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Updated: Jun 29, 2025
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Symptoms before and after COVID-19: a population and case-control study using prospective data.
Carole H Sudre1,2,3, Michela Antonelli1, Nathan J Cheetham4
1School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.
The European Respiratory Journal
|April 4, 2024
Summary
Experiencing symptoms before COVID-19 increases the risk of prolonged illness. Many long COVID patients were asymptomatic before infection, but pre-existing symptoms significantly worsen outcomes.
Area of Science:
- Epidemiology
- Infectious Diseases
- Public Health
Background:
- A significant number of individuals experience prolonged symptoms following acute coronavirus disease 2019 (COVID-19).
- The influence of pre-infection symptoms on the duration of post-acute COVID illness remains an area of investigation.
Purpose of the Study:
- To assess the impact of pre-infection symptoms on the duration and severity of post-acute COVID illness.
- To identify risk factors associated with prolonged COVID-19 symptoms.
Main Methods:
- Survival analysis of 23,452 adults with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, using data from the ZOE COVID Symptom Study app.
- A case-control study matched 1:1 (n=1350 pairs) comparing individuals with long illness (≥8 weeks) versus short illness (<4 weeks), analyzing baseline symptoms (4-8 weeks pre-infection).
Main Results:
- Individuals with pre-infection symptoms had a longer COVID-related symptom duration (median 15 days vs. 10 days).
- Baseline fatigue nearly doubled symptom duration. Pre-infection symptoms doubled the odds of long illness (OR 2.14).
- While many with long COVID were asymptomatic beforehand (67.4%), a significant proportion (32.6%) had baseline symptoms, compared to 18.9% in the short illness group (p<0.0001).
Conclusions:
- Pre-existing symptoms before COVID-19 infection are associated with longer illness duration and increased odds of developing long COVID.
- A substantial portion of individuals with long COVID were asymptomatic prior to SARS-CoV-2 infection, indicating other contributing factors.
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