The long-term effects in some people with COVID-19 are still poorly understood. This new research used large-scale data to understand how these effects differ based on the severity of the initial infection and how these change over time.

The challenge

Over 400 million people worldwide have contracted COVID-19 within the last two years. Given this enormous scale, health care experts are trying to understand the long-term impact of the disease on individuals. So-called ‘long COVID’ can take many forms, with symptoms including fatigue, shortness of breath and problems with concentration.

Much of the research done on the long-term effects of COVID-19 has focused on the minority of people who were admitted to hospital. This means we do not have a comprehensive understanding of the majority of cases.

Small cohort studies of long COVID have highlighted that patients with mild disease can still struggle with persistent symptoms. However, it is difficult to estimate how common this is from small studies, particularly those that rely on self-reported data, and there has been little research to compare the burden of long-term effects based on the severity of the initial infection.

The solution

Research funded through BREATHE, the Health Data Research Hub for respiratory health, used a GP database of 456,000 people in England to understand the effects after COVID-19. The study focused on patients who were either hospitalised or treated in the community. They were compared with people who had never been infected with COVID-19, to understand healthcare use during the pandemic, and a pre-pandemic cohort of people with influenza, to understand the effect of other respiratory infections.

The study, published in the British Medical Journal, also looked at whether patient outcomes changed before and after vaccination, which is the first time this has been done.

Impact and outcomes

The study found that people had higher GP consultation rates following a COVID-19 diagnosis than people with influenza or those who never had COVID-19. The most common reasons for patients not hospitalised for COVID-19 to see a GP were loss of smell or taste, venous thromboembolism (blood clots), lung fibrosis (tissue scarring that causes shortness of breath) and muscle pain.

For these people, the rates of some conditions decreased over time, but anxiety and depression, abdominal pain, diarrhoea, general pain, nausea, chest tightness, and tinnitus persisted throughout follow-up. The rates of GP consultations for most reasons decreased after vaccination in this group.

Understanding the nature and burden of long COVID across different patient groups will be essential for rehabilitating patients effectively. The researchers will use this dataset to probe further into subgroups of people, such as the impact on those with respiratory or cardiovascular disease.

Dr Hannah Whittaker, from Imperial College London, who was the lead author on the paper, said:

“Not much was known about long COVID outcomes. Those studies that had published were based on patients hospitalised with COVID or were using data that was self-reported or didn’t have that much follow-up. So we wanted to use primary care data to study milder COVID patients where there’s less of a subjective bias.”

Impact committee

The impact committee thought this was an important study that highlighted the potential value of analysing large routine datasets. They also added that the researchers had carefully thought through their approach for comparing the different groups of people.

Read the full paper