Transmission interval estimates suggest pre-symptomatic spread of COVID-19

A new study determines the incubation period and serial interval distribution for transmission clusters in Singapore and in Tianjin.

Authors infer the basic reproduction number and identify the extent of pre-symptomatic transmission by collecting outbreak information from Singapore and Tianjin, China, reported from Jan 19 – Feb 26 and Jan 21 – Feb 27, respectively. Then, they estimated incubation periods and serial intervals in both populations.

The results they obtained were: the mean incubation period was 7.1 days for Singapore and 9 days for Tianjin; both datasets had shorter incubation periods for earlier-occurring cases; and the mean serial interval was 4.56 days for Singapore and 4.22 for Tianjin. Besides, authors pointed to early in the outbreaks, infection was transmitted on average 2.55 and 2.89 days before symptom onset (Singapore, Tianjin). Moreover, the estimated basic reproduction number for Singapore was 1.97 secondary cases per infective; for Tianjin it was 1.87 secondary cases per infective.

In conclusion, estimated serial intervals are shorter than incubation periods in both Singapore and Tianjin, suggesting that pre-symptomatic transmission is occurring. Shorter serial intervals lead to lower estimates of Odds Ratio (OR), which suggest that half of all secondary infections should be prevented to control spread.

Link to the paper: https://doi.org/10.1101/2020.03.03.20029983

Editorial Disclaimer: information published during the 2020 COVID-19 pandemic may be updated frequently to reflect the dynamic nature of current understanding.

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