The basic reproduction number of SARS-CoV-2: a scoping review of available evidence

Abstract

Background: The transmissibility of SARS-CoV-2 determines both the ability of the virus to invade a population and the strength of intervention that would be required to contain or eliminate the spread of infection. The basic reproduction number, R0, provides a quantitative measure of the transmission potential of a pathogen. Objective: Conduct a scoping review of the available literature providing estimates of R0 for SARS-CoV-2, provide an overview of the drivers of variation in R0 estimates and the considerations taken in the calculation of the parameter. Design: Scoping review of available literature between the 01 December 2019 and 07 May 2020. Data sources: Both peer-reviewed and pre-print articles were searched for on PubMed, Google Scholar, MedRxiv and BioRxiv. Selection criteria: Studies were selected for review if (i) the estimation of R0 represented either the initial stages of the outbreak or the initial stages of the outbreak prior to the onset of widespread population restriction (lockdown), (ii) the exact dates of the study period were provided and (iii) the study provided primary estimates of R0. Results: A total of 20 R0 estimates were extracted from 15 studies. There was substantial variation in the estimates reported. Estimates derived from mathematical models fell within a wider range of 1.94-6.94 than statistical models which fell between the range of 2.2 to 4.4. Several studies made assumptions about the length of the infectious period which ranged from 5.8-20 days and the serial interval which ranged from 4.41-14 days. For a given set of parameters a longer duration of infectiousness or a longer serial interval equates to a higher R0. Several studies took measures to minimise bias in early case reporting, to account for the potential occurrence of super-spreading events, and to account for early sub-exponential epidemic growth. Conclusions: The variation in reported estimates of R0 reflects the complex nature of the parameter itself, including the context (i.e. social/spatial structure), the methodology used to estimate the parameter, and model assumptions. R0 is a fundamental parameter in the study of infectious disease dynamics however it provides limited practical applicability outside of the context in which it was estimated, and should be calculated and interpreted with this in mind.

The challenges of containing SARS-CoV-2 via test-trace-and-isolate

“…7c). This combination shows stability even for spreads close to the basic reproduction number R H t ¼ R 0 % 3:3 21,26,27 , when implemented extremely efficiently (e.g., with λ s = 0.66 and η = 0.66). However, this…”

“…indicates that compensating the basic reproduction number R H t ¼ R 0 % 3:3 21,26,27 might be very costly, and hence some degree of physical distancing might be required.…”

Numbers of close contacts of individuals infected with SARS-CoV-2 and their association with government intervention strategies

“…In addition, interventions such as restriction of travel or limiting social gatherings may be introduced which are designed to limit the number of contacts of an individual, contributing to a reduction in the overall force of infection for the population. Ultimately, the effectiveness of the overall set of interventions might be determined by indicators of the rate of new infections in the population such as incidence rates (eg 14-day cumulative number of COVID-19 cases per 100,000 [6]) or time-varying reproduction numbers [7]. However, these indicators are by their nature somewhat retrospective and indirect.…”

“…Finally, the time-varying reproduction number (Rt) is a key metric describing the effectiveness of viral transmission in the population [7]. Current estimates of Rt are primarily inferred from epidemiologic models which involve compartmentalisation of individuals according to their infection and disease status, allowing the number of individuals in the population within the susceptible, exposed, infectious, and recovered (SEIR) compartments to be described at a point in time [10].…”

Science’s Response to COVID-19

“…12 CoVID-19's mortality is significantly less than MERS-CoV and SARS-CoV; nonetheless, the mortality of CoVID-19 is significantly higher than common flu, and at the low end of estimates of the mortality of the Spanish flu of 1918, which killed ~50 million people worldwide 13 (equivalent to quadruple that number in today's figures). 14 SARS-CoV-2 shows a reproductivity (R) number ~3, 15 although estimates vary considerably 16 and interpretation of R needs careful consideration. Indeed, R values vary as a function of method and circumstances: 17 e.g., some methods show that the R value of CoVID-19 aboard the Diamond Princess cruise ship was ~15.…”