Study questionnaires
sore throat, nausea, death, fever, diarrhea, fatigue, cough, loss of taste or smell, ache, infection, nasal congestion, headache, breathing difficulties
SORE THROAT, INFECTION, DISEASE
Individual COVID-19 symptoms’ duration and severity were assessed during the study by a specialized questionnaire where the participants were asked to mark weekly whether they had experienced any possible symptoms of COVID-19. The symptom list included: cough, sore throat, nasal congestion, breathing difficulties, fever, muscle or body ache, loss of taste or smell, diarrhea, nausea, headache, and fatigue. If the participants answered “Yes” to any of those symptoms, they were asked to also fill in when the symptoms started and ended. The questionnaire also included questions if the participant had been tested for COVID-19 during the week (free PCR testing was available to all residents via public health care), if they had visited a health center because of their symptoms, and if they had taken any medications for their symptoms. The participants were also asked to record the time and vaccine type if they had received any against COVID-19 during the week. Symptom severity was assessed according to World Health Organization’s Ordinal Scale for Clinical Improvement where the severity of symptoms is graded on a scale of 0–8. The grade 0 refers to no clinical or virological signs of infection, grades 1–2 to ambulatory disease symptoms, grades 3–4 to mild disease requiring medical treatment at a hospital, grades 5–7 to severe disease, and grade 8 to death from the disease.At the start of the study, participants were asked to complete a food frequency questionnaire (FFQ) specially designed for the eating habits of the Swedish population. The recall time was the past six months. The FFQ was semi-quantitative (i.e., included questions on portion sizes). Frequency categories varied from never to three or more times daily. In total 183 food items were listed, though certain items were conditional on previous answers given. Completion time was 30–40 minutes. Nutrient intake was calculated using the Swedish food composition table maintained by the Swedish Food Agency. Daily intake of carbohydrates, protein, fat, fiber, and alcohol were converted to their energy equivalent and results are presented as percent of mean daily energy intake (E%).