The ward had a person falling ill on it. She had been a nurse for 18 years and had cared for patients with respiratory problems. She was scared even though she felt ropey. As the first wave of Covid swept across Britain, people were dying.

On 23 March, the day the prime minister announced the nation's first lock down, Mutesva signed off sick. The infection took hold and made her unable to do anything. She was having a hard time breathing. There were palpitations and pains in her chest. She couldn't get to the shower in time.

She was called to the hospital because of her condition. The woman was sent home after testing positive for Covid. She says she was worried because she lived alone. It is an emergency when a patient has chest pains and is struggling to breathe.

She had her family call her at 9am each day to make sure she was okay. They had to alert the concierge if she didn't reply. She left her door unlocked so they wouldn't be able to get to her. She says she didn't know if she would wake up.

It wasn't the end of the story after the first bout of Covid. Although most people who catch the virus have a mild disease which clears up in a few weeks, Mutesva, 43, was one of those who experienced long- lasting illness. According to the Office for National Statistics, almost 2 million people in the UK are living with long Covid. More than half of the people caught it more than a year ago. A fifth say their symptoms limit their day-to- day activities.

NHS medical staff wearing PPE work in a corridor in a ward for Covid patients.

NHS medical staff wearing PPE work in a corridor in a ward for Covid patients. Photograph: PA Images/Alamy

She returned to work after taking a 10 week break. She was tired, but the chest pains were easing and she was able to walk to the tube station.

Mutesva began on reduced hours rather than returning full-time immediately. She started her first shift after five weeks. It didn't work out. She was told to take another week off by the doctors.

August was when Mutesva was able to see what was wrong. The University College hospital in London had set up a long Covid clinic where she could get her blood oxygen levels checked after she did a simple exercise of standing and sitting. She may have had a specific blood test. There is some evidence that tiny blood clot may underpin some symptoms in some patients, for example by impairing the flow of oxygen into blood in the lungs.

Rivaroxaban is an anti-coagulant that is used to prevent and treat blood clot. Three months later, I was feeling better. They returned when she stopped the drug. When she stopped the treatment worked again but the symptoms came back. The woman had taken four courses of the drug. Her symptoms did not return six weeks after the last course. She's been waiting for a breakthrough. She says she is better than she is.

The illness has had a negative effect on Mutesva. She didn't know if she'd ever be able to manage her previous 12-hour nursing night shifts after she was redeployed. She is worse off each month due to the financial hit. She can't return to Africa to see her family as often as she used to.

Could microclots help explain the mystery of long Covid?

The changes are more positive. Before the H1N1 epidemic, Mutesva was overweight. She has lost 9 stone in the last two years. At the weekends, she walks around the block for half an hour. She says she is more active deliberately. I think it has helped my recovery.

When they became concerned about the number of Covid patients being readmitted to hospital, the long Covid clinic was started. Almost all the Covid patients who had been discharged in the previous month were called to find out what was happening. Half of them sounded unwell enough for the doctors to return them to the hospital.

The "Find and Treat" van is a mobile health clinic that travels around London giving diagnoses and care to homeless and other vulnerable people. Word spread quickly. Patients were asked if they could be sent over. The majority of those were the staff of the health service.

The initial concern was that patients would have problems from Covid such as inflammation in the lungs. The doctors saw a lot of different problems. Patients had severe fatigue, breathlessness that couldn't be explained, palpitations, chest pain, headaches, and a loss of smell. There were a lot of people who were getting infections.

The clinic worked with specialists from different fields to come up with a treatment plan. There weren't many of these clinics when we first started. The people were wondering if it was just a post-viral thing. I said no. For a couple of weeks, this isn't feeling tired. Something more is going on.

Megan Willis, a dance teacher who suffers from long Covid.

Megan Willis, a dance teacher who suffers from long Covid. Photograph: Teri Pengilley/The Guardian

Covid caught Megan in the first wave. In the summer, there was no smell and the cough cleared up. It hit her just before half term. She said she couldn't breathe. I couldn't leave the bed.

The doctors sent her home after putting her on oxygen. Nothing untoward was found in the routine tests. Everything came back normal. She said she knew something wasn't right. You know your body as a dancer. They said that average is really good. I was angry.

After taking a fortnight off, he worked through the winter. She was okay for a while, but then she started gasping for air. Early this year her condition deteriorated. She couldn't walk for a long time. She couldn't carry things. She felt pain in her arms and legs.

There was an appointment at the Covid clinic. She had a breathing disorder. Even though her nose was scanned and found to be fine, she still felt blocked. She was tired after being signed off work. She slept for a long time. She relied on her family and friends to get her daughter to and from school. She said it was terrible. I couldn't do anything because I couldn't drive for a long time.

The clinic arranged for people who had had their breathing knocked sideways by Covid to take a course on breathing therapy. The goal was to retrain the brain to breathe normally again, but the course had other benefits. The community came together. The social side and the mental side were difficult. You look fine, but it's not visible.

The mental toll of her life became so limited that she began taking antidepressants to help with the mental toll. School ended for the summer after a brief return to work.

The prospect of going back to full-on dance teaching in the autumn is daunting. She says she is better than she was in March. The physical fitness she misses most is her sense of smell. I would like to return to where I was. The person I was for 25 years is still there. It's like who am I?

Megan Willis: ‘I can’t let go of the super-fit person I was for 25 years.’

Megan Willis: ‘I can’t let go of the super-fit person I was for 25 years.’ Photograph: Teri Pengilley/The Guardian

Females, middle-aged and people living in more deprived areas are more likely to report long Covid. Health and social care workers are more likely to experience it. People with pre-existing conditions are more likely to be in danger. Many of these people aren't seen by Covid clinics. 70% of the women at the clinic are female, and many are in the higher risk age band. The doctors don't have a lot of patients from poor families.

There are other conditions that muddy the waters when it comes to identifying long Covid in patients. It is easier for a doctor to refer a patient to the clinic if they know the patient was well before Covid. If there is a language barrier, patients from more deprived areas might not be able to see a doctor.

We are definitely seeing a group of people. People who explain their symptoms and get a referral are the ones we see. Efforts are underway to find people in need of help.

Covid was caught by Yvonne Shield as the UK entered its first lock down. A health charity worker used to go to the gym three or four times a week for fitness classes. She was hit hard. She couldn't breathe due to her chest and lungs hurting. Her hair fell out as a result of her headaches and fatigue.

Shield was prescribed antibiotics after a consultation with her doctor. She says she was unwell for a long time, but didn't need to be hospitalized.

Yvonne Shield suffers from Long Covid.

Yvonne Shield: ‘I seemed to be in this zombie state of being very unwell for a long time.’ Photograph: Teri Pengilley/The Guardian

Shield was out of commission for eighteen months. She had brain fog and couldn't think clearly. She did not do a lot around the house. She spent a lot of time sitting down and could feel her joints seizing up. I was told to go out for walks and build myself back up, but it didn't work out that way. I would take a 20-minute walk. I had to learn how to slow down.

Shield was helped to breathe more deeply after taking the breathing course. She had been diagnosed with asthma. Shield says an inhaler prescribed by them changed her life. She says her symptoms got better. They improved and it helped the fatigue.

Shield feels that she is getting better despite her asthma. She says that her journey is a lot slower and more frustrating than she thought it would be. I can't do what I used to. I'm going to get there.

There is no testing for Covid. Patients are assessed to rule out other causes and then identify the components of their illness. The headaches, palpitations and dizziness can be treated with drugs. Breathlessness can be improved with the use of breathing therapy. A lot of patients need psychological support.

Tiredness is one of the most common aspects of long Covid. Some patients have suffered a severe loss of fitness, while others benefit from support to gradually recover. Some people find their symptoms get worse when they try to be active.

One of the most important research questions for us is why some people have worse symptoms than others. There is no single recipe for treatment. Each person has their own approach to the approach.

When he was in his final year at medical school, Krunal went out with his friends to drink and eat. He didn't think much of the drinks at the bar. He became more worried when they moved to a Chinese restaurant. The food wasn't very good. He went back to his flat because he was worried about spreading the virus. He tried some Haribo sweets and they were tasteless. He couldn't smell the garlic. He said he didn't feel unwell, but he thought it was Covid.

He thought his senses would be disrupted for three weeks or so after he had caught the virus. Nothing had changed over the next two months. He thought he had nothing to lose when he tried the random treatments on social media. They didn't make anything different.

The smell training for some patients was recommended by the National Health Service. Every day, the training involves smelling a fixed set of four smells. His sense of smell was shot after he learned that he could still experience some tastes. He kept a daily log to track his progress, but he couldn't find anything to write about. He says he lost motivation when there wasn't anything happening. I wondered if it wasn't going to return.

Dr Clair Vandersteen wafts a tube of odors under the nose of a blindfolded patient in a hospital in Nice, France, to better understand COVID-19-related anosmia.

Dr Clair Vandersteen wafts a tube of odors under the nose of a blindfolded patient in a hospital in Nice, France, to better understand Covid-related anosmia. Photograph: John Leicester/AP

Losing smell was more than an annoyance. His motivation to eat waned. I changed my diet quite a bit. If it had a complex flavour profile, I would only eat it. The spices would be doubled up. The soups tasted the same. It was boring to have a single texture. He says that even milk chocolate was dull.

He was forced to feed himself one meal a day to keep his energy levels up.

There were risks associated with the loss of smell. When he accidentally left the gas on, he didn't know until his mother turned it off.

He was surprised by other things. He didn't like surgery because it produces an awful smell and he didn't like it because he didn't like it. He says it was unpleasant but he couldn't smell it anymore. I now want to pursue surgery.

People who have lost their sense of smell and taste can go to the anosmia clinic. About 10% of what it should be was found by doctors. There was a suggestion of steroids. The drug had a quick impact. The flavours and smells seemed to be different. He liked watermelon and clementines before he took the steroid. Coffee began to smell bad. The scent is still unpleasant. He says that he is sensitive to it.

After he was discharged from the anosmia clinic, he says his sense of smell remained the same. He began to detect more flavours in dishes he had given up on in the spring of this year. This is where I am now. I feel like there is more to this process of recovery yet, even though I think it will come back.

The services that have been pulled together are a priority at the moment. Research will begin to feed into treatments. The Stimulate-ICP trial is one of the most important studies of Covid to date and involves patients, doctors, researchers and industry. It will look at medicines, diagnostics and digital tools to see if they can help.

As long as Covid is around, he will be around. We have to be prepared for this to continue.

Long Covid can be torturous for patients. There is no simple cure for long Covid because it is probably more than one condition. Doctors need to build patients' confidence that they can improve if they are involved in recovery plans.

People are making important recoveries. There are some people who get better with time and others who have a more rocky road, but there are hardly any patients who are better than when we first met them. You will get better with time and the right support.