This week, the 2-year follow-up data from the Zurich SARS-CoV-2 Cohort has been published in the BMJ by Tala Ballouz and co-authors from the Epidemiology, Biostatistics and Prevention Institute of the University of Zurich. The researchers aimed to evaluate longer term symptoms and health outcomes of Long COVID patients in the Zurich Cohort of patients that have been infected with SARS-CoV-2.
In this analysis, 1106 adults with a confirmed SARS-CoV-2 infection who were not vaccinated before infection and 628 individuals who did not have an infection were included. The participants filled out a questionnaire to assess if they still experience COVID-19-related symptoms after 6, 12 and 18 months (self-reported health status), how severe their impairment is and which symptoms they are suffering from. By comparing the outcomes of patients with a confirmed infection with those of patients who have not been infected, the risk of having symptoms at 6 months after infection was evaluated.
17% of participants do not report a full recovery 24 months after the infection
When analyzing people who had a SARS-CoV-2 infection, the chance to recover seemed to be the highest within the first year and decreased afterwards. At 6 months 23% of the participants had reported to be not fully recovered, at 12 months the number decreased to 19%. At 24 months 17% of patients still reported that they did not fully recover. However, most participants stated that they experienced a continued recovery (68%) or at least an overall improvement (14%) since the beginning of the study. Only 5% of patients experienced a worsening of their health status and 4% had better and worse episodes during the course of the study.
The self-reported severity of symptoms (mild, moderate, severe) either decreased or remained unchanged for most symptoms. The most common symptoms at all time points were fatigue, post-exertional malaise, changes in taste and smell, dyspnea and cognitive impairment. Interestingly, individuals who already reported Long COVID-like symptoms at baseline were more likely to report that they have not recovered after 6 months. This highlights that it is important to identify individuals who are at higher risk of developing Long COVID due to preexisting conditions and to provide prevention and treatment options for them.
The risk of having developed symptoms at 6 months was approximately 17% higher when comparing individuals that had been infected with SARS-CoV-2 with those that have not. The excess risk for each symptom is presented in the Figure below.
Proportion of each symptom reported at 6 months by participants with and without infection and excess risk for developing these symptoms. The excess risk (adjusted risk difference) was estimated based on inverse probability weighted generalized models and adjusted for age, sex, body mass index, smoking status, education level, monthly income, and presence of hypertension, diabetes mellitus, cardiovascular, respiratory, or chronic renal disease, current or past malignancy, and immune suppression.
The results of this study are in agreement with previously published studies on long term outcomes after a SARS-CoV-2 infection, albeit being in the lower bound of what has been reported so far (22–75% of people who have not recovered at 12–24 months). This could be explained by varying study populations (other studies might include more/focus on patients who were hospitalized with COVID-19 and are therefore more vulnerable to long term symptoms) or by the fact that the present study distinguishes whether symptoms are related to COVID-19 (as assessed by the participant) or not.
The slow recovery that was observed between 12–24 months could indicate a progression into chronic health problems. However, the overall rates of recovery and overall improvement of symptoms might give some hope to those affected by Long COVID.
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