Study design and study population
The study population originates from the population-based birth cohort BAMSE. The participants were recruited in 1994–1996, when all children born in four pre-defined municipalities in the northwestern and central parts of Stockholm, Sweden were identified through the population register and invited to participate (n = 7,221). Of these, 477 could never be reached and 1256 were excluded based on to pre-defined exclusion criteria: the family planned to move within one year of the study start, the parents had insufficient knowledge of the Swedish language, the family had a seriously ill child, or a sibling was already recruited into the study. In total, 5488 children were eligible. Of these 4,089 (75%) agreed to participate and were included in the cohort.
The participants have been followed through repeated questionnaires and clinical examinations. The present study is based on data from a follow-up at participant age 22–24 years (conducted in 2016–2019, i.e., “pre-pandemic”), referred to as the “24-year follow-up” [26] and part four of a COVID-19 focused follow-up (participant age 27–30, conducted in 2023, i.e., “post-pandemic”), referred to as the “COVID-19 phase 4 follow-up” [20, 27].
The 24-year follow-up included a questionnaire (n = 3,064, 75% response rate) focusing on asthma and allergic symptoms, lifestyle,- and socioeconomic factors, as well as a clinical examination (n = 2,250). The COVID-19 phase 4 follow-up invited participants who completed the 24-year questionnaire and had provided a valid e-mail address (n = 2,981). This follow-up included a questionnaire (n = 2,101, 71% response rate, 59.3% females) focusing on COVID-19, PCC symptoms, general health, and lifestyle factors. The current study population includes all participants who provided information on COVID-19 and PCC symptoms (n = 2,098), Supplement Fig. 1.
Prevalence of post COVID-19 condition (PCC) symptoms among participants with ongoing PCC (n = 62) or previous PCC (n = 166)
The study was approved by the Swedish Ethical Review Authority (Dnr 2020–02922, Dnr 2023-03269-02). All participants provided informed consent when answering the questionnaire.
Definition of COVID-19 and PCC
Past COVID-19 was defined based on the question “Have you ever had COVID-19?” with the response options “No”, “Yes, once”, “Yes”, several times,” and “Do not know.”
Severity of COVID-19 was defined based on the question “How sick were you during the COVID-19 infection? (in case of several infections, base your answer on the most severe)”. The response options were “no symptoms,” “mild symptoms (e.g., symptoms of cold, slight fever),” “severe symptoms (e.g., breathing difficulties, high fever, fatigue),” and “very severe symptoms (required hospital care).”
Participants who reported that they had had COVID-19 once or several times were asked about long-term symptoms through the question “Have you had long term symptoms after the COVID-19 infection (post COVID/long COVID)?” with the response options “No,” “Yes, previous symptoms but no current ongoing symptoms,” and “Yes, ongoing symptoms.” Participants who answered “Yes” to this question were asked to specify previous and ongoing long-term symptoms and their duration (< 2 months, 2–5 months, 6–12 months, or > 12 months).
The long-term symptoms included were: dyspnoea (breathing difficulties or shortness of breath); fatigue (extreme physical and/or mental tiredness); fever (or feeling feverish); altered smell or taste; headache; tachycardia (high resting heart rate or palpitations); cognitive impairment (e.g., memory and concentration difficulties); gastrointestinal problems; muscle weakness; neurological symptoms (e.g., numbness); psychiatric symptoms (e.g., depression, anxiety or feeling down); pain (e.g., chest pain or muscle and joint pain), sleep disorders, hives/urticaria, and blue-red rashes on the toes.
PCC was defined as at least one symptom lasting for at least 2 months after COVID-19 [9].
Participants who reported PCC were also asked about whether they had sought healthcare for their symptoms, whether they had been or currently were on sick leave for PCC, and whether they have received a PCC diagnosis.
Definition of pre-pandemic socioeconomic,- lifestyle, and health-related factors at 24 years
Information on socioeconomic- lifestyle and health-related factors was obtained from the 24-year follow-up prior to the COVID-19 pandemic (2016–2019) (18).
Education level was self-reported and categorized into two categories as no university-level (including primary and lower secondary school, upper secondary school, high school, upper secondary school) or university education (including folk high school, university or college < 3 years and university or college ≥ 3 years).
Occupation was self-reported and categorized into three categories as student, employed, or other (including on parental leave or unpaid leave, unemployed, and other).
Smoking was self-reported and categorized as “Yes” (including daily or occasional smoking) or “No” (including never or previous smoking).
Asthma was self-reported and defined as doctor’s diagnosis of asthma (ever) together with symptoms of breathing difficulties or asthma medication occasionally or regularly in the preceding 12 months (21).
Overweight was determined at the clinical investigation based on measured weight and height and defined as a body mass index (BMI) ≥ 25 kg/m2. For most (259/268) individuals with missing information on BMI, self-reported information on weight and height was available and used to define overweight.
Doctor diagnosed depression was self-reported as ever having received a doctor’s diagnosis of depression.
Wellbeing was defined based on the question “How are you feeling right now?”. The response options “very good” and “great” were grouped and compared with the response options “good,” “quite good,” and “bad,” grouped.
Self-perceived health was defined based on the question “How healthy would you say you are?” The response option “completely healthy” was compared with “quite healthy” and “not very healthy”, grouped.
Enjoying life was defined based on the question “How happy with your life are you at the moment?”. The response options “I am very happy” and “I am mostly happy” were grouped and compared with “I am not very happy” and “I am not at all happy”, grouped.
Physical activity was calculated from self-reported amount (hours/week) of moderate (e.g. bicycling at normal speed, carrying light objects) and vigorous (e.g. lifting heavy weights, aerobics, or high-speed bicycling) physical activity in the last 12 months. Participants were asked about the summer and winter seasons separately and the mean of these values was calculated.
Perceived stress was defined using the perceived stress scale-10 (PSS-10) consisting of 10 questions on how the participant had perceived and handled stress and stressful situations in the preceding month [28]. Each question had five response options from “never” to “very often,” which were given 0 to 4 points (scores reversed for four questions including positive statements), for a total of 0–40 points.
Definition of post-pandemic general health, stress, and changes in lifestyle factors during the pandemic
Wellbeing, Self-perceived health and Enjoying life were assessed using the same questions as in the 24-year follow-up (see above).
Changes in lifestyle factors during the pandemic was defined based on the question: “How do you feel that your habits/health have changed today compared with before the pandemic?” The included lifestyle factors were physical activity, sedentary time, muscle-, neck, or backpain, time spent in nature, healthy dietary habits, alcohol intake, stress, sleep, and health. The response options were “decreased a lot,” “decreased,” “unchanged,” “increased,” and “increased a lot.” For the analyses, the options “decreased a lot” and “decreased” were grouped into “decreased” and the options “increased” and “increased a lot” to “increased.”
Perceived stress was defined as in the 24-year follow-up.
Physical activity was defined as in the 24-year follow-up.
Statistical analyses
Descriptive analyses were used to characterize the study population in terms of background factors and prevalence of previous and ongoing PCC. Differences between groups (No COVID-19 (including “No” and “Do not know”), No PCC symptoms, Previous PCC symptoms, and Ongoing PCC symptoms) were tested using the chi-squared test. Differences in median PSS-10 score and physical activity in relation to these groups were tested using the Kruskal Wallis test. Changes over time in PSS and physical activity were tested using Wilcoxon-matched-pairs signed rank test. Changes over time in general health were tested using the two-sample test of proportion. Pearson’s correlation coefficients between individual ongoing PCC symptoms and post-pandemic wellbeing were calculated. Individuals with missing data for specific variables were excluded from those analyses. All analyses were performed in Stata version 16.1 (StataCorp LLC, College Station, TX, USA). A two-sided p-value < 0.05 was considered statistically significant.