We sampled nasal–pharyngeal throat swabs from 96,123 asymptomatic individuals at risk of SARS-CoV-2 infection, and generated 22,290 pools at collection, each containing samples from two to seven individuals. We detected SARS-CoV-2 in 24 pools, and confirmed the infection in 32 individuals after resampling and testing of 104 samples from positive pools. We completed the testing within 14 days. We would have required 64 days to complete the screening for the same number of individuals if we had based our testing strategy on individual testing. There was no difference in cycle threshold (Ct) values of pooled and individual samples. Thus, compared with individual sample testing, our approach did not compromise PCR sensitivity, but saved 77% of the resources. The present strategy might be applicable in settings, where there are shortages of reagents and the disease prevalence is low, but the demand for testing is high.

A cluster of severe acute respiratory syndrome coronavirus 2 infections in Danang, Vietnam, began July 25, 2020, and resulted in 551 confirmed cases and 35 deaths as of February 2021. We analyzed 26 sequences from this cluster and identified a novel shared mutation in nonstructural protein 9, suggesting a single introduction into Vietnam.

We present a sample pooling approach and the results of its application for mass screening of SARS-CoV-2 in >96,000 asymptomatic individuals. Our approach did not compromise the sensitivity of PCR, while increasing the throughput and reducing 77% of the costs. 22/32 asymptomatic cases would have been missed without mass screening.

We analyzed 1,303 SARS-CoV-2 whole-genome sequences from Vietnam, and found the Alpha and Delta variants were responsible for a large nationwide outbreak of COVID-19 in 2021. The Delta variant was confined to the AY.57 lineage and caused >1.7 million infections and >32,000 deaths. Viral transmission was strongly affected by nonpharmaceutical interventions.

In 2021, Vietnam experienced a large nationwide outbreak of COVID-19, with over 1.7 million infections and 32,000 deaths. We generated 1,303 SARS-CoV-2 whole-genome sequences, and mapped out the public health measures alongside the evolutionary trajectory of the pathogen. The Alpha variant caused sporadic outbreaks in early 2021 prior to the upsurge in cases associated with the Delta variant from June onward. The Delta variant outbreak was almost entirely confined to the AY.57 lineage, accounting for 99.2% of 1,212 Delta variant sequences, and resulting from a single introduction. Viral dispersal from the north, where it was first introduced into Vietnam, to the south, marked the start of the nationwide outbreak, with the south subsequently seeding the virus back to the other regions. Distinct AY.57 phylogenetic clusters in different regions of Vietnam were documented, pointing to the impact of in-country lockdown. Genomic surveillance is critical to inform pandemic response.

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