Health officials are releasing the first nationally representative estimate of how many U.S. adults have chronic fatigue syndrome: 3.3 million.

Research in U.S. veterans provides fresh evidence that long COVID-19 can happen even after breakthrough infections following vaccination.

President Joe Biden is ordering a new national research push on long COVID, while also directing federal agencies to support patients dealing with the mysterious and debilitating condition.

Experts say it's too early to know whether people infected with the omicron variant will develop long COVID.

Omicron's race across the globe has amped up concerns about long COVID, which some estimates suggest affects a third of COVID-19 survivors.