Table 1. Background characteristics of the 29 studies included in the meta-analysis.

Serial number	Author, Study’s location	Model used to estimate the reproductive number	Time/period for which the reproductive number was estimated	Assumption(s) that was/were considered to estimate the reproductive number	Method used to estimate the reproductive number	Reproductive number (95% CI)	Study-quality assessment (earned score in the scale of 9)++
1	Read et al, 2020 [40], China and overseas	Susceptible-Exposed-Infected-Removed (SEIR) model	1st Jan 2020 to 22nd Jan 2020	Cases daily time increase follows a Poisson distribution	MLE1	3.11 (2.39–4.13)	7
2	Zhang et al., 2020 [31], Diamond Princess Cruise ship, Japan	Epidemic model incorporated by the data	16th Feb 2020	The mean serial interval (SI)2 7.5 days, standard deviation (SD) 3.4 days	MLE	2.28 (2.06–2.52)	7
3	Liu et al., 2020 [39], China and overseas	No model mentioned	before 23rd Jan 2020	With generation time (GT)3 of 8.4 days	EGR	2.90 (2.32–2.52)	8
					MLE	2.92 (2.28–3.67)
4	Majumder & Mandl, 2020 [24], Wuhan, China	Susceptible-Infected-Recovered/Removed (SIR) model	Dec 8, 2019, to Jan 26, 2020	Mean SI 8 (range 6–10) days	SEIR method	2.55 (2.00–3.10)	6
5	Riou & Althaus, 2020 [7], China and overseas	No model mentioned	before 18th Jan 2020	The mean GT varied 7–14 days	Stochastic simulation	2.2 (1.4–3.8)	8
6	Tang et al., 2020 [18], China	SEIR model (with isolation, quarantined)	31 Dec 2019 to 15th Jan 2020	The incubation period is 7 days	NGMA1	6.47 (5.71–7.23)	9
7	Zhao, Lin et al., 2020 [19], China	Epidemic curve by time-series data	10th Jan to 24th Jan 2020	8-fold reporting rate	EGR	2.24 (1.96–2.55)	7
				2-fold reporting rate		3.58 (2.89–4.39)
				0-fold reporting rate		5.71 (4.24–7.54)
8	Zhao, Musa, et al., 2020 [20], China	Epidemic curve using time series information	1st Jan to 15th Jan 2020	Constant screening effort applied in the Wuhan at the same point in time.	EGR	2.56 (2.49–2.63)	8
9	Shen et al., 2020 [25], Hubei province, China	SEIR model	12th Dec 2019 to 22nd Jan 2020	5–6 days of incubation	SEIR method1	4.71 (4.50–4.92)	8
				With intervention and 5–6 days of the incubation period	SEIR method	2.08 (1.99–2.18)
10	Q. Li et al., 2020 [23], Wuhan, China	Epidemiologic time delay distribution	Before 22nd Jan 2020	Mean SI 8.4 days and SD 3.8 days	Fitted transmission model with zoonotic infection	2.20 (1.40–3.90)	8
11	J. T. Wu et al., 2020 [27], Wuhan, China	SEIR model	31 Dec 2019 to 28th Jan 2020	Mean SI of 8.4 days	MCMC1	2.68 (2.47–2.86)	9
12	Imai et al., 2020 [15], China	No model mentioned	before 18th Jan 2020	High level of variability & generation time is 8.4 days	Computational modelling epidemiologic trajectories	2.60 (1.50–3.50)	7
13	Kucharski et al., 2020 [38], Wuhan and international travellers	SEIR model	29th Dec 2019 to 23rd Feb 2020	Mean incubation period is assumed to be 5.2 days & SD 3.7 days	MLE	2.35 (1.15–4.77)	9
				Intervention with mean incubation period 5.2 days & SD 3.7 days	MLE	1.05 (0.41–2.39)
14	Ki, 2020 [33], South Korea	Epidemic curve fitting	20 Jan to 10 Feb 2020	Not Available (NA)	EGR	0.48 (0.25–0.84)	9
15	Choi & Ki, 2020 [32], South Korea	SEIR model	20 Jan to 17 Feb, 2020	Overseas infections are separated	SEIR method	0.56 (0.51–0.60)	9
16	Shim et al., 2020 [34], South Korea	Epidemic curve fitting with the growth model	20th Jan to 26th Feb 2020	With mean GT 4.41 days and SD 3.17 days	Simulation	1.50 (1.40–1.60)	8
17	Lai et al., 2020 [41], Genetic data from GISAID	Phylogenetic estimation	4th Feb 2020	Based on the exponential growth rate of 0.218 per days	EGR	2.60 (2.10–5.10)	9
				The evolutionary rate set to the value of 8.0 × 10–4 subs/site/year	Birth-death skyline estimate	1.85 (1.37–2.40)
18	Jung et al., 2020 [42], Outside of China	No model mentioned	before 24 Jan 2020	Mean SI 7.5 days and SD 3.4 days	EGR	3.19 (2.66–3.69)	8
19	Song et al., 2020 [17], China	SEIR model	15 to 31 Jan 2020	Using generation intervals	EGR	3.74 (3.63–3.87)	6
				Using generation intervals	MLE	3.16 (2.90–3.43)
				The model fitted best 27th Jan	SEIR method	3.91 (3.71–4.11)
20	Sanche et al., 2020 [16], China	SEIR model	15 to 30 Jan 2020	with 7–8 days of the SI	EGR	5.80 (4.40–7.70)	7
				with 6–9 days of the SI		5.7 (3.80–8.90)
21	Mizumoto & Chowell, 2020 [29], Diamond Princes Cruise ship, Japan	No model mentioned	20 Jan to 18 Feb, 2020	Mean SI 7.5 days and SD 3.4	NGMA	5.8 (0.6–11.0)	9
22	Kuniya, 2020 [28], Japan	SEIR model	15 Jan to 29 Feb 2020	Infected increases at a rate of daily time increment	NGMA	2.60 (2.40–2.80)	6
23	Iwata & Miyakoshi, 2020 [43], Outside of China	SEIR model	Not Available (NA)	One infected entered a community of 1000 population.	MCMC	6.5 (5.6–7.2)	7
24	Wan et al., 2020 [26], Wuhan, China	SEIR model	22 Jan to 07 Feb 2020	7 days incubation period and 14 days of the infectious period	SEIR method	1.44 (1.40–1.47)	8
25	Yuan et al., 2020 [36], Italy	No model mentioned	23 Feb to 9 Mar 2020	Mean GT 5.6 days and SD 2.6 days	EGR	3.27 (3.17–3.38)	9
	Yuan et al.,2020 [36], France					6.32 (5.72–6.99)
	Yuan et al.,2020 [36], Germany					6.07 (5.51–6.69)
	Yuan et al.,2020 [36], Spain					5.08 (4.51–5.74)
26	Chintalapudi et al., 2020 [44], Italy	No model	26 Feb to 20 Apr 2020	Using estimated SI with non-pharmaceutical (NP) interventions	MLE	1.85 (0.60–2.30)	8
27	Hyafil and Morina, 2020 [37], Spain	SIR model	Upto 13 Mar 2020	Based on the hospitalized data with 7.65 days incubation period	SEIR method	5.89 (5.86–7.09)	8
	Hyafil and Morina, 2020 [37], Spain	SIR model	Upto 13 Mar 2020	Based on the detected cases with 10.2 days incubation period	SEIR method	6.91 (6.95–7.39)
	Hyafil and Morina, 2020 [37], Spain	SIR model	16 Mar to 15 Apr 2020	Based on the hospitalized data with 7.65 days incubation period with initial interventions	SEIR method	1.86 (1.10–2.63)
	Hyafil and Morina, 2020 [37], Spain	SIR model	16 Mar to 15 Apr 2020	Based on the detected cases with 10.2 days incubation period with initial interventions	SEIR method	2.22 (1.92–2.74)
	Hyafil and Morina, 2020 [37], Spain	SIR model	31 Mar to 12 Apr 2020	Based on the hospitalized data with 7.65 days incubation period with interventions for full restrictions	SEIR method	0.48 (0.15–1.17)
	Hyafil and Morina, 2020 [37], Spain	SIR model	31 Mar to 12 Apr 2020	Based on the detected cases with 10.2 days incubation period with interventions for full restrictions	SEIR method	0.85 (0.50–1.05)
28	Zhang et al., 2020 [45], Wuhan, China	SEIQ model	21 Jan to 20 Feb 2020	Mean SI 5.2 days and hospital quarantine 12.5 days	MCMC	5.50 (5.20–5.80)	7
29	Shao et al., 2020 [46], China	Fiduan-CCDC model	Not specified	Mean SI 7.5 days with SD 3.4 days	SEIR method	3.32 (3.25–3.40)	7

Note: All studies included in the meta-analysis were summarized in this table. Studies included in the narrative synthesis were summarized in Table 3. ¹EGR: Exponential growth rate method; MLE: Maximum Likelihood Method; MCMC: Markov Chain Monte Carlo Method; NGMA: Next-Generation Matrix Approach and SEIR method = β/γ method. R: Reproductive number, 95% CI, 95% Confidence Interval.

²Serial interval refers to the duration of time between the onset of symptoms in an index case and a secondary case.

³Generation time refers to the time interval between successive infections in the chain of transmission.

⁺⁺Study quality was assessed through the National Institutes of Health (NIH) study quality assessment. Details results are presented in S4 Table in S1 File.