The First 100 Days of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Control in Vietnam
Authors: Thai Pham Quang , Rabaa Maia A , Luong Duong Huy , Tan Dang Quang , Quang Tran Dai , Quach Ha-Linh , Hoang Thi Ngoc-Anh , Dinh Phung Cong , Nghia Ngu Duy , Tu Tran Anh , Quang La Ngoc , Phuc Tran My , Chau Vinh , Khanh Nguyen Cong , Anh Dang Duc , Duong Tran Nhu , Thwaites Guy , van Doorn H Rogier , Choisy Marc ,   OUCRU COVID-19 Research Group, Chambers Mary , Choisy Marc , Day Jeremy , Trinh Dong Huu Khanh , Tam Dong Thi Hoai , Donovan Joseph , Duc Du Hong , Geskus Ronald B , Chanh Ho Quang , Van Hien Ho , Thao Huong Dang , Huy Huynh le Anh , Ha Huynh Ngan , Trieu Huynh Trung , Yen Huynh Xuan , Kestelyn Evelyne , Kesteman Thomas , Nguyet Lam Anh , Yen Lam Minh , Lawson Katrina , Thanh Le Kim , Nhu Le Nguyen Truc , Nhat Le Thanh Hoang , Lan Le Thi Hoang , Van Tan Le , Lewycka Sonia Odette , Tran Nguyen Bao , Nguyet Nguyen Minh , Quyen Nguyen Than Ha , Ngoc Nguyen Thanh , Ny Nguyen Thi Han , Thuong Nguyen Thi Hong , Trang Nguyen Thi Huyen , Tuyen Nguyen Thi Kim , Diep Nguyen Thi Ngoc , Dung Nguyen Thi Phuong , Tam Nguyen Thi , Hong Nguyen Thi Thu , Trang Nguyen Thu , Van Vinh Chau Nguyen , Truong Nguyen Xuan , Van Ninh Thi Thanh , Khanh Phan Nguyen Quoc , Lam Phung Khanh , Yen Phung Le Kim , Nhat Phung Tran Huy , Rabaa Maia , Thuong Thuong Nguyen Thuy , Thwaites Guy , Thwaites Louise , Phuc Tran My , Thanh Tran Tan , Ngoc Tran Thi Bich , Hien Tran Tinh , van Doorn H Rogier , van Nuil Jennifer , Chau Vinh , Bich Vu Thi Ngoc , Hang Vu Thi Ty , Yacoub Sophie 
Published: July 2020

Abstract

Background
One hundred days after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Vietnam on 23 January, 270 cases were confirmed, with no deaths. We describe the control measures used by the government and their relationship with imported and domestically acquired case numbers, with the aim of identifying the measures associated with successful SARS-CoV-2 control.

Methods
Clinical and demographic data on the first 270 SARS-CoV-2 infected cases and the timing and nature of government control measures, including numbers of tests and quarantined individuals, were analyzed. Apple and Google mobility data provided proxies for population movement. Serial intervals were calculated from 33 infector-infectee pairs and used to estimate the proportion of presymptomatic transmission events and time-varying reproduction numbers.

Results
A national lockdown was implemented between 1 and 22 April. Around 200 000 people were quarantined and 266 122 reverse transcription polymerase chain reaction (RT-PCR) tests conducted. Population mobility decreased progressively before lockdown. In total, 60% (163/270) of cases were imported; 43% (89/208) of resolved infections remained asymptomatic for the duration of infection. The serial interval was 3.24 days, and 27.5% (95% confidence interval [CI], 15.7%-40.0%) of transmissions occurred presymptomatically. Limited transmission amounted to a maximum reproduction number of 1.15 (95% CI, .·37–2.·36). No community transmission has been detected since 15 April.

Conclusions
Vietnam has controlled SARS-CoV-2 spread through the early introduction of mass communication, meticulous contact tracing with strict quarantine, and international travel restrictions. The value of these interventions is supported by the high proportion of asymptomatic and imported cases, and evidence for substantial presymptomatic transmission.