Aspirin takers were less likely to be placed in the intensive care unit (ICU) or hooked up to a mechanical ventilator, and they were more likely to survive the infection compared to those who were not taking aspirin, they added.
The study, published in the journal Anesthesia and Analgesia, provides "cautious optimism," for an inexpensive, accessible medication with a well-known safety profile that could help prevent severe complications.
"This is a critical finding that needs to be confirmed through a randomized clinical trial," said study leader Jonathan Chow from the University of Maryland in the US.
"If our finding is confirmed, it would make aspirin the first widely available, over-the-counter medication to reduce mortality in Covid-19 patients," Chow added.
To conduct the study, the research team culled through the medical records of 412 Covid-19 patients, age of 55 on average, who were hospitalised over the past few months due to complications of their infection.
About a quarter of the patients were taking a daily low-dose aspirin (usually 81 milligrams) before they were admitted or right after admission to manage their cardiovascular disease.
The researchers found aspirin use was associated with a 44 per cent reduction in the risk of being put on a mechanical ventilator, a 43 per cent decrease in the risk of ICU admission and - most importantly - a 47 per cent decrease in the risk of dying in the hospital compared to those who were not taking aspirin.
The patients in the aspirin group did not experience a significant increase in adverse events such as major bleeding while hospitalized.
Doctors often recommend a daily low-dose aspirin for patients who have previously had a heart attack or stroke caused by a blood clot to prevent future blood clots.
Daily use, however, can increase the risk of major bleeding or peptic ulcer disease.
"We believe that the blood thinning effects of aspirin provides benefits for Covid-19 patients by preventing microclot formation," said study co-author Michael A Mazzeffi.
"Those at increased bleeding risk due to chronic kidney disease, for example, or because they regularly use certain medications, like steroids or blood thinners, may not be able to safely take aspirin," he added.