Fatigue, neurological, and cognitive symptoms after COVID-19 - a nationwide matched cohort study in Denmark

To investigate if COVID-19 increases the odds of fatigue, headache, dizziness, concentration difficulties, and memory impairment as well as at least three of these symptoms, at <4 weeks, 4-12 weeks, and >12 weeks after COVID-19. Additionally, we investigated whether symptoms were influenced by severity of COVID-19, sex, and pre-infection COVID-19 vaccination.

This study utilised data from the DanishBiCoVac cohort and national registers. The BiCoVac cohort collected information about symptoms through four questionaries distributed between May 2021 and May 2022. Participants with COVID-19 were matched to participants without COVID-19.Three matching samples were created according to time since COVID-19. Logistic regression was performed for the association between COVID-19 and each outcome.

Participants with COVID-19 within 0-4 weeks had higher odds of reporting all outcomes compared to participants without COVID-19. Between 4 and 12 weeks after COVID-19, the odds of symptoms were also higher, although attenuated. After 12 weeks, participants with COVID-19 also had higher odds of symptoms except for concentration difficulties compared to those without COVID-19. Odds for symptoms were highest for participants reporting severe infection. Prior COVID-19 vaccination might weaken the association while no clear modification was found for sex.

Participants with COVID-19 had higher odds of all outcomes, especially within the first 4 weeks. After 12 weeks, the ORs were attenuated but still indicated an association for all outcomes except concentration difficulties. Individuals vaccinated against COVID-19 tended to report fewer symptoms after COVID-19. Participants with severe COVID-19 had the highest odds of symptoms.