The latest research progress in asymptomatic and pre-symptomatic patients with COVID-19

The asymptomatic and pre-symptomatic infections of coronavirus disease 2019(COVID-19)has no perceptible clinical symptoms and signs,and it is not easy to be detected. The transmission of the virus carried by asymptomatic and pre-symptomatic patients is insidious,which brings great challenges to the control of the epidemic. Due to the length of the incubation period,some studies have failed to distinguish between asymptomatic and pre-symptomatic infections,resulting in a higher proportion of asymptomatic infections. This article reviews the latest research progress of characteristics,transmission,detection and control of asymptomatic and pre-symptomatic infection.

All five COVID-19 outbreaks during epidemic period of 2020/2021 in China were instigated by asymptomatic or pre-symptomatic individuals

Introduction:The significance of asymptomatic or pre-asymptomatic individuals in driving the COVID-19 epidemic in China or other countries remains uncertain.Method:We collected and analyzed all the epidemiologic and virological diagnostic details of the infected individuals released by public health authorities and reiterated every episode of outbreak on a timeline.All individuals associated with the five outbreaks had tested positive for SARS-CoV-2 infection.Results:In this study,all five COVID-19 outbreaks reported in China since October 2020 were analyzed.The Kashgar outbreak in Xinjiang province came into light for the first time on October 22,2020.However,it was initiated before October 11,2020,by a local asymptomatic import and export worker,who was infected at the working place.Subsequently,his wife caught the infection,which led to 430 more infections reported in the outbreak.The Beijing outbreak with 41 cases was noticed for the first time on December 22,2020.However,our analysis revealed that it was initiated by an asymptomatic individual from Indonesia on December 10,2020.The Shenyang outbreak,with 38 cases,noticed for the first time on December 23,2020,was initiated by a pre-symptomatic individual from South Korea on December 13,2020.Conclusion:The asymptomatic or pre-symptomatic individuals during the asymptomatic period were unsuspectingly infected by SARS-CoV-2,and unintentionally transmitted the virus to a large number of people.These findings suggest that early detection of asymptomatic or pre-symptomatic individuals is of critical importance in preventing future outbreaks or epidemics.

Asymptomatic and Pre-Symptomatic COVID-19 in China

As the novel coronavirus disease 2019(COVID-19)pandemic spreads rapidly across the globe many unanswered questions about the basic biology and epidemiology of the disease hamper our response strategies and limit our ability to achieve control and prevent a rebound or so-called“second wave”.One such crucial question is:To what degree do asymptomatic cases contribute to transmission?Early,small studies on this subject have found wide ranging estimates of the prevalence of asymptomatic carriers,and just a handful of studies so far have documented viral shedding by asymptomatic cases[1].We recently re-examined China’s COVID-19 case report data to investigate this question[2].This Editorial aims to describe how asymptomatic cases contribute to transmission and what the implications are for control strategies.

A comparative analysis of epidemiological characteristics of MERS-CoV and SARS-CoV-2 in Saudi Arabia

In this study,we determine and compare the incubation duration,serial interval,pre-symptomatic transmission,and case fatality rate of MERS-CoV and COVID-19 in Saudi Arabia based on contact tracing data we acquired in Saudi Arabia.The date of infection and infector-infectee pairings are deduced from travel history to Saudi Arabia or exposure to confirmed cases.The incubation times and serial intervals are estimated using parametric models accounting for exposure interval censoring.Our estimations show that MERS-CoV has a mean incubation time of 7.21(95%CI:6.59–7.85)days,whereas COVID-19(for the circulating strain in the study period)has a mean incubation period of 5.43(95%CI:4.81–6.11)days.MERS-CoV has an estimated serial interval of 14.13(95%CI:13.9–14.7)days,while COVID-19 has an estimated serial interval of 5.1(95%CI:5.0–5.5)days.The COVID-19 serial interval is found to be shorter than the incubation time,indicating that pre-symptomatic transmission may occur in a significant fraction of transmission events.We conclude that during the COVID-19 wave studied,at least 75%of transmission happened prior to the onset of symptoms.The CFR for MERS-CoV is estimated to be 38.1%(95%CI:36.8–39.5),while the CFR for COVID-191.67%(95%CI:1.63–1.71).This work is expected to help design future surveillance and intervention program targeted at specific respiratory virus outbreaks,and have implications for contingency planning for future coronavirus outbreaks.

Impact of asymptomatic COVID-19 carriers on pandemic policy outcomes

This paper provides a mathematical model that makes it clearly visible why the underestimation of r,the fraction of asymptomatic COVID-19 carriers in the general population,may lead to a catastrophic reliance on the standard policy intervention that attempts to isolate all confirmed infectious cases.The SE(AþO)R model with infectives separated into asymptomatic and ordinary carriers,supplemented by a model of the data generation process,is calibrated to standard early pandemic datasets for two countries.It is shown that certain fundamental parameters,critically r,are unidentifiable with this data.A general analytical framework is presented that projects the impact of different types of policy intervention.It is found that the lack of parameter identifiability implies that some,but not all,potential policy interventions can be correctly predicted.In an example representing Italy in March 2020,a hypothetical optimal policy of isolating confirmed cases that aims to reduce the basic reproduction number R0 of the outbreak from 4.4 to 0.8 assuming r¼0,only achieves 3.8 if it turns out that r¼40%.