Most people who end up with long-term COVID started with a mild case, new study shows

Sarah Wulf Hanson is lead researcher for Global Health Metrics at the University of Washington and Theo Vos is a professor of health metric sciences at the University of Washington.


The big idea

Even mild covid-19 cases can have large and long-lasting effects on people’s health. That’s one of the key findings from our recent multi-country study on long COVID-19 — or long COVID — recently published in the Journal of the American Medical Association.

Long COVID is defined as the continuation or development of symptoms three months after the initial infection from SARS-CoV-2, the virus that causes COVID-19. These symptoms last for at least two months after the onset without any other explanation.

We found that a staggering 90% of people living with long-term COVID-19 initially experienced only mild illness with COVID-19. After developing prolonged COVID, the typical person experienced symptoms including fatigue, shortness of breath, and cognitive problems such as brain fog—or a combination of these—that affected daily functioning. These symptoms had as severe an impact on health as the long-term effects of traumatic brain injury. Our study also found that women have twice the risk of men and four times the risk of children developing long-term covid.

We analyzed data from 54 studies that reported on over 1 million people from 22 countries who had experienced symptoms of COVID-19. We counted how many people with covid-19 developed clusters of new long-term covid symptoms and determined how their risk of developing the disease varied based on age, sex, and whether they were hospitalized for covid-19.

We found that patients who were hospitalized for covid-19 had a greater risk of developing long-term covid – and of having long-term symptoms – compared to people who had not been hospitalized. However, because the vast majority of COVID-19 cases do not require hospitalization, many more cases of prolonged COVID have arisen from these milder cases despite the lower risk. Among all people with long-term covid, our study found that nearly one in seven still experienced these symptoms a year later, and researchers do not yet know how many of these cases may become chronic.

Why it matters

Compared to covid-19, relatively little is known about long-term covid.

Our systematic multi-country analysis of this condition produced findings that highlight the potentially high human and economic costs of prolonged covid around the world. Many people living with the condition are adults of working age. Being unable to work for many months can cause people to lose income, livelihood and housing. For parents or carers living with long-term covid, the condition can leave them unable to care for their loved ones.

We believe, based on the prevalence and severity of prolonged covid, that it is preventing people from working and therefore contributing to labor shortages. Long COVID may also be a factor in how people losing their jobs have disproportionately affected women.

We believe that finding effective and affordable treatments for people living with long-term covid should be a priority for researchers and research funders. Long COVID clinics have opened to provide specialized care, but the treatments they offer are limited, inconsistent and can be expensive.

What will be next

Long-term COVID is a complex and dynamic condition – some symptoms disappear, then return, and new symptoms appear. But scientists don’t yet know why.

While our study focused on the three most common symptoms associated with prolonged COVID that affect daily functioning, the condition can also include symptoms such as loss of smell and taste, insomnia, gastrointestinal problems, and headaches, among others. But in most cases these additional symptoms occur together with the main symptoms for which we made estimates.

There are many unanswered questions about what predisposes people to prolonging COVID. For example, how do different risk factors, including smoking and high body mass index, affect people’s likelihood of developing the condition? Does being reinfected with SARS-CoV-2 change the risk of long-term COVID infection? It is also unclear how protection against long-term covid changes over time after a person has been vaccinated or boosted against covid-19.

COVID-19 variants also present new conundrums. Scientists know that the Omicron variant is less lethal than previous strains. Initial evidence shows a lower risk of long-term COVID from Omicron compared to previous strains, but far more data is needed.

Most of the people we studied were infected with the deadlier variants that circulated before omicron became dominant. We will continue to build on our research on long-term COVID as part of the Global Burden of Disease study – which makes estimates of death and disability from all diseases and injuries in all countries of the world – to get a clearer picture of how COVID-19’s long-term toll changed when omicron arrived.

The conversation

This article has been republished from The conversation under a Creative Commons license.

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