Asymptomatic transmission during the COVID-19 pandemic and implications for public health strategies

Hanalise V. Huff, MD, MPH; Avantika Singh, MD Boston Children’s Hospital, Harvard Medical School, Boston, MA, USA

SARS-CoV-2 spread rapidly within months despite global public health strategies to curb transmission by testing symptomatic patients and encouraging social distancing. There is rapidly emerging evidence highlighting transmission by asymptomatic and pre-symptomatic individuals. Viral load of asymptomatic carriers is comparable to symptomatic patients, viral shedding is highest before symptom onset suggesting high transmissibility before symptoms. Within universally tested subgroups, surprisingly high percentages of COVID-19 positive asymptomatic individuals were found. Asymptomatic transmission was reported in several clusters. A Wuhan study showed an alarming rate of intrahospital transmission, and several countries reported higher prevalence among healthcare workers than the general population. This raises concern that health workers could act as silent disease vectors. Therefore, current public health strategies relying solely on ‘symptom onset’ for infection identification need urgent reassessment. Extensive universal testing irrespective of symptoms may be considered with priority placed on groups with high frequency exposure to positive patients.