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.

248 2 1 Main text: 2788 2 2 Running title: Asymptomatic SARS-CoV-2 infection 2 3 ABSTRACT 2 5 Background 2 6Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its 2 7 contribution to infection transmission. 2 8 Methods 2 9We conducted a prospective study at a quarantine centre for COVID-19 in Ho Chi Minh City, 3 0 Vietnam. We enrolled quarantined people with RT-PCR-confirmed SARS-CoV-2 infection, 3 1 collecting clinical data, travel and contact history, and saliva at enrolment and daily 3 2 nasopharyngeal throat swabs (NTS) for RT-PCR testing. We compared the natural history and 3 3 transmission potential of asymptomatic and symptomatic individuals.3 4 Results 3 5Between March 10 th and April 4 th , 2020, 14,000 quarantined people were tested for SARS-3 6CoV-2; 49 were positive. Of these, 30 participated in the study: 13(43%) never had symptoms 3 7 and 17(57%) were symptomatic. 17(57%) participants acquired their infection outside Vietnam. 3 8 Compared with symptomatic individuals, asymptomatic people were less likely to have 3 9 detectable SARS-CoV-2 in NTS samples collected at enrolment (8/13 (62%) vs. 17/17 (100%) 4 0 P=0.02). SARS-CoV-2 RNA was detected in 20/27 (74%) available saliva; 7/11 (64%) in the 4 1 asymptomatic and 13/16 (81%) in the symptomatic group (P=0.56). Analysis of the probability 4 2 of RT-PCR positivity showed asymptomatic participants had faster viral clearance than 4 3 symptomatic participants (P<0.001 for difference over first 19 days). This difference was most 4 4 pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared 4 5 to transmit the infection to up to four contacts. 4 6 Conclusions 4 7 Asymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or 4 8 NTS. NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit 4 9 the virus to others. 5 0 Hospitals, located approximately 60 km to the West and East, respectively, of HCMC (Figure 9 7 2A).

Cryptococcus neoformans ( C. neoformans var. grubii ) is an environmentally acquired pathogen causing 181,000 HIV-associated deaths each year. We sequenced 699 isolates, primarily C. neoformans from HIV-infected patients, from 5 countries in Asia and Africa. The phylogeny of C. neoformans reveals a recent exponential population expansion, consistent with the increase in the number of susceptible hosts. In our study population, this expansion has been driven by three sub-clades of the C. neoformans VNIa lineage; VNIa-4, VNIa-5 and VNIa-93. These three sub-clades account for 91% of clinical isolates sequenced in our study. Combining the genome data with clinical information, we find that the VNIa-93 sub-clade, the most common sub-clade in Uganda and Malawi, was associated with better outcomes than VNIa-4 and VNIa-5, which predominate in Southeast Asia. This study lays the foundation for further work investigating the dominance of VNIa-4, VNIa-5 and VNIa-93 and the association between lineage and clinical phenotype.

Background One hundred days after SARS-CoV-2 was first reported in Vietnam on January 23rd, 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 analysed. 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 pre-symptomatic transmission events and time-varying reproduction numbers. Results A national lockdown was implemented between April 1st and 22nd. Around 200 000 people were quarantined and 266 122 RT-PCR tests conducted. Population mobility decreased progressively before lockdown. 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, 15·7%-40·0%) of transmissions occurred pre-symptomatically. Limited transmission amounted to a maximum reproduction number of 1·15 (95% confidence interval, 0·37-2·36). No community transmission has been detected since April 15th. 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 pre-symptomatic transmission.