‘Long Covid' may be affecting people in four different ways, according to a review into the long-lasting impact of Covid-19 infection.
This could explain why some people with persistent symptoms are not being believed or treated, the report suggested.
There could be a huge psychological impact on those living with long-term coronavirus, the National Institute for Health Research study said.
Some people are still suffering symptoms seven months after infection, it found.
And those who had a mild illness at the start can have worse ongoing symptoms than patients who needed intensive care treatment.
Even children can suffer, researchers said.
Meanwhile, some people are living with a "rollercoaster of symptoms" that "move around the body".
Researchers who reviewed the available evidence said ongoing Covid symptoms examined reports from people of all ages and backgrounds.
They said that it cannot be assumed that people who are at lower risk of severe illness and death from Covid-19 are also at low risk of ongoing Covid.
Academics said that more work is needed to help those who are suffering as they said that many are "not believed" when they seek help.
Ongoing symptoms can include breathlessness, chronic fatigue, "brain fog", anxiety and stress.
Meanwhile, others may have suffered permanent organ damage.
Some have reported "floating" symptoms whereby they suffer an illness linked to one part of the body - such as the respiratory system, the brain, cardiovascular system and heart, the kidneys, the gut, the liver or skin - which later abates only for new symptoms to arise in a different part of the body.
Such a wide range of symptoms, and different presentations of illness, mean that it is hard for doctors to diagnose, which means that it is equally difficult for patients to access the appropriate care, they added.
They also said that they did not like the term "long Covid" because it may mean that some patients who are struggling with ongoing after-effects are being missed.
Ongoing Covid may not be one illness but four different syndromes, they added.
These have been broadly categorised as: post intensive care syndrome, post viral fatigue syndrome, permanent organ damage and long term Covid syndrome.
Some may suffer these simultaneously.
They called for anyone who believes they are suffering long-term after-effects to be logged as such in their NHS records, and the health service should adopt an approach of a "working diagnosis" to help those in need.
Academics stressed that the understanding of the effects are still at an early stage as they called on people living with the after-effects to get involved with research.
