(NEXSTAR) – Some COVID-19 patients are still feeling the effects of an infection suffered back in 2020.

According to a news release from The Cleveland Clinic, even those who experienced less-severe infections are suffering long-term consequences. We are also learning that, for some with mild infections or asymptomatic initial infections, those symptoms can resurface for months or even years.

“It would be lovely if we could give patients a time frame, just put up with it for six months and it will go away, but we can’t say that at all,” infectious disease specialist Dr. Kristin Englund said in the news release. “Patients are experiencing symptoms two years out and the clock is still ticking.”

Long-haul COVID is often used interchangeably with Long COVID, or post-COVID syndrome, to refer to symptoms lasting longer than the typical two-week timeframe for post-infection recovery, according to Johns Hopkins University.

There is no common set of long-haul symptoms, but according to the Cleveland Clinic, the most frequently reported are “overwhelming fatigue, persistent cough, shortness of breath, heart palpitations, light headedness, brain fog, muscle aches, chronic constipation or diarrhea, lack of appetite and loss of sense of taste and smell.”

The CDC lists 18 potential post-COVID symptoms, adding fever, sleep issues and other conditions to the above.

The wide variety of symptoms also makes standardized treatment for long-haul patients challenging, and vaccinated patients are not completely immune from long-term complications.

The Cleveland Clinic says it is now working to understand how COVID-19 variants may account for different long-haul symptoms.