Centre for Evidence Based Medicine
Transmission Dynamics of COVID-19

Analysis of the evidence of transmission dynamics of COVID-19
Protocol for a scoping evidence review
Jefferson T, Plüddemann A; Spencer EA; Roberts N; Heneghan C.
Affiliation
Nuffield Department of Primary Care Health Sciences
University of Oxford
Radcliffe Observatory Quarter
OxfordOX2 6GG
Keywords
COVID-19; mode of transmission.

Introduction
In the midst of the COVID-19 pandemic, uncertainty on the characteristics of a novel disease reigns. One ofthe most important aspects of these uncertainties regard the mode and circumstances of transmission of this
newly identified agent.
The table shows the incremental acceleration of SARS CoV-2 cases, hospitalisations and deaths between
the 20th of February and the 10th of March 2020 in Lombardy, mainly the provinces of Lodi and Bergamo.
These were thought to be the first cases of SARS-CoV 2 in Europe.

The explosive nature of the transmission, initially shown by the number of new cases and later byadmissions and deaths, remains unexplained. The age distribution and the speed of transmission does not fitwith what is known of “seasonal” coronaviridae (HCoV-OC43, -229E, -NL63 and -HKU1)​ [1]Centre for Evidence Based Medicine
Transmission Dynamics of COVID-19

Such uncertainties prevent a rational response to the threat and promote extreme actions such as total
lockdown of whole countries. This is an economically unsustainable strategy.
One of the principal uncertainties regards the means by which COVID-19 is transmitted, with special regard
to the factors which may accelerate or delay its spread, the mode of transmission, the role of asymptomatic
infected people, its speed, the possible interactions with wildlife or livestock, urban or rural environments andpopulation density.
Given its novelty, early reliance on models of spread is based on what is known of the dynamics of otherrespiratory infections especially influenza. We now know these are inapplicable to COVID-19.
The first part of the project will consist of a search of the evidence and description with tabulation of thefindings. Again, given the novelty, dynamic theories are likely to be the most frequent studies.
In the second phase, as more information becomes available, it may be possible to either define a mode oftransmission or to set out a series of hypotheses to be tested by further work.
Because of the public health importance of this work and its evolving nature, we will publish this protocol online and post extractions and summaries of included studies with brief comments. Our searches will be
updated once a month and the results posted.
Objectives
Methods
An initial search was undertaken using LitCovid, medRxiv and Google Scholar for the search 'Covid-19and transmission dynamics' with results returned by relevance. Results reviewing was stopped when no new
positive results were returned in 40 hits. Articles were then title screened for inclusion and exclusion. Whenambiguous results were identified, we read the abstract.
Early key transmission dynamic articles, identified in the initial search, were then used to explore forward
citations i.e. which newer papers have cited these key papers​.​ Searches will be updated each month
We divided the studies into two broad categories: 1) observational ecological studies and 2) modellingstudies.
1. Observational studies where the likely mode of transmission and the ecological variables influencing
the mode of viral transmission were studied with special focus on cases and deaths reported as
COVID related deaths. We preliminarily defined these as:
Mode of transmission:
1.1 Droplet borne
1.2 Contact borne
1.3 Pollutant borne
1.4 Oro-fecal
In our preliminary searches we could find no evidence on vector activity so we decided to put this on hold fornow.
We further defined the following variables which may influence transmission:● Settings - defined as in the review by Leclerc et al.​ [2]● Density● Meteorological variables● Latitude and other geographical variables including sunlight
We will not restrict inclusion by study design, but we will include only studies using descriptive and ecologicalmethods to identify the variables and test their relationship with each other and with incidence of cases andCentre for Evidence Based Medicine
Transmission Dynamics of COVID-19

deaths. For background and informative reasons, we will include studies reporting on non-COVID-19
coronaviridae.
2. We will only include modelling studies where the original data relates to transmission outcomes andnot to modelled outcomes. We will hand search the references of these studies.
We will exclude studies of transmission dynamics of non coronaviridae. For each study we will extract
publication data and the variables listed in the extraction sheet and produce both a set of notes for internal
use and a plain language summary for public consumption. We will summarize the methods, the findings andthe main limitations. We will report any assumptions and simplifications made during the data extraction
process.
We will base our evaluation of quality on five criteria: (1) a clearly defined setting; (2) demographic
characteristics described and testing procedures; 3) follow-up length sufficient for the outcomes (4) thetransmission outcomes assessment was defined, and (5) main biases that are threats to the validity. We
piloted the extraction and piloting criteria before finalising them.
We will summarise data narratively by mode of transmission or by defined variables which may influencetransmission and report the outcomes as stated in the paper. Where feasible we will summarise the range ofoutcomes. We will provide a table of research implications (from each paper we will extract the information
on research priorities); and where relevant, we will report implications for policy and practice.
Continual data releaseTo support transparency, rapid flow of information through the scientific community, and scientific debate, we
aim to publish on the CEBM website (cebm.net),​[2] ​summary descriptions of important relevant research
papers identified during this review. Where we consider there are important policy implications we willsummarise these as we progress the review. This process will be ongoing during the data acquisition andwrite-up of the review. We will report the scoping review according to the PRISMA statement on reporting
scoping reviews. [3]​​ We will index the review findings on the ​Oxford Research Archive​.
Funding
This work is supported by the National Institute of Health Research Evidence Synthesis Working group, andby Maria and David Willetts.
References
1. Killerby ME, Biggs HM, Haynes A, et al. Human coronavirus circulation in the United States
2014–2017. ​Journal of Clinical Virology​ 2018;101:52-56. doi:
https://doi.org/10.1016/j.jcv.2018.01.019
2. Leclerc Q, Fuller N, Knight L, et al. What settings have been linked to SARS-CoV-2 transmission
clusters? [version 1; peer review: 1 approved with reservations]. ​Wellcome Open Research
2020;5(83) doi: 10.12688/wellcomeopenres.15889.1cebm.net (website)
3. The Centre for Evidence Based Medicine. Accessed 18 May 2020.
4. Tricco, AC, Lillie, E, Zarin, W, O'Brien, KK, Colquhoun, H, Levac, D, Moher, D, Peters, MD, Horsley,T, Weeks, L, Hempel, S et al. PRISMA extension for scoping reviews (PRISMA-ScR): checklist andexplanation. Ann Intern Med. 2018,169(7):467-473. doi:10.7326/M18-0850

Centre for Evidence Based Medicine
Transmission Dynamics of COVID-19

Annex a – Data extraction sheetTable​. ​Definitions used for each of our transmission setting types (after Leclerc​2​)
Bar
Indoor space such as a bar, club, pub, small live music venues etc.
Building site
Indoor or outdoor space where construction work takes place.
Conference
Indoor professional event with many people interacting and meeting, shaking hands, eating together, team
activities, etc.
Elderly Care
Care homes for the elderly; includes staff and residents. Transmission can occur between staff and residents
but also from visitors.
FuneralIndoor or outdoor burial ceremony; includes close contact with others such as hugging, shaking hands, eating
together, singing, praying, etc
Hospital
Any transmission that occurs within a hospital between patients and/or staff, in a COVID19 ward or not.
Hotel
Any transmission that occurs within the hotel e.g. hotel rooms, shared spaces, reception desk, etc
HouseholdTransmission between individuals in a shared living space
Meal
When people eat together. Meals included took place in restaurants, hotels, cafes, home, etc. Transmission
occurs over a meal by speaking, sharing foods, touching the same surfaces, etc.
PublicWhere transmission occurs on public property and does not fall into any of the other settings e.g. park, welfare
centre, foodbank, etc
Religious
Transmission occurs at a religious event such as mass, services, prayer time, choir practice, etc.
SchoolChildcare or learning environments (schools, nurseries, kindergartens etc). Includes staff and children
Ship
Any ship at sea. Includes crew and/or passengers on board
Shipyard
Large indoor or outdoor space where ships are made or repaired. Includes those working on the ship as wellas customers
Shopping
A shop or shopping centre. Includes customers and those working in the shop.
Sport
Participation in a sporting activity indoor or outdoor e.g. gym or running.
Work
In the workplace, typically an office.
Worker dormitories
A shared living space for workers.