The World Health Organization (WHO) declared the severe acute respiratory syndrome coronavirus diseases 2019 (COVID-19) a public health emergency of international concern (PHEIC) on the 30th of January 2020 and further characterized the spread of the novel COVID-19 disease a global pandemic on the 11th of March, 2020 . As at 30th January 2020, there were 7818 total confirmed cases globally with only 82 cases recorded outside China – the epicenter of the pandemic . Between 30th January 2020 and 20th October 2020, over 40.3 million confirmed cases across 217 countries with over 1.12 million deaths was reported globally making the pandemic one of the deadliest in the past two centuries .
Initial findings from early studies pointed towards age with older individuals being particularly at risk, those with non-communicable diseases (NCDs), such as, diabetes mellitus or cardiovascular diseases such as hypertension, respiratory conditions, and or kidney disease . Further studies have led to the discovery that obesity is a plausible risk factor for severe illness, hospitalization and even death from COVID-19 [5, 6].
Obesity is known to be a risk factor for many NCDs  and other medical conditions leading to an increased risk of hospitalization, serious illness, and mortality . In 2009, for example, obesity was highlighted as an independent risk factor for elevated disease severity and mortality for the HINI influenza virus [8–9] and even though the association between obesity and increased disease severity is not novel, empirical knowledge about its association with the novel COVID-19 virus pandemic is important to guide the fast changing efforts being adopted by health systems globally to halt its spread, severe illness, hospitalizations and mortalities. Increasingly, obesity is being identified as a predisposing factor for COVID-19 and this is particularly worrying as obesity affects a large proportion of the world’s population as 39% of adults globally are overweight (BMI ≥ 25.0 to 29.9 kg/m2) and 13% have clinical obesity (BMI ≥ 30.0 kg/m2) [11, 12].
The prevalence of persons with obesity globally is at an all-time high for both higher income countries and low- and middle-income countries . According to Jones-Smith et al  and Jones-Smith et al , more than 70% of persons with overweight/obesity live in low or middle-income countries, and as a country’s economy grows, the burden of persons with obesity shifts to the poor. More worrying is the fact that empirical evidence shows that obesity leads to impaired immunity, chronic inflammation, decreasing lung capacity and reserve making ventilation more difficult, blood that’s prone to clot, and lower vaccine response as recorded previously for some diseases such as influenza, hepatitis B and tetanus, and all of which can worsen COVID-19 illness [12, 16–18]. Moreover, obesity and NCDs in the geriatric population are significantly associated with polypharmacy, which suppresses immunity leading to increased risk of morbidity and mortality in acute infections that occur in COVID-19 patients . These makes obesity especially in an era of a global pandemic, an important phenomenon worth examining.
There are growing empirical literature on the relationship between obesity and COVID-19. For example, in an observational cohort study in the UK which sampled more than 20,000 hospital in-patients with COVID-19, researchers found that obesity was an independent risk factor for high mortality on COVID-19 patients . In another study in France, the prevalence of obesity among adult inpatients with COVID-19 was found to be high and obesity together with other comorbidities were significant in predicting adverse effect and even death for COVID-19 . A study by Tartof, Qian and Hong  has also reported that obesity is a risky predisposing factor for persons who contract COVID-19, while adding that from their study findings obesity stood out from racial, ethnic, or socioeconomic factors when they were controlled for. In that same study, Tartof and colleagues found that data from the 6916 sampled patients in the study revealed that compared with those at normal body mass index (BMI) of 18.5 to 24 kg/m2, the risk of death more than doubled for COVID-19 patients with a body mass index (BMI) of 40 to 44 kg/m2 and nearly doubled again for those with a BMI of 45 kg/m2. This finding by Tartof and colleagues has been corroborated recently by a study in Saudi Arabia by Herbst et al.  who also found that obesity increases the risk of death from COVID-19 by 48%, the risk of hospitalization by 113%, and of needing intensive care by 74%. Herbst et al.  further highlighted a concern that a COVID-19 vaccine may not work for obese people due to the fact that flu vaccines don’t work effectively in people with BMI of more than 30.
Despite the growing evidence on the effect of obesity on COVID-19 treatment outcomes, it is important to note that in the past there have been some conflicting findings in relation to obesity and their effects on treatment outcomes for some respiratory diseases. For example, findings from a study in the United States which used almost 10,000 cases of seasonal influenza did not find any significant evidence of obesity as a risk factor for requiring mechanical ventilation or death  unlike the case in 2009 . Furthermore, Umbrello et al.  have also reported that obesity was associated with increased survival rate for patients with acute respiratory distress syndrome. These conflicting reports in the past makes it relevant today for a strong synthesis and a meta-analysis of evidence to be established for obesity in the global fight against the COVID-19 pandemic.
Literature is littered with scattered pieces of evidence on how obesity put one at risk for adverse outcome of COVID-19. With this growing body of empirical literature owing to the rapid spread of the novel COVID-19 virus with its accompanying mortalities and the increasing growth in the proportion of the world’s population living with obesity, it has become imperative for this study to be conducted to synthetize the evidence, assess the strength of the evidence and obtain a single summary estimate of the effect of obesity on COVID-19 outcomes through a meta-analysis of empirical literature. This study is expected to provide conclusive empirical evidence to guide ongoing measures and programs put in place by health systems globally to halt the spread, hospitalizations and mortalities as a result of the COVID-19 pandemic.