A systematic review of SARS-CoV-2 transmission
A systematic review of SARS-CoV-2 transmission. Jefferson T, Heneghan C.
Published on June 22, 2020
Transmission Dynamics of COVID-19
||Koh WC, Naing L, Rosledzana MA, Alikhan MF, Chaw L, Griffith M, et al. What do we know about SARS-CoV-2 transmission? A systematic review and meta-analysis of the secondary attack rate, serial interval, and asymptomatic infection. medRxiv. 2020 2020
||Household and non-household
||Person to person, Close Contact
The mean household SAR was 15% (95% CI: 12% to 19%) – ranging from 6.6% in Taiwan to more than 30% in four Chinese cities. Secondary attack rate from symptomatic index cases contact was greater than asymptomatics.
The secondary attack rate (SAR) is defined as the probability that an exposed susceptible person develops disease caused by an infected person.The mean household SAR is 15% (95% CI: 12% to 19%) – ranging from 6.6% in Taiwan to more than 30% in four Chinese cities including Wuhan
The mean non-household rate was 4.0% (95% CI: 2.8% to 5.2%) with wide variation across the settings: 73% in a chalet, 53% in a choir, 18% dining with a case and 15% in a church event.
Secondary attack rates from symptomatic index cases contacts were 2.5 times greater than those of asymptomatic.
The serial interval was defined as the time between disease symptom onset of a case and that of its infection. Asymptomatic cases were defined as those with laboratory confirmation but without clinical signs and symptoms at diagnosis (including pre-symptomatic).
The mean asymptomatic proportion at diagnosis was 26% (95% CI: 19%, 33%), decreasing with age (42%) in children.
What did they do?
The authors performed a search for studies in PubMed and pre-print articles in medRxiv and bioRxiv between 1st of January and 15th of May 2020 with slightly different inclusion criteria according to the fixed variable of interest: secondary attack rate (20 studies) across different settings; clinical onset serial interval (18 studies), and the proportion of asymptomatic infection (66 studies). They only included studies reporting original data, thus excluding models. Although they pooled data they did not carry out a methodological quality assessment.
There is considerable heterogeneity amongst the studies that undermine the pooled estimates.
|Clearly defined setting
||Demographic characteristics described
||Follow-up length was sufficient
||Transmission outcomes assessed
||Main biases are taken into consideration
What else should I consider?
This evidence from this review needs updating and increasing. Although a wide variety of settings were included in the analysis, ultimately each setting cell had several small studies which introduced heterogeneity perhaps because of the way they had been carried out in the midst of a pandemic. We were unable to identify a protocol for the review. In the absence of a predefined protocol, studies are subject to significant uncertainties due to changes in the analysis that may not be clear.
About the authors
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
Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.
Tom Jefferson, epidemiologist.