Table 1.

Characteristics of studies (n=15 studies) included in the systematic review

Author	Setting	Population	Design	Sample (n)	COVID-19 Outcome	Exposure	Summary of study findings
Bergman and Fishman18	Africa	Adults	Modelling	446	Infection	Mobility	There was no statistically significant association between transmission rates and lagged mobility. However, there is limited information about Google workplace mobility data and COVID-19 infection as Apple mobility data are limited in Africa unlike other regions.
Clark et al19	Africa/global	General	Modelling	1.7 billion	Severity	Age, sex, comorbidity and continent	Individuals who are diagnosed with at least one underlying condition are at risk of severe COVID-19 disease. Although not different by sex, a total of 1.17 billion (22%) of the global population were estimated to be at risk of sever COVID-19 disease, and the prevalence of one or more comoribid condition was approximately 10% by age 25 years, 33% by 50 years and 66% by 70 years. A total of 400 million (6%) of the global population were estimated to be at risk of sever COVID-19 disease and is higher in older people. The most prevalent conditions in those aged 50+ years were CKD, CVD, CRD and diabetes— the prevalence of multimorbidity (2+ underlying chronic illness) was three times higher in Europe than in Africa (10% vs 3%).
Daon et al20	Africa/global	General	Modelling	1364 major airports (connections)	Infection	City connectivity	An outbreak of COVID-19 in Africa is most likely to originate from a passenger who travelled from Europe, and the average risk of COVID-19 infection originated from airport in Africa is 0.06, lower result compared with airports in Asia with an estimated risk of 0.51. The airport with the highest risk to initiate an outbreak in Africa is in Johannesburg with a risk estimate of 0.1.
Davies et al7	Africa/global	General	Modelling	–	Infection Severity	Age	People younger than 20 years old are roughly half susceptible as those who are older than 20 years old. In addition, 75% of infections are subclinical in children ageing between 10 and19 years as compared with 24% in people aged 70 years and above.
Diop et al21	Africa	General	Modelling	–	Infection Severity	Residence, population density, comorbidity (HIV, TB and anaemia)	The rate of COVID-19 infection increases as the population density increases. Linked to this, the rate of infection is low in rural settings than in urban areas. The study reported that comorbidity would increase severity of the disease. The rate of anaemia, TB and HIV compared with the rate of DM, HTN and obesity is higher in Africa than other continents, and these (anaemia, TB and HIV) are the underlying conditions that lead to COVID-19 related severity in Africa.
Gayawan et al22	Africa	General	Spatio-temporal analysis	Not specified	Infection	Number of physicians. Number of hospital beds.	Positive correlation was revealed between COVID-19 and number of physicians (r=0.49, p value=<0.001) and hospital beds (r=0.14, p value=0.34) though only the estimate for physicians is significant. The spatio-temporal analysis reveals that the occurrence and burden of COVID-19 in Africa varied geographically with neighbouring countries particularly in the western part of the continent, which could imply that neighbouring countries pose significant importation risk to each other.
Hossain et al23	Africa/global	General	Modelling	1 174 652	Infection	Weather, economic openness and political democracy	Countries with warmer temperatures showed slower spread than their comparator. Countries with higher economic openness had higher infection rates than with lower economic openness. The countries with stronger political democracy had higher infection rates than with weaker political democracy.
Jaffe and Vera24	Africa/global	General	Cross- sectional	Dataset of 36 countries	Infection Mortality	Imports of goods and services, international tourism, electric power consumption and population over 65 years old	Countries that were connected to the global economy tended to have a higher risk of infection, while the risk of mortality from the disease are higher in less globalised low-income countries. Countries with higher imports of goods and services and international tourism had higher infection rates than their comparator.
Kubota et al25	Africa/global	General	Modelling study	1055 countries	Infection	Age, precipitation, temperature, international travel, BCG vaccination and malaria infection	A negative correlation between the accumulated numbers of the COVID-19 cases and the following variables: mean temperature, BCG vaccination effect and malaria infection. The study found a positive correlation between the accumulated numbers of the COVID-19 cases and the following variables: mean precipitation, the relative frequency of foreign visitors per population, GDP per person, population density and relative proportion of people ≥65 years old.
Maitra et al 26	Africa/global	General	Cross-sectional	422 582	Mortality	Health expenditure	Countries with low health expenditure (percentage of GDP) were significantly associated with higher case fatality rate (p=0.0017).
Maraghi et al27	Africa/global	Not specified	Cross-sectional	>1000 but globally	Case fatality and recovery rate	Prevention, detection, response, risk environment indices and global health security (GHS)	Prevention (r=−0.988, −0.1.0 to −0.548), p=0.012), detection (r=−0.979 (−1.000 to –0.312), p=0.021), response (r=−0.965 (−0.999 to −0.051), p=0.035) and GHS (r=−0.995 (−1.000 to −0.786), p=0.005) were negatively correlated with case fatality rate in African countries.
Muneer et al28	Africa/global	General	Web-based survey (worldometer)	–	Infection	Malaria prevalence	Ahigh rate of malaria was negatively correlated with COVID-19 (r=−0.15, p=0.02).
Okpokoro et al8	Africa/global	General	Ecologic study		Mortality	COPD and tobacco use	Mortality was positively correlated with COPD (rho=−0.28, p=0.09) and tobacco use (rho=−0.01, p=0.91) although not statistically significant. Similarly, the study showed that mortality was negatively correlated with life expectancy (rho=−0.09, p=0.24), quality of air (rho=−0.02, p=0.84) and life expectancy (rho=−0.24, p=0.1).
Onovo et al9	Sub-Saharan Africa (SSA)	General	Survey	–	Infection	Adult HIV incidence rate, infant’s pneumococcal conjugate-based vaccine, incidence of malaria and diarrhoea treatment for under 5	HIV incidence (p=0.0001), pneumococcal conjugate-based vaccine (p=0.001), incidence of malaria (p=0.001) and diarrhoea treatment (p=0.002) could significantly predict COVID-19 infection in SSA. However, TB incidence (p=0.86) and smoking prevalence (p=0.53) were not statistically associated with COVID-19 infection.
Ortiz-Fernández and Sawalha29	Africa/global	General	Genetics	2504	Susceptibility	Lower expression of ACE2 and type II transmembrane serine protease (TMPRSS2) genes	Africans were reported to have lower expression levels of ACE2 and TMPRSS2, suggesting a lower susceptibility for SARS-CoV-2 infection in the African populations.

CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; CRD, chronic respiratory disease; CVD, cardiovascular diseases; DM, diabetes mellitus; GDP, gross domestic products; HTN, hypertension; TB, tuberculosis.