The Natural History and Transmission Potential of Asymptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Infection
Authors: Van Vinh Chau Nguyen , Lam Vo Thanh , Dung Nguyen Thanh , Yen Lam Minh , Minh Ngo Ngoc Quang , Hung Le Manh , Ngoc Nghiem My , Dung Nguyen Tri , Man Dinh Nguyen Huy , Nguyet Lam Anh , Nhat Le Thanh Hoang , Nhu Le Nguyen Truc , Ny Nguyen Thi Han , Hong Nguyen Thi Thu , Kestelyn Evelyne , Dung Nguyen Thi Phuong , Xuan Tran Chanh , Hien Tran Tinh , Phong Nguyen Thanh , Tu Tran Nguyen Hoang , Geskus Ronald B , Thanh Tran Tan , Truong Nguyen Thanh , Binh Nguyen Tan , Thuong Tang Chi , Thwaites Guy , Van Tan Le ,   Oxford University Clinical Research Unit COVID-19 Research Group, Van Vinh Chau Nguyen , Dung Nguyen Thanh , Hung Le Manh , Loan Huynh Thi , Truong Nguyen Thanh , Phong Nguyen Thanh , Man Dinh Nguyen Huy , Van Hao Nguyen , Thuy Duong Bich , Ngoc Nghiem My , Lan Nguyen Phu Huong , Thoa Pham Thi Ngoc , Thao Tran Nguyen Phuong , Phuong Tran Thi Lan , Uyen Le Thi Tam , Tam Tran Thi Thanh , That Bui Thi Ton , Nhung Huynh Kim , Tai Ngo Tan , Tu Tran Nguyen Hoang , Vuong Vo Trong , Ty Dinh Thi Bich , Dung Le Thi , Uyen Thai Lam , Tien Nguyen Thi My , Thao Ho Thi Thu , Thao Nguyen Ngoc , Vuong Huynh Ngoc Thien , Thao Pham Ngoc Phuong , Phuong Phan Minh , Tam Dong Thi Hoai , Kestelyn Evelyne , Joseph Donovan , Geskus Ronald , Thwaites Guy , van Doorn H Rogier , Van Hien Ho , Huy Huynh Le Anh , Ha Huynh Ngan , Yen Huynh Xuan , Van Nuil Jennifer , Day Jeremy , Donovan Joseph , Lawson Katrina , Nguyet Lam Anh , Yen Lam Minh , Nhu Le Nguyen Truc , Nhat Le Thanh Hoang , Van Tan Le , Odette Sonia Lewycka , Thwaites Louise , Rabaa Maia , Choisy Marc , Chambers Mary , Rahman Motiur , Hoa Ngo Thi , Nhien Nguyen Thanh Thuy , Ny Nguyen Thi Han , Tuyen Nguyen Thi Kim , Dung Nguyen Thi Phuong , Hong Nguyen Thi Thu , Truong Nguyen Xuan , Khanh Phan Nguyen Quoc , Yen Phung Le Kim , Yacoub Sophie , Kesteman Thomas , Thuong Nguyen Thuy Thuong , Thanh Tran Tan , Hien Tran Tinh , Hang Vu Thi Ty , Dung Nguyen Tri , Nga Le Hong 
Published: June 2020

Background

Little is known about the natural history of asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Methods

We conducted a prospective study at a quarantine center for coronavirus disease 2019 in Ho Chi Minh City, Vietnam. We enrolled quarantined people with reverse-transcription polymerase chain reaction (RT-PCR)–confirmed SARS-CoV-2 infection, collecting clinical data, travel and contact history, and saliva at enrollment and daily nasopharyngeal/throat swabs (NTSs) for RT-PCR testing. We compared the natural history and transmission potential of asymptomatic and symptomatic individuals.

Results

Between 10 March and 4 April 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. Seventeen (57%) participants imported cases. Compared with symptomatic individuals, asymptomatic people were less likely to have detectable SARS-CoV-2 in NTS collected at enrollment (8/13 [62%] vs 17/17 [100%]; P = .02). SARS-CoV-2 RNA was detected in 20 of 27 (74%) available saliva samples (7 of 11 [64%] in the asymptomatic group and 13 of 16 [81%] in the symptomatic group; P = .56). Analysis of RT-PCR positivity probability showed that asymptomatic participants had faster viral clearance than symptomatic participants (P &lt; .001 for difference over the first 19 days). This difference was most pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared to transmit SARS-CoV-2 to 4 contacts.

Conclusions

Asymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or NTSs. The NTS viral loads fall faster in asymptomatic individuals, but these individuals appear able to transmit the virus to others.