This preprint reports robust induction of SARS-CoV-2-specific neutralizing antibodies in 94% of 175 patients with clinically mild COVID-19 within 2 weeks of symptom onset. Compared with young patients, middle-aged and older patients in this cohort had higher titres of neutralizing and binding antibodies. As older patients are generally considered at greater risk of severe disease, the robust humoral responses in this cohort may explain their apparent protection. Of note, 10 of 175 patients recovered without developing detectable neutralizing antibody titres, suggesting that antiviral binding antibodies and cellular immune responses can both result in convalescence. Longitudinal observations in addition to stringent clinical and immunological characterization are needed to further assess the specificity and relative contribution to protection of neutralizing antibodies against SARS-CoV-2.