The Natural History and Transmission Potential of Asymptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Infection

Abstract

Background Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its contribution to infection transmission. Methods We conducted a prospective study at a quarantine center for COVID-19 in Ho Chi Minh City, Vietnam. We enrolled quarantined people with RT-PCR-confirmed SARS-CoV-2 infection, collecting clinical data, travel and contact history, and saliva at enrolment and daily nasopharyngeal throat swabs (NTS) for RT-PCR testing. We compared the natural history and transmission potential of asymptomatic and symptomatic individuals. Results Between March 10th and April 4th, 2020, 14,000 quarantined people were tested for SARS-CoV-2; 49 were positive. Of these, 30 participated in the study: 13(43%) never had symptoms and 17(57%) were symptomatic. 17(57%) participants acquired their infection outside Vietnam. Compared with symptomatic individuals, asymptomatic people were less likely to have detectable SARS-CoV-2 in NTS samples collected at enrolment (8/13 (62%) vs. 17/17 (100%) P=0.02). SARS-CoV-2 RNA was detected in 20/27 (74%) available saliva; 7/11 (64%) in the asymptomatic and 13/16 (81%) in the symptomatic group (P=0.56). Analysis of the probability of RT-PCR positivity showed asymptomatic participants had faster viral clearance than symptomatic participants (P<0.001 for difference over first 19 days). This difference was most pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared to transmit the infection to up to four contacts. Conclusions Asymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or NTS. NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit the virus to others.

Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis

“…The risks of bias, particularly those affecting selection of participants, differed between studies and could result in both underestimation and overestimation of the true proportion of asymptomatic infections. Also, we did not consider the possible impact of false negative RT-PCR results, which might be more likely to occur in asymptomatic infections [116] and would underestimate the proportion of asymptomatic infections [117]. The four databases that we searched are not comprehensive, but they cover the majority of publications and we do not believe that we have missed studies that would change our conclusions.…”

“…Integration of evidence from epidemiological, clinical, and laboratory studies will help to clarify the relative infectiousness of asymptomatic SARS-CoV-2. Studies using viral culture as well as RNA detection are needed, since RT-PCR defined viral loads appear to be broadly similar in asymptomatic and symptomatic people [116,125]. Age might play a role as children appear more likely than adults to have an asymptomatic course of infection (Fig 1) [126]; age was poorly reported in studies included in this review (Table 1).…”

Immunological considerations for COVID-19 vaccine strategies

“…It is particularly relevant to understand the difference in immune responses between asymptomatic, mild and severe cases and at early and late stages of infection, and to understand why seniors are particularly susceptible to COVID-19, whereas the young are better protected. It is estimated that 40-75% of infections may be mild or asymptomatic 7,8 and asymptomatic individuals may have a significantly longer duration of viral shedding than their symptomatic counterparts 9 . Furthermore, that asymptomatic and mildly ill individuals seem to develop low levels of antibody-mediated immunity has important implications for understanding herd immunity.…”

Increasing Temperature and Relative Humidity Accelerates Inactivation of SARS-CoV-2 on Surfaces

“…More broadly, viral persistence under indoor conditions is complex and may be driven by many factors, including surface type, temperature, relative humidity (RH), and matrix (e.g., bodily fluids) (8)(9)(10)(11)(12). Here, we report the first analysis of the stability of SARS-CoV-2 in simulated saliva, to represent a relevant clinical matrix (13,14), using droplets of various sizes deposited on surfaces and incubated under a range of controlled temperature and RH conditions, thereby providing a more complete understanding of factors that influence SARS-CoV-2 environmental persistence.…”