LOS ANGELES, May 27 (Xinhua) -- A new U.S. research on long COVID suggests it can happen even after breakthrough infections in vaccinated people, and older adults face higher risks for the long-term effects.

       About one-third who had breakthrough infections showed signs of long COVID, according to the study of veterans published Wednesday in Nature Medicine.

       The study reviewed medical records of mostly white male veterans, aged 60, on average.

       Of the 13 million veterans, almost 3 million had been vaccinated last year through October. About 1 percent, or nearly 34,000 people, developed breakthrough infections.

       Another study from the U.S. Centers for Disease Control and Prevention (CDC) found that about one in five adults aged 18 and older in the United States has a health condition that might be related to their previous COVID-19 illness, compared with one in five younger adults.

       Long COVID refers to persistent symptoms or organ dysfunction after acute COVID-19, including cardiovascular, pulmonary, hematologic, renal, endocrine, gastrointestinal, musculoskeletal, neurologic, and psychiatric signs and symptoms, according to the CDC.