Temporal dynamics in viral shedding and transmissibility of COVID-19

Temporal dynamics in viral shedding and transmissibility of COVID-19. Spencer EA, Heneghan C.


Published on July 23, 2020

Reference He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19.  Nat Med. 2020;26(5):672-675. 2020
Study type
Country China
Setting Hospital
Funding Details The Department of Science and Technology of Guangdong Province and a commissioned grant from the Health and Medical Research Fund from the Government of the Hong Kong Special Administrative Region.
Transmission mode Presymptomatic
Exposures Hospital

Bottom Line

Among 77 transmission pairs, highest viral load in throat swabs was observed at the time of symptom onset and declined thereafter; therefore infectiousness may peak prior to symptom detection.

Evidence Summary

Among 94 patients with non severe laboratory-confirmed COVID-19 admitted to Hospital, 414 throat swabs were collected from symptom onset up to 32 days after onset. 

We detected high viral loads soon after symptom onset, which then gradually decreased towards the detection limit at about day 21. There was no obvious difference in viral loads across sex, age groups and disease severity

Considered together these data suggested that 44% (95% CI, 25 to 69%) of secondary cases were infected during the index cases’ presymptomatic stage.

What did they do?

Temporal patterns of viral shedding in 94 patients with laboratory-confirmed COVID-19 admitted to Guangzhou Eighth People’s Hospital, were investigated by taking repeated throat swabs and testing for viral presence and viral load up to 32 days after symptom onset.

Study reliability

This study relied on retrospective reporting of onset of symptoms, which may be biased by subsequent diagnoses.  The authors note that viral shedding in this study may have been influenced by treatment for COVID-19 and the natural history may differ in another context.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Yes Yes Yes Unclear

What else should I consider?

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.