A new population-based study from Spain reveals that nearly 23% of people infected with COVID-19 between 2021 and 2023 went on to develop long COVID, and for more than half of them, the symptoms persisted for over two years.
The findings, published in BMC Medicine, highlight the long-term impact of the pandemic on health and quality of life.
The study was led by researchers at ISGlobal, in collaboration with the Germans Trias i Pujol Research Institute (IGTP), and was part of the European END-VOC project.
Unlike earlier studies that mainly focused on hospitalized patients, this research used data from the general population, providing a clearer picture of long COVID’s prevalence and risk factors.
What Is Long COVID?
Long COVID refers to a range of symptoms that continue for at least three months after the initial infection. These can include:
- Fatigue and exhaustion
- Breathing difficulties
- Digestive problems
- Neurological symptoms like brain fog or memory issues
- Muscle and joint pain
Researchers followed 2,764 adults from the COVICAT cohort, a long-term health study of people living in Catalonia, Spain. Participants completed detailed health surveys in 2020, 2021, and 2023, and provided blood samples and access to their medical records.
Key Risk Factors for Long COVID
The study identified several factors that increase the risk of developing long COVID:
- Being female
- Having a severe COVID-19 infection
- Having pre-existing chronic conditions, particularly asthma
- Obesity
- High levels of IgG antibodies (a sign of immune system overactivation after infection)
Marianna Karachaliou, one of the study’s co-authors, noted that high IgG antibody levels before vaccination were linked to a higher likelihood of long COVID. This could suggest that an overactive immune response during the initial infection may contribute to long-term symptoms.
Protective Factors
Not all outcomes were negative—researchers also found certain factors that seemed to protect people from developing long COVID:
- Receiving a COVID-19 vaccine before infection
- Maintaining a healthy lifestyle, including regular exercise and getting enough sleep
- Being infected after the Omicron variant became dominant, likely because those infections tended to be milder
Long COVID Comes in Different Forms
By analyzing the types of symptoms reported, the team was able to group long COVID into three subtypes:
- Neurological and musculoskeletal symptoms – such as fatigue, brain fog, and muscle pain
- Respiratory symptoms – including chronic cough and difficulty breathing
- Severe multi-organ symptoms – affecting multiple parts of the body and often more disabling
Notably, 56% of long COVID patients still had symptoms two years after infection, underlining how persistent and disabling the condition can be.
“This study shows that a significant portion of the population continues to suffer from long COVID,” said Judith Garcia-Aymerich, ISGlobal researcher and senior author of the study. “It can affect their health, work, and overall quality of life.”
Dr. Manolis Kogevinas, lead author, emphasized the value of a population-based study to accurately capture the condition’s scope and contributing factors.
The research also stresses the need for international cooperation to understand how these findings apply in other countries, especially as the virus and public health responses evolve.
Rafael de Cid, scientific director at IGTP, highlighted the study’s importance as we mark five years since the beginning of the COVID-19 pandemic: “We’ve come a long way in understanding the disease, but this study reminds us of the ongoing impact—particularly in mental health, employment, and daily life.”
He also credited the COVICAT volunteers and healthcare staff for their vital role in making this research possible, especially during the challenging early years of the pandemic.
This study provides one of the clearest pictures yet of how widespread and long-lasting long COVID can be. With nearly 1 in 4 infected people affected—and more than half still suffering two years later—the findings highlight the urgent need for more support, long-term care, and continued research into the causes, prevention, and treatment of this still-mysterious condition.
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The research findings can be found in BMC Medicine.
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