English | MEDLINE | ID: covidwho-1365131

ABSTRACT

The identification and isolation of highly infectious SARS-CoV-2-infected individuals is an important public health strategy. Rapid antigen detection tests (RADT) are promising tools for large-scale screenings due to timely results and feasibility for on-site testing. Nonetheless, the diagnostic performance of RADT in detecting infectious individuals is not yet fully determined. In this study, RT-qPCR and virus culture of RT-qPCR-positive samples were used to evaluate and compare the performance of the Standard Q COVID-19 Ag test in detecting SARS-CoV-2-infected and possibly infectious individuals. To this end, two combined oro- and nasopharyngeal swabs were collected at a routine SARS-CoV-2 diagnostic center. A total of 2,028 samples were tested, and 118 virus cultures were inoculated. SARS-CoV-2 infection was detected in 210 samples by RT-qPCR, representing a positive rate of 10.36%. The Standard Q COVID-19 Ag test yielded a positive result in 92 (4.54%) samples resulting in an overall sensitivity and specificity of 42.86 and 99.89%, respectively. For adjusted CT values of <20 (n = 14), <25 (n = 57), and <30 (n = 88), the RADT reached sensitivities of 100, 98.25, and 88.64%, respectively. All 29 culture-positive samples were detected by the RADT. Although the overall sensitivity was low, the Standard Q COVID-19 Ag test reliably detected patients with high RNA loads. In addition, negative RADT results fully corresponded with the lack of viral cultivability in Vero E6 cells. These results indicate that RADT can be a valuable tool for the detection of individuals with high RNA loads that are likely to transmit SARS-CoV-2.


Subject(s)
COVID-19 , Communicable Diseases , Humans , Real-Time Polymerase Chain Reaction , SARS-CoV-2 , Sensitivity and Specificity
13.
BMC Med Res Methodol ; 21(1): 165, 2021 08 10.
Article in English | MEDLINE | ID: covidwho-1352645

ABSTRACT

BACKGROUND: A considerable proportion of SARS-CoV-2 transmission occurs from asymptomatic and pre-symptomatic cases. Therefore, different polymerase chain reaction (PCR)- or rapid antigen test (RAT)-based approaches are being discussed and applied to identify infectious individuals that would have otherwise gone undetected. In this article, we provide a framework to estimate the time-dependent risk of being infectious after a negative SARS-CoV-2 test, and we simulate the number of expected infectious individuals over time in populations who initially tested negative. METHODS: A Monte Carlo approach is used to simulate asymptomatic infections over a 10-days period in populations of 1000 individuals following a negative SARS-CoV-2 test. Parameters representing the application of PCR tests or RATs are utilized, and SARS-CoV-2 cumulative 7-day incidences between 25 and 200 per 100,000 people are considered. Simulation results are compared to case numbers predicted via a mathematical equation. RESULTS: The simulations showed a continuous increase in infectious individuals over time in populations of individuals who initially tested SARS-CoV-2 negative. The interplay between false negative rates of PCR tests or RATs, and the time that has passed since testing determines the number of infectious individuals. The simulated and the mathematically predicted number of infectious individuals were comparable. However, Monte Carlo simulations highlight that, due to random variation, theoretically observed infectious individuals can considerably exceed predicted case numbers even shortly after a test was conducted. CONCLUSIONS: This study demonstrates that the number of infectious individuals in a screened group of asymptomatic people can be effectively reduced, and this effect can be described mathematically. However, the false negative rate of a test, the time since the negative test and the underlying SARS-CoV-2 incidence are critical parameters in determining the observed subsequent number of cases in tested population groups.


Subject(s)
COVID-19 , Communicable Diseases , Computer Simulation , Humans , Polymerase Chain Reaction , SARS-CoV-2
14.
Int J Infect Dis ; 111: 5-9, 2021 Oct.
Article in English | MEDLINE | ID: covidwho-1351714

ABSTRACT

OBJECTIVE: The aim of this study was to investigate the infectiousness of re-positive coronavirus disease 2019 (COVID-19) patients. METHODS: All nucleic acid testing (NAT) was performed using throat swabs, nasopharyngeal swabs, and anal swabs, which were tested by Fluorescent quantitative realtime PCR. Re-positive cases were defined as a discharged patient who re-tested positive by NAT. Micro-neutralization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was performed based on the methods for severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) viruses. IgM and IgG against the N protein of SARS-CoV-2 were determined by ELISA. RESULTS: A total 255 (16.04%) of 1590 COVID-19 patients were re-positive. The re-positive cases were more likely to occur in patients in the 20-39 years age group and in patients with disease of moderate severity. Quantitative PCR showed that cycle threshold (Ct) values and viral loads were both far lower than in the hospitalized COVID-19 patients. The viral load in re-positive cases was very low. Viral culture of the samples from re-positive patients showed no cytopathic effect, and NAT of the culture medium of viral cultures all exhibited negative results. CONCLUSION: The viral load in re-positive cases was very low; patients were not infectious and the risk of human-to-human transmission was extremely low. Discharged COVID-19 patients should undergo home health management for 3 weeks.


Subject(s)
COVID-19 , Humans , Real-Time Polymerase Chain Reaction , SARS-CoV-2 , Serologic Tests , Viral Load
15.
Open Forum Infect Dis ; 8(7): ofab350, 2021 Jul.
Article in English | MEDLINE | ID: covidwho-1331567

ABSTRACT

To identify the temporal change in the possible risk of superspreading events, we estimated the overdispersion parameter in 2 different periods of the coronavirus disease 2019 pandemic. We determined that the possible risk of superspreading events was reduced 90% during the second epidemic period in South Korea.

17.
Open Forum Infect Dis ; 8(7): ofab310, 2021 Jul.
Article in English | MEDLINE | ID: covidwho-1322651

ABSTRACT

BACKGROUND: Given the persistence of viral RNA in clinically recovered coronavirus disease 2019 (COVID-19) patients, subgenomic RNAs (sgRNAs) have been reported as potential molecular viability markers for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, few data are available on their longitudinal kinetics, compared with genomic RNA (gRNA), in clinical samples. METHODS: We analyzed 536 samples from 205 patients with COVID-19 from placebo-controlled, outpatient trials of peginterferon Lambda-1a (Lambda; n = 177) and favipiravir (n = 359). Nasal swabs were collected at 3 time points in the Lambda (days 1, 4, and 6) and favipiravir (days 1, 5, and 10) trials. N-gene gRNA and sgRNA were quantified by quantitative reverse transcription polymerase chain reaction. To investigate the decay kinetics in vitro, we measured gRNA and sgRNA in A549ACE2+ cells infected with SARS-CoV-2, following treatment with remdesivir or dimethylsulfoxide control. RESULTS: At 6 days in the Lambda trial and 10 days in the favipiravir trial, sgRNA remained detectable in 51.6% (32/62) and 49.5% (51/106) of the samples, respectively. Cycle threshold (Ct) values for gRNA and sgRNA were highly linearly correlated (marginal R 2 = 0.83), and the rate of increase did not differ significantly in the Lambda trial (1.36 cycles/d vs 1.36 cycles/d; P = .97) or the favipiravir trial (1.03 cycles/d vs 0.94 cycles/d; P = .26). From samples collected 15-21 days after symptom onset, sgRNA was detectable in 48.1% (40/83) of participants. In SARS-CoV-2-infected A549ACE2+ cells treated with remdesivir, the rate of Ct increase did not differ between gRNA and sgRNA. CONCLUSIONS: In clinical samples and in vitro, sgRNA was highly correlated with gRNA and did not demonstrate different decay patterns to support its application as a viability marker.

18.
Euro Surveill ; 26(21)2021 05.
Article in English | MEDLINE | ID: covidwho-1247780

ABSTRACT

We investigated three SARS-CoV-2 variant B.1.1.7 childcare centre and related household outbreaks. Despite group cohorting, cases occurred in almost all groups, i.e. also among persons without close contact. Children's secondary attack rates (SAR) were similar to adults (childcare centres: 23% vs 30%; p = 0.15; households: 32% vs 39%; p = 0.27); child- and adult-induced household outbreaks also led to similar SAR. With the advent of B.1.1.7, susceptibility and infectiousness of children and adults seem to converge. Public health measures should be revisited accordingly.


Subject(s)
COVID-19 , SARS-CoV-2 , Adult , Child , Disease Outbreaks , Germany/epidemiology , Humans
19.
J Infect Chemother ; 27(8): 1273-1275, 2021 Aug.
Article in English | MEDLINE | ID: covidwho-1225293

ABSTRACT

Rapid antigen tests (RATs) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have advantages over viral culture in terms of cost and rapidity of testing, but they have low sensitivity. In addition, RATs tend to be negative from approximately 11 days after symptom onset. To determine whether the antigen-negative state indicates a lack of infectiousness, we assessed the association between viral culture and RAT results. Viral culture, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and rapid antigen testing were performed on stored nasopharyngeal samples with threshold cycle values < 30, based on previous RT-qPCR testing. SARS-CoV-2 was isolated by viral culture from nine samples (45%) and one sample (17%) with positive and negative RAT results, respectively. The RAT and viral culture results were both associated with the viral load level and their cutoffs were similar, but the associations were not statistically significant. RAT might be a useful indicator of infectiousness, which can be helpful to control infection. However, further studies with larger sample size are warranted to confirm this observation.


Subject(s)
COVID-19 , SARS-CoV-2 , Humans , Nasopharynx , Sensitivity and Specificity , Serologic Tests
20.
Elife ; 102021 04 26.
Article in English | MEDLINE | ID: covidwho-1201638

ABSTRACT

Background: Understanding changes in infectiousness during SARS-COV-2 infections is critical to assess the effectiveness of public health measures such as contact tracing. Methods: Here, we develop a novel mechanistic approach to infer the infectiousness profile of SARS-COV-2-infected individuals using data from known infector-infectee pairs. We compare estimates of key epidemiological quantities generated using our mechanistic method with analogous estimates generated using previous approaches. Results: The mechanistic method provides an improved fit to data from SARS-CoV-2 infector-infectee pairs compared to commonly used approaches. Our best-fitting model indicates a high proportion of presymptomatic transmissions, with many transmissions occurring shortly before the infector develops symptoms. Conclusions: High infectiousness immediately prior to symptom onset highlights the importance of continued contact tracing until effective vaccines have been distributed widely, even if contacts from a short time window before symptom onset alone are traced. Funding: Engineering and Physical Sciences Research Council (EPSRC).


The risk of a person with COVID-19 spreading the SARS-CoV-2 virus that causes it to others varies over the course of their infection. Transmission depends both on how much virus is in the infected person's airway and their behaviors, such as whether they wear a mask and how many people they have contact with. Learning more about when people are most infectious would help public health officials stop the spread of the virus. For example, officials can then introduce policies that ensure that people are isolated when they are most infectious. The majority of studies assessing when people with COVID-19 are most infectious so far have assumed that transmission is not linked to when symptoms appear. But that may not be true. After people develop symptoms, they may be more likely to stay home, avoid others, or take other measures that prevent transmission. Using computer modeling and data from previous studies of individuals who infected others with SARS-CoV-2, Hart et al. show that about 65% of virus transmission occurs before symptoms develop. In fact, the computational experiments show the risk of transmission is highest immediately before symptoms develop. This highlights the importance of identifying people exposed to someone infected with the virus and isolating potential recipients before they develop symptoms. This information may help public health officials develop more effective strategies to prevent the spread of SARS-CoV-2. It may also help scientists develop more accurate models to predict the spread of the virus. However, the computational experiments used data on infections early in the pandemic that may not reflect the current situation. Changes in public health policy, the behavior of individuals and the appearance of new strains of SARS-CoV-2, all affect the timing of transmission. As more recent data become available, Hart et al. plan to explore how characteristics of transmission have changed as the pandemic has progressed.


Subject(s)
COVID-19/transmission , Contact Tracing/methods , COVID-19/epidemiology , Carrier State/epidemiology , Carrier State/transmission , Health Policy , Humans , Models, Theoretical , Public Health , Risk Factors , SARS-CoV-2
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