Estimate of the Basic Reproduction Number for COVID-19: A Systematic Review and Meta-analysis

Article information

J Prev Med Public Health. 2020;53(3):151-157

Publication date (electronic) : 2020 March 20

doi : https://doi.org/10.3961/jpmph.20.076

Yousef Alimohamadi^1,2, Maryam Taghdir³, Mojtaba Sepandi^,3,4

¹Pars Advanced and Minimally Invasive Medical Manners Research Center, Pars Hospital, Iran University of Medical Sciences, Tehran, Iran

²Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

³Health Research Center, Lifestyle Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran

⁴Department of Epidemiology and Biostatistics, Faculty of Health, Baqiyatallah University of Medical Sciences, Tehran, Iran

Corresponding author: Mojtaba Sepandi, PhD Health Research Center, Lifestyle Institute, Baqiyatallah University of Medical Sciences, Tehran 143591-13189, Iran E-mail: msepandi@gmail.com

Received 2020 March 11; Accepted 2020 March 20.

Abstract

INTRODUCTION

In December 2019, a series of pneumonia cases with no identified cause appeared in Wuhan, Hubei Province, China, with clinical symptoms similar to viral pneumonia [1-3]. Most of the reported cases were in patients who worked or lived around the local Huanan Seafood Wholesale Market, where live animals were also sold [4]. This new virus infecting humans was initially named the 2019 novel coronavirus, and the World Health Organization (WHO) subsequently issued updated nomenclature, in which the virus is referred to as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the disease that it causes is referred to as coronavirus disease 2019 (COVID-19) [5]. Because of its high contagiousness and morbidity, this infection is considered by WHO as a global emergency [6]. As a reflection of the high transmissibility of this viral infection, by January 26, 2020 more than 2000 confirmed cases of COVID-19 had been identified in China, mainly in Wuhan [7]. This number then dramatically increased, with the number of confirmed cases in China reaching 66 580 by February 15, 2020, with 1524 deaths [8]. Human-to-human transmission of COVID-19 was confirmed [9] and cases were reported in countries other than China [10]. Because of the high infectiousness of SARS-CoV-2 among the susceptible population, the calculation of the basic reproduction number (R₀) is essential for implementing prevention measures [1]. R₀ is an epidemiological metric that can be used to assess the contagiousness of infectious agents. This index presents the average number of new cases generated by an infected person [11,12]. Therefore, a high R₀ indicates that an infectious agent is highly contagious. Since the epidemic began in China, numerous papers have been published on this issue. However, because of discrepancies in the results of those studies, the current systematic review and meta-analysis aimed to estimate the pooled R₀ for the COVID-19 outbreak, using original articles published during 2020.

METHODS

RESULTS

We identified 85 studies, of which 23 were duplicates, leaving 62 reports. A total of 55 reports passed the initial screening, and 23 reports passed the full-text assessment for eligibility (Figure 1). The reasons for exclusion were as follows: reporting of effective reproductive number instead of R₀ and insufficient data. Finally, we included 23 studies in this systematic review (Table 1). No studies were excluded due to poor quality. In the current study, 23 studies with 29 records that estimated the R₀ of COVID-19 were entered into the analysis. The studies used a broad range of methods to estimate R₀ for COVID-19. All the studies included in the meta-analysis were conducted in 2020 in China. The mean R₀ reported in the articles was calculated as 3.38±1.40, with a range of 1.90 to 6.49. More information is shown in Table 1.

Figure. 1.

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram for the studies included in the current meta-analysis.

Table 1.

Descriptive characteristics of the studies included in the meta-analysis

Pooled Estimation of Basic Reproduction Number

According to the results of the random-effects model, the pooled R₀ for COVID-19 was estimated as 3.32 (95% CI, 2.81 to 3.82). This means that each person infected with COVID-19 transmitted the infection to between 3 and 4 susceptible people on average (Figure 2, Table 2). There was significant heterogeneity among studies (I²=99.4%, p from the chi-square test for heterogeneity <0.001, and T²=1.72) (Table 2).

Figure. 2.

Forest plot of the estimated basic reproduction number of coronavirus disease 2019. ES, effect size; CI, confidence interval.

Table 2.

Pooled estimation of the basic reproduction number of coronavirus disease 2019

Meta-regression

The meta-regression analysis showed that the type of model used to estimate R₀ did not have a significant effect on heterogeneity among studies (p=0.81). The distribution of the estimated R₀ according to the model used is shown in Figure 3. The numbers on the χ-axis in Figure 3 represent the type of method used to estimate R₀, using the following coding: stochastic Markov chain Monte Carlo method: 1, dynamic compartmental model; 2, statistical exponential growth model; 3, statistical maximum likelihood estimation; 4, mathematical transmission model; 5, mathematical incidence decay and exponential adjustment; 6, stochastic simulation of early outbreak trajectories; 7, mathematical susceptible, exposed, infected, and resistant (SEIR)-type epidemiological model; 8, other mathematical models; 9, networked dynamics metapopulation model; 10, Fudan-Chinese Center for Disease Control and Prevention model; 11, susceptible, exposed, infected and quarantined (SEIQ) model; 12, coalescent-based exponential growth and a birth-death skyline model; 13, coalescent-based exponential growth and a birth-death skyline model; and 14, type of model not mentioned.

Figure. 3.

Distribution of the estimated basic reproduction number according to the model used.

DISCUSSION

It is necessary to estimate the R₀ of COVID-19 to determine the severity and size of the pandemic, as well as to design appropriate interventions and responses to protect the population and to control the spread of the disease [35]. The estimated R₀ value is important in infectious disease epidemiology because the intensity of transmission must be reduced by 1-1/R₀ to eliminate the outbreak. For example, at R₀=2.5, this fraction is 60.0%, but at R₀=3.2, this fraction is 68.7%. Mathematical models play an important role in decision-making during outbreak control [36]. Our systematic review and meta-analysis found that the overall R₀ was 3.32 (95% CI, 2.81 to 3.82), which is higher than the WHO estimates of 1.4 to 2.5 (11) but similar to the results of an earlier review of 12 articles that were conducted in China (11). Our estimation is similar to the R₀ values estimated for the severe acute respiratory syndrome epidemic in Beijing, China (R₀=4.91) [37], and for Middle East respiratory syndrome in Jeddah, Saudi Arabia (R₀=3.5 to 6.7) [38]. Such a high R₀ indicates that the virus can go through at least 3 to 4 generations of transmission [22]. Similar to reviews of R₀ for other pathogens [39-41], it is important to highlight regarding our results that R₀ is not an intrinsic characteristic of a given pathogen, but rather describes the transmissibility of that pathogen within a specific population and setting. The estimated R₀ depends on factors such as social and demographic variables, the estimation method used, the validity of the underlying assumptions, and the biology of the infectious agent. For example, the frequency of contacts may depend on population size and cultural factors, which can vary across regions. In addition, estimates of R₀ may be somewhat error-prone for reasons such as data insufficiency and the short time period analyzed. As more studies are done and more data are produced, the hope is that this error will be reduced. Our results showed significant heterogeneity among studies (I²=99.3%, p from the chi-square test for heterogeneity <0.001, and T²=1.72). One reason for this issue is that it is difficult to calculate the exact number of infected cases during an outbreak. The variation in R₀ values reported by different studies indicates that precisely estimating R₀ is rather difficult. Additionally, R₀ can be affected by environmental factors and modeling methodology [12]. There are many calculation methods for R₀ [42]. Our review was restricted to Chinese articles. For other countries, surveillance data are needed either to calculate R₀ or to extrapolate R₀ estimates from a comparable setting.

It also seems necessary to consider the reasons why high R₀ values were reported in some studies. Modeling assumptions may be a reason for this issue. Usually, high R₀ values are calculated in the early stages of an epidemic, both because of the small sample size and the lack of awareness about the disease, which results in inadequate preventive measures being taken. Since the number and patterns of people’s contacts in different populations vary because of factors including culture and the level of literacy in the community, R₀ values vary among different populations and even among subgroups of a single population. In fact, the total value of R₀ in a population is the average of the R₀ subtypes in that community. It is therefore important to note that even if the total R₀ value in a population is low (even less than 1), the likelihood of transmission in some subgroups of that population may still be high. Given the rapid spread of the disease and the dependency of the effectiveness of control measures on factors such as the frequency of asymptomatic infections and the potential for disease transmission before symptom onset, COVID-19 seems to be relatively difficult to control. As a measure used to quantify the transmissibility of a disease in a population, R₀ is dependent on the population as well as the method of calculation. Our findings suggest that measures such as preventing large gatherings, restricting transportation, and closing schools and universities may be necessary to control this pandemic.

CONCLUSIONS

Considering the estimated R₀ for COVID-19, reducing the number of contacts within the population is a necessary step to control the epidemic. So Implementation of the social distancing program, preventing large gatherings, restricting transportation, and closing schools and universities may be necessary to control this pandemic. The estimated overall R₀ was higher than the WHO estimate.

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