The U.S. National Institutes of Health (NIH) said on Monday that it had launched mid-stage clinical trials to test at least four treatments, including Pfizer's Paxlovid, in patients with symptoms of long COVID.

The studies are designed to evaluate multiple therapies, where the first part of trial will test a longer dosing regimen of the antiviral COVID-19 drug Paxlovid to see if it improves long COVID symptoms.

The complex medical condition involves more than 200 symptoms ranging from exhaustion and cognitive impairment to pain, fever and heart palpitations that can last for months and even years following a COVID-19 infection.

NIH said other parts of the study will also test for brain fog and memory problems related symptoms.

It will use medical treatments like a web-based brain training program called BrainHQ by San Franscisco-based private company Posit Science Corp and Soterix Medical Inc's device that uses a small electric current to stimulate brain activity, the health agency added.

Additional clinical trials are expected to be launched to test not less than seven more treatments, it said.

(Reporting by Pratik Jain in Bengaluru; Editing by Shweta Agarwal)