Background: Vietnam confirmed its first case of SARS-CoV-2 infection on January 23, 2020 among travelers from Wuhan, China and experienced several clusters of community transmission until September. Vietnam implemented an aggressive testing, isolation, contact tracing, and quarantine strategy in response to all laboratory-confirmed cases. We report the results of SARS-CoV-2 testing during the first half of 2020 in northern Vietnam. Methods: From January through May, 2020, 15,650 upper respiratory specimens were collected from 14,470 suspected cases and contacts in northern Vietnam. All were tested for SARS-CoV-2 by real-time RT-PCR. Individuals with positive specimens were tested every 3 days until negative twice. Positive specimens from 81 individuals were cultured. Results: Among 14,470 tested individuals, 158 (1.1%) cases of SARS-CoV-2 infection were confirmed; 89 were imported and 69 were associated with community transmission. Most patients (122, 77%) became negative after two tests, with 11 and 4 still testing positive when sampled a fourth and fifth time, respectively. Among 81 specimens with Ct values <30, SARS-CoV-2 was isolated from 29 (36%). Seven patients testing positive again after testing negative had Ct values >30 and negative culture. Conclusion: Early and widespread testing for SARS-CoV-2 in northern Vietnam identified very few cases which, when combined with other aggressive strategies, may have dramatically contained the epidemic. We observed rapid viral clearance and very few positive results following clearance. Large scale molecular diagnostic testing is a critical part of early detection and containment of COVID-19 in Vietnam and will remain necessary until a vaccine is widely implemented.