Unequal effects of SARS-CoV-2 infections: model of SARS-CoV-2 dynamics in Cameroon (Sub-Saharan Africa) versus New York State (United States)

Figures & data

Figure 1. Framework of COVID-19 model.

Table 1. Variables of the model.

Variables	Descriptions	Variables	Descriptions
S	susceptible	E	exposed
$I_y$	young infected/infectious (<50yrs)	$I_s$	senior infected/infectious (≥50yrs)
$I_m$	self-medicated infected/infectious	H	hospitalized (serious cases)
Q	isolated (on treatment)	R	removed/recovered
V	vaccinated	C	Corona virus

Note: All variables are in units of population, except C whose unit is number of virions.

Table 2. Baseline values for the model parameters.

Parameter	Definition	Estimated values	Sources
τ	proportion of pop. with pre-acquired immunity	0 (NYS), 80% (Cmr)	fitted
β	contact rate with the virus	0.41 (NYS), 0.182 (Cmr) d${}^{-1}$	fitted
γ	transition rate $E\to I_i$	0.19 d${}^{-1}$	estimated
θ	fraction of youth who become infectious	0.029 (NYS), 0.323 (Cmr)	fitted
${\theta }_{ym}$	fraction of $I_y$ who self-medicate	0.081 (NYS), 0.124 (Cmr)	fitted
${\theta }_{sm}$	fraction of $I_s$ who self-medicate	0.0025 (NYS), 0.328 (Cmr)	fitted
${\alpha }_y$	detection rate of $I_y$	0.5 d${}^{-1}$	estimated
${\alpha }_s$	detection rate of $I_s$	1 d${}^{-1}$	estimated
${\mu }_m$	removal rate of $I_m$	$5.36\times {10}^{-2}$ d${}^{-1}$	estimated
${\mu }_s$	removal rate of $I_s$	$3.57\times {10}^{-2}$ d${}^{-1}$	estimated
${\mu }_y$	removal rate of $I_y$	$7.14\times {10}^{-2}$ d${}^{-1}$	estimated
${\mu }_Q$	removal rate of Q	$7.14\times {10}^{-2}$ d${}^{-1}$	estimated
${\mu }_H$	removal rate of H	$3.57\times {10}^{-2}$ d${}^{-1}$	estimated
${\mu }_C$	dissipation rate of C	5.33 (NYS), 11.18 (Cmr) d${}^{-1}$	estimated
${\lambda }_y$	shedding rate of C by $I_y$	31.6 vir pop${}^{-1}$ d${}^{-1}$	estimated
${\lambda }_s$	shedding rate of C by $I_s$	124.5 vir pop${}^{-1}$ d${}^{-1}$	estimated
${\lambda }_m$	shedding rate of C by $I_m$	78.1 vir pop${}^{-1}$ d${}^{-1}$	estimated
${\delta }_C$	consumption rate of C	0.12 (NYS), 0.0277 (Cmr) pop${}^{-1}$ d${}^{-1}$	fitted
ν	vaccination rate	$1.2\times {10}^{-3}$ (NYS), $1.2\times {10}^{{}^{-5}}$ (Cmr) d${}^{-1}$	estimated
σ	rate of immunity wane	$1.2\times {10}^{-4}$ d${}^{-1}$	fitted
$K_C$	half saturation of C for successful infection	300 vir ${}^{-1}$	estimated
N	total population	$20\times {10}^6$ (NYS), $28\times {10}^6$ (Cmr) pop	estimated

Note: $\text{Cmr}=\text{Cameroon}$, NYS=New York State.

Table

Conditions		Half-life (hours)		Half-life (hours)
$4^{\circ }\text{C}/40\mathrm{\%}$ RH		3.3 (2.6–4.4)		5.8 (4.8–7.3)
${21}^{\circ }\text{C}/40\mathrm{\%}$ RH	Nasal mucus	3.1 (2.5–4.1)	Sputum	3.1 (2.3–4.6)
${27}^{\circ }\text{C}/85\mathrm{\%}$ RH		1.5 (1.2–1.9)		1.5 (1.1–2.4)

Figure 2. COVID-19 in Cameroon and New York State (U.S.A.): Model results vs data. (A) 30-day rolling number of COVID-19 new infection cases in Cameroon between 17 June and 25 September 2021: N=28 million, RE=6.44%, ${\mathcal{R}}_0=1.84$; (B) Daily number of COVID-19 new infection cases in New York State between 17 June and 16 August 2021: N=20 million, RE=4.3%, ${\mathcal{R}}_0=0.13$. The parameter values are in Table 2.

Figure 3. Parameter sensitivity analysis for the severity of COVID-19 in Cameroon (Jun 17-Sep 25, 2021) and New York State (Jun 17-Aug 16, 2021). All the parameters have p-values $<0.01$ except ${\mu }_C$ whose p-value is $>0.1$; we exclude it from the analysis. (a) Cameroon and (b) New York State (U.S.A.).

Figure 4. Values of ${\mathcal{R}}_0(\text{β},\nu ,\tau ;T_{\text{Cmr}})$ in Cameroon and $burden\mathrm{\_}ratio$ relative to New York State. (a) ${\mathcal{R}}_0$ increases with β and decreases with ν and τ. (b) $burden\mathrm{\_}ratio$ decreases exponentially with $burden\mathrm{\_}ratio\simeq 16$ when $\nu =0$, and $burden\mathrm{\_}ratio<1$ when $\nu \ge 80\mathrm{\%}$. The dashed line represents $burden\mathrm{\_}ratio=1$. All other parameters are listed in Table 2. (a) ${\mathcal{R}}_0(\text{β},\nu ,\tau ;T_{\text{Cmr}})$ in Cameroon and (b) $burden\mathrm{\_}ratio$: COVID-19 severity in Cameroon relative to New York State.