Investigating the Impact of Asymptomatic Carriers on COVID-19 Transmission (original) (raw)
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COVID-19: Need of the hour to revisit asymptomatic prevalence of coronavirus pandemic
Borneo Epidemiology Journal, 2020
Since the Coronavirus disease 2019 (COVID-19) pandemic unfolded in China (Huang et al., 2020) back in December 2019, thus far, more than five million people were infected with the virus and 333,401 death were recorded worldwide (WHO, 2020b). The exponential increase in number shows that COVID-19 spreads faster compared to Severe Acute Respiratory Syndrome (SARS) or Middle East Respiratory Syndrome (MERS). A study (Zou et al., 2020) has shown that high viral loads of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are detected in symptomatic patients soon after the onset of symptoms, wherein the load content is higher in their nose than in their throat. Furthermore, the same study has revealed similar viral loads between symptomatic and asymptomatic patients. Therefore, these findings may suggest the possibility of COVID-19 transmission earlier before the onset of symptoms itself. In the early stages of the pandemic, the control measures carried out have focused on screening of symptomatic person; at the time, the whole world thought that the spread of SARS-Cov-2 would only occur through symptomatic person-to-person transmission. In comparison, transmission in SARS would happen after the onset of illness, whereby the viral loads in the respiratory tract peaked around ten days after the development of symptoms by patients (Peiris et al., 2003). However, case detection for SARS (i.e. screening of symptomatic persons) will be grossly inadequate for the current COVID-19 pandemic, thus requiring different strategies to detect those infected with SARS-CoV-2 before they develop the symptoms.
Global Variation in the Basic Reproduction Number of COVID-19
Academia Letters, 2021
The rapid spread of the COVID-19 pandemic caught the world unprepared. The World Health Organisation released a statement on 9 January 2020 reporting that a novel respiratory disease had been identified by Chinese authorities, originating in Wuhan [1]. By 17 January, China recorded 62 cases, and 3 travellers had exported the disease, with two diagnosed in Thailand and one in Japan [2]. At the time of writing, 219 countries have been affected by the disease, with the total death toll estimated at over 2 100 000 [3]. The need to understand the dynamics of disease transmission is crucial in order to combat it effectively. The basic reproduction number (R0) is the average number of susceptible individuals that are infected by a single infected individual [4], and is a critical parameter for modelling disease transmission [5]. It is best measured in the early phase of the outbreak, before control measures have had time to take effect, and when most of the population is susceptible. Herein, we investigated and visualised the spatial variability in estimates of R0 obtained at the start of the pandemic by conducting a systematic literature review. We further explored the relationship
The big unknown: The asymptomatic spread of COVID-19
BIOMATH, 2020
The paper draws attention to the asymptomatic and mildly symptomatic cases of COVID-19, which, according to some reports, may constitute a large fraction of the infected individuals. These cases are often unreported and are not captured in the total number of confirmed cases communicated daily. On the one hand, this group may play a significant role in the spread of the infection, as asymptomatic cases are seldom detected and quarantined. On the other hand, it may play a significant role in disease extinction by contributing to the development of sufficient herd immunity.
Revista da Sociedade Brasileira de Medicina Tropical
In the absence of vaccines and effective antiviral drugs, control of the spread of coronavirus disease (Covid-19) relies mainly on the adequacy of public health resources and policies. Hence, failure to establish and implement scientifically reliable control measures may have a significant effect on the incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, severity of the disease, and death toll. The average number of secondary transmissions from an infected person, or reproduction numbers (R 0 and R), and the points at which the collective immunity begins to reduce the transmission of the infection, or herd immunity thresholds, are important epidemiological tools used in strategies of Covid-19 control, suppression, and mitigation. However, SARS-CoV-2 transmission through asymptomatic carriers and, possibly, aerosols, has been ignored, and this may affect the effectiveness of Covid-19 control strategies. Therefore, consideration of the two possible ways of transmission would substantially increase the values of reproduction numbers, but if estimates of the contingent of the population naturally resistant to the virus, plus those with pre-existing cross-immunity to SARS-CoV-2 were considered, the evaluation of herd immunity thresholds should reach their real and achievable levels.
The unmitigated profile of COVID-19 infectiousness
2021
Quantifying the temporal dynamics of infectiousness of individuals infected with SARS-CoV-2 is crucial for understanding the spread of the COVID-19 pandemic and for analyzing the effectiveness of different mitigation strategies. Many studies have tried to use data from the onset of symptoms of infector-infectee pairs to estimate the infectiousness profile of SARS-CoV-2. However, both statistical and epidemiological biases in the data could lead to an underestimation of the duration of infectiousness. We correct for these biases by curating data from the initial outbreak of the pandemic in China (when mitigation steps were still minimal), and find that the infectiousness profile is wider than previously thought. For example, our estimate for the proportion of transmissions occurring 14 days or more after infection is an order of magnitude higher - namely 19% (95% CI 10%-25%). The inferred generation interval distribution is sensitive to the definition of the period of unmitigated tra...
2020
Coronavirus disease 2019 (COVID-19) is a novel human respiratory disease caused by the SARS-CoV-2 virus. Asymptomatic carriers of the COVID-19 virus display no clinical symptoms but are known to be contagious. Recent evidence reveals that this subpopulation, as well as persons with mild disease, are a major contributor in the propagation of the disease. The rapid spread of COVID-19 forced governments around the world to establish and enforce generalized risk mitigation strategies, from lockdowns to guidelines for social distancing, in an effort to minimize community transmission. This created an unprecedented epidemiological situation not properly characterized by existing mathematical models of isolation and quarantine. In this manuscript, we present a mathematical model for community transmission of COVID-19 taking into account asymptomatic carriers and varying degrees of risk mitigation. The main results consist of an exact calculation of the effective reproduction number , and a...
Covid19 Pandemic, Closing Gaps in the Responses and Transmission Chain Events
2020
Background: Emerging and reemerging pathogens are global challenges for public health.1 Coronaviruses are enveloped RNA viruses that are distributed broadly among humans, other mammals, and birds and that cause respiratory, enteric, hepatic, and neurologic diseases. the high prevalence and wide distribution of coronaviruses, the large genetic diversity and frequent recombination of their genomes, and increasing human–animal interface activities, novel coronaviruses are likely to emerge periodically in humans owing to frequent cross-species infections and occasional spillover event. Objectives: To study the short-term morbidities and mortalities and international spread time trends of the N Corona Virus 2019 outbreak, to study, to study the explosiveness and aggressiveness of the outbreak and the gaps in response. Methodology: Outbreak events follow up and observation study over two months has been carried out through daily statistical reports issuing by world health organizations as...
A quantitative compendium of COVID-19 epidemiology
arXiv: Other Quantitative Biology, 2020
Accurate numbers are needed to understand and predict viral dynamics. Curation of high-quality literature values for the infectious period duration or household secondary attack rate, for example, is especially pressing currently because these numbers inform decisions about how and when to lockdown or reopen societies. We aim to provide a curated source for the key numbers that help us understand the virus driving our current global crisis. This compendium focuses solely on COVID-19 epidemiology. The numbers reported in summary format are substantiated by annotated references. For each property, we provide a concise definition, description of measurement and inference methods, and associated caveats. We hope this compendium will make essential numbers more accessible and avoid common sources of confusion for the many newcomers to the field such as using the incubation period to denote and quantify the latent period or using the hospitalization duration for the infectiousness period ...