At the beginning of the pandemic, it was widely accepted that people with Covid-19 would, on average, recover in two weeks – but experts are slowly beginning to realise this isn’t always the case.

The Covid-19 Symptom Study suggests only 52% of people in the UK have recovered within 13 days, meaning hundreds are struggling for longer. Dubbed the ‘long-haulers’, these people are desperate for their voices to be heard when it comes to their experiences of ‘long Covid’.

People suffering long-term include those who had severe cases of coronavirus – and ended up in intensive care – as well as those who had ‘mild’ cases, and either stayed at home, or went to hospital but weren’t in intensive care.

As the virus is still so new, experts are only just beginning to learn what the long-term effects of mild Covid-19 are. The government has launched a study into the long-term health impacts of coronavirus – but only on hospitalised patients. Those who struggled with the virus at home are yet to be examined.

Professor Louise Wain, GSK / British Lung Foundation chair in respiratory research at the University of Leicester, who is involved with the ongoing study, said: “We anticipate that the results of our study may be relevant to individuals who were not hospitalised and who had mild disease, but who might also be suffering from, or at risk of developing, longer-term effects.”

While there’s limited research in the area, we do know people with mild Covid-19 can experience a wide variety of symptoms months after becoming ill. The Covid-19 Symptom Study found a group of people continue to experience fatigue, headaches, coughs, loss of smell, sore throats, delirium, and chest pain after three weeks. In some cases, symptoms come and go, and then return in full force. For others they appear to get better over time, albeit very slowly.

“Now we see a significant proportion of the population with chronic damage from the virus,” Dr Roberto Cosentini, head of emergencies at Papa Giovanni XXIII Hospital in Bergamo, told Sky News.

A small study found some people who tested positive for Covid-19 showed neurological and neuropsychiatric illness – this was the case in both severe and mild cases.

Of 43 patients analysed, 10 had brain disease with delirium or psychosis, 12 had inflammation, and nine had acute disseminated encephalomyelitis (a rare neurological disorder which results in swelling in the brain and spinal cord). Eight had strokes and a further eight had peripheral nerve problems.

In a report on long Covid symptoms conducted in the US by patients themselves, neurological symptoms that cropped up repeatedly included: brain fog, concentration challenges, memory loss, seizures, dizziness and problems with balance, and insomnia. Brain fog and concentration challenges were a more common symptom than cough during most weeks, as was insomnia.

Dr David Strain, a clinician at the Royal Devon and Exeter Hospital and a clinical academic from the University of Exeter, ran a Covid-19 ward for people who didn’t require intensive care treatment for their symptoms.

He tells HuffPost UK there’s a “whole group of people” who had mild Covid symptoms – many of them had little more than a mild flu-like illness or two or three days-worth of illness – that have been “left with neurological effects”.

“We’ve seen people taking incremental steps towards dementia,” he says. Older adults who had normal brain function are now presenting with symptoms in keeping with dementia, he adds, such as slower mental function, challenges with memory and the inability to process simple tasks like cooking a meal.

There have also been patients who presented to hospital with delirium when they first came down with the virus – so sudden confusion, agitation, and derangement. Those individuals would normally get better within a week to 10 days of the infection resolving, says Dr Strain, but in some cases people are still struggling a number of weeks down the line.

Not much is known about the impact on the lungs and heart among those with mild Covid-19, however studies in hospitalised patients have shown these are areas of concern in terms of recovery. Some people have ended up with heart problems and/or lung damage following infection.

A study of 40 non-severe (mild) and 17 severe cases in China revealed 31 patients (54.4%) had abnormal findings on CT scans of their lungs. While the rate of abnormalities was much higher in severe cases (94.1% had abnormalities), in the mild group, 37.5% still showed abnormalities.

Even patients considered asymptomatic – where they show no symptoms at all – have been found to have “significant changes” to their lungs on CT scans.

Treating these issues is hard because the virus is still so new. “Because there’s no similar condition out there, we genuinely don’t know how to treat these people,” says Dr Strain. “One of the most disturbing things about these lasting complications is that they don’t appear to be related to the severity of the disease at the time.”

Dr Strain recalls how two of his patients in their late 30s and early 40s only had mild flu-like symptoms back in March, but both have ended up with “quite significant complications”. One of them is unable to go out walking without experiencing shortness of breath. These effects don’t appear to be limited to a certain age group, he says: “This is affecting anybody.”

More research needs to be done in this area – and in the meantime, those with mild Covid-19 and a long tail of symptoms need to feel supported.

Long-term implications are important to understand because a study on SARS (an illness caused by another type of coronavirus) in Hong Kong found that two years after having it, one in two patients had poorer health outcomes and exercise capacity and only 78% of survivors had returned to work.

The difference is that there were 8,096 SARS cases globally, with 900 deaths. At the time of writing, there were almost 13m confirmed Covid-19 cases globally and 567,000 deaths, with 5.8m people thought to have recovered.

Dr Strain is urging people to “try not to get it [Covid-19] in the first place” and advocates for the use of face masks in public settings. He says those who suspect they caught Covid-19 and are struggling with neurological symptoms like brain fog and confusion should get checked out.

There is some positive news, however. “When it comes to Covid, we know that people are responding to exercise programmes, albeit much slower,” he says, meaning people are gradually building their strength back up after having the virus.

He adds: “We also know that people who got the disease early on are starting to heal – even though it’s [taking] a lot longer than usual.”