Low-doses of aspirin taken before the need for hospital admission due to COVID-19 might have a role in preventing COVID-19 complications, especially arterial thrombosis (a blood clot in an artery) and mechanical ventilation in both hospitalized and non-hospitalized patients. 

However, research on the association between aspirin and COVID-19 is limited, and so far has only been carried out through observational studies which can only show associations, not causal relationships. As a result, more research, particularly randomized control trials which are designed to test causal relationships, are needed to understand the relationship between aspirin and COVID-19 outcomes. 

Aspirin is what is known as a nonsteroidal anti-inflammatory drug (NSAID). NSAIDs are a class of drugs used to reduce fever, relieve pain, and lower inflammation. Aspirin also works as a type of blood thinner called an antiplatelet, which works by reducing your blood cells' ability to clump together to form a clot. As a result, it’s regularly given to patients with coronary artery disease (damage or disease in the heart's major blood vessels) and in those who have a higher than average risk of coronary artery disease. Aspirin has risks, even at low doses — mainly bleeding in the digestive tract or ulcers, both of which can be life-threatening.

Aspirin has been considered and tested as a potential preventative drug against adverse events associated with COVID-19 (eg. arterial thrombosis, mechanical ventilation, ICU admission) since the start of the pandemic. Evidence overall has been promising but is not strong enough to establish a causal relationship between aspirin use and reduced COVID-19 complications. 

For instance, one meta-analysis (a study that collectively assesses the results of multiple previous studies), found that aspirin use was associated with decreased risk of mechanical ventilation, ICU admission, and in-hospital mortality. However, this analysis only assessed five studies that were all observational. Another study found that low-dose aspirin may reduce blood clotting when paired with the anticoagulant (clot-preventing) drug enoxaparin -- more so than low-dose aspirin on its own. 

Some research has also focused specifically on prevention of COVID-19 infection. As a final example, one cross-sectional study found that the proportion of people taking aspirin was lower in the COVID-19-positive group versus the COVID-19-negative group, suggesting a possible association. However, this study was cross-sectional, which is 

However, all of these studies were observational and retrospective -- meaning that they were looking at existing data and were not designed to test a cause and effect relationship. As a result, more research is needed to understand if these associations are, in fact, causal, and not related to some other factor.

A U.S. expert panel (The U.S. Preventive Services Task Force) recommended on Tuesday, October 12, 2021, that people aged 60 or older who are at risk of heart disease but have not yet had a heart attack or stroke should not start a daily low-dose aspirin regimen to prevent a first heart attack because the risk of internal bleeding outweighs the benefits. 

This recommendation stemmed from new data which suggested that the increased risk of bleeding associated with aspirin use occurs relatively quickly after initiating aspirin, with the risk of bleeding going up with age. It also showed that the benefit in reducing heart attacks and stroke in this group might not be as beneficial as originally thought, particularly when weighed against these risks. 

The last time guidance was issued on aspirin use in preventing heart disease was in 2016, and was based primarily on data from the 1980s and 1990s, when controlling for factors like blood pressure was not as common, giving aspirin more room to add value to preventing heart attacks and strokes. 

The data has improved since then and the revised guidance is very specific to one group. Aspirin remains important to take for many, especially anyone who is on aspirin because they’ve already had a heart attack or stroke. The updated guidance essentially just means that people who are not at increased risk for bleeding and are willing to take low-dose aspirin daily are more likely to benefit than people who do not fall in those categories who may have risks from aspirin that outweigh the benefits. Aspirin is not being banned or recommended against at large by any means. In addition, the guidance was specifically developed based on data regarding aspirin and heart disease for guidance surrounding the use of aspirin and heart disease -- not COVID-19.