In May 2020, the World Health Organization (WHO) published a review of existing studies and meta-analyses (analyses of multiple studies) to assess what is known about the relationship between smoking tobacco and COVID-19. The study specifically looked into how smoking tobacco impacts the risk of COVID-19 infection, hospitalization from COVID-19, and severe infection outcomes, which included intensive care unit (ICU) admission, use of ventilators, and death. 

With the limited and mixed evidence available, the WHO found that smoking may be associated with a higher risk of more severe disease and a higher risk of death among hospitalized COVID-19 patients. 

Authors of a 2020 article in The Lancet suggested mechanisms that may explain why tobacco users may be at a higher risk for the disease: 

1. Smoking impairs the immune system and smokers are known to be at a higher risk of developing other infections, such as tuberculosis, influenza, and another coronavirus, the Middle East respiratory syndrome. 
2. Smokers have been observed to have higher levels of angiotensin converting enzyme 2 (ACE2) receptor, which is the main receptor used by the COVID-19 virus to enter the lungs and cause infection. 

However, the risk and possible mechanisms for developing COVID-19 among smokers have not been confirmed and more research is needed. The WHO found no peer-reviewed, population-based studies that specifically evaluated the risk of COVID-19 infection and hospitalization among smokers, indicating the need for more research.

The call for more research on smoking and COVID-19 has also been prompted by unexpected data showing a lower prevalence of hospitalized smokers than non-smokers in China, Germany, and the United States. The quality of this data is uncertain, and there are a number of reasons that this could be the case that research is exploring. 

Nicotine has, however, been considered as a potential therapy for preventing COVID-19. Among the harmful components of cigarette smoke, there is evidence that nicotine, by itself, has anti-inflammatory effects and can prevent acute lung injury. A clinical trial to study nicotine and COVID-19 is in progress. However, the established negative health outcomes of smoking can not be overlooked and make it difficult to study nicotine for prevention or treatment through smokers.

Current research on smoking tobacco and COVID-19 infection is limited due to the difficulty of collecting information on smoking history under emergency circumstances. Studies have also not defined “disease severity” consistently, making it difficult to track disease outcomes across studies. Additionally, more research is needed that differentiates between e-cigarette, tobacco use, and the length of tobacco use. 

For researchers to evaluate the risk of infection and hospitalization between smokers and non-smokers, well-designed, population-based studies are needed. Such studies provide large enough sample sizes that risk factors like age, race, sex, and other chronic diseases can be accounted for. 

Despite the limited information known about COVID-19 and smoking tobacco, smoking is known to increase the risk of developing other non-infectious diseases, such as lung cancer and cardiovascular disease. These diseases are known to increase your risk of COVID-19. Health experts agree that tobacco prevention and smoking cessation efforts should continue.