One of the primary manifestations of COVID-19 is respiratory disease.  ACE2 expression was assessed in human airway epithelial tissue to better understand how SARS-CoV-2 interacts. with these cells. Studies included:

- ACE2 expression in healthy nonsmokers
- ACE2 expression in smokers
- ACE2 expression modulation by air pollution
- ACE2 expression modulated by miRNA (miR-1246)
- ACE2 expression in basal cells from the large and small airway epithelia of healthy nonsmokers

ACE2 Expression in Human Airway Epithelial Tissue

The authors identified 19 peer-reviewed papers (16 from China, 1 from Korea, and 2 from U.S.) published before April 28, 2020 on COVID-19 patients with data on smoking behavior. The analysis consisted of 11,590 COVID-19 patients, 731 (6.3%) with a history of smoking. Among the patients with a history of smoking, 29.8% experienced COVID-19 progression, compared to 17.6% non-smoking patients who experienced disease progression (OR 1.91, 95% CI 1.42-2.59). 
*"There was moderate heterogeneity among the studies (I2=38%, p=.048) and no significant evidence of publication bias (Harbord’s p=.813, Peters’ p=.941)."

Smoking Is Associated With COVID-19 Progression: A Meta-analysis

Researchers from Stanford University conducted a cross-sectional survey online of U.S. adolescents (13-24 years old) to assess if e-cigarette and cigarette usage increases the risk of being infected with COVID-19.  There were 4,351 respondents to the survey.  It was found that past 30 day dual users (use both e-cigarettes and cigarettes only within the last 30 days) were 6.8 times more likely to test positive for COVID-19.  Ever users of e-cigarettes (use only e-cigarettes) were five times more likely to test positive for COVID-19, while ever dual users (use both e-cigarettes and cigarettes) were seven times more likely to test positive for COVID-19.  


E-cigarette users and dual users are most likely at higher risk for being infected with COVID-19 because being exposed to nicotine and other chemicals within e-cigarettes has a negative effect on respiratory health, specifically on proper lung functioning.  Additionally, the act of sharing e-cigarette devices is common among adolescent e-cigarette users, serving as a potential pathway of infection from one individual to another.  Considering that e-cigarette usage is very widespread in the U.S., especially among adolescents, it can be concluded that adolescent e-cigarette usage is further exacerbating the COVID-19 pandemic.  

E-Cigarette and Cigarette Use is Associated with a Higher Risk of COVID-19

Michigan State University

- smoking
- high BMI
- old age
- congregate housing
- environmental conditions
- Immune system conditions

Risk Factors For COVID-19

Smoking as a Risk Factor for COVID-19

COVID-19 comorbidities are high risk conditions that put patients at greater risk for infection and negative outcomes. Some COVID-19 comorbidities have been found to be: 
- Cancer 
- Cardiovascular Disease
- Diabetes
- Digestive Diseases
- HIV
- Hypertension
- Immunological Disease
- Liver Injury
- Obesity
- Renal disease
- Respiratory System Disease

COVID-19 Patient Comorbidities

The spread of the SARS-CoV-2 virus has produced or highlighted disparate outcomes of different types between population groups all over the world. Health disparities can highlight inequitable access, treatment, etc. within a country or state and often indicate the need for public health intervention.

Disparate COVID-19 Outcomes

Varying environmental conditions could increase the risk for some groups of individuals to be exposed to COVID-19. Example environmental conditions include:   
 - Rain 
 - Wildfires

Impact of Environmental Conditions on COVID-19

People with weakened immune systems are at higher risk of getting severely sick from SARS-CoV-2. Because of this, they have the infection for a longer period of time due to their immune system not fighting it off as fast. If you are immunocompromised, the best way to prevent COVID-19 is to avoid being exposed to this virus. Precautions such as washing hands, cleaning surfaces have to be done more frequent for people with suppresed immune systems.

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