"Aspirin use can cause serious harms, and risk increases with age," task force member Dr. John Wong, a primary-care expert at Tufts Medical Center, said.
Common side effects of COVID-19 vaccines, which tend to be minor and short-term, include pain and swelling at the injection site, fever, tiredness, chills or a headache.
The findings could transform how doctors prescribe aspirin.
Researchers found aspirin appeared to stimulate a part of the cells that clear debris in mice brains.
A study found that taking anti-platelet drugs such as aspirin prevented a fifth of recurrent heart attacks and strokes but also led to about 3,000 excess-bleeding deaths annually in Britain alone.