A pair of new studies in Nature Communications discuss long COVID, with a Norwegian study finding similar rates after infection with the Delta and Omicron variants in adults, and a Swiss study identifying low socioeconomic status and chronic conditions such as asthma as risk factors for persistent symptoms among teens.
Fatigue, shortness of breath
Norwegian Institute of Public Health researchers led a study of 1,323,145 people aged 18 to 70 years living in Norway who tested positive (57,727) or negative (105,297) for COVID-19. The team analyzed data from the Nordic National register, which is based on medical records of healthcare services available to all residents.
Participants with Omicron infections (13,365 people) were generally younger, more highly educated, had fewer underlying illnesses, and were more often vaccinated than those with Delta cases (23,767).
Among uninfected participants and those not tested, 17.9% and 10.3% tested positive during follow-up and weren't censored in the main analyses and in the sensitivity analyses, respectively. In the combined groups, 10.9% tested positive and were censored in analyses from the date of a positive test.
The adjusted prevalence of post-infection symptoms was 5 to 250 per 10,000 people and was generally higher for those included in the main analyses (Omicron, Delta, uninfected) than for untested participants included in the sensitivity analyses.
Participants infected with Omicron were at comparable risk of long-COVID symptoms as those with Delta infections 14 to 126 days after diagnosis, including during the acute (14 to 29 days), sub-acute (30 to 89 days), and long COVID (90 days or later) phases. Symptoms included fatigue, cough, heart palpitations, shortness of breath, anxiety/depression, and brain fog.
Both Delta- and Omicron-infected participants particularly experienced a 20% to 30% higher rate of post-COVID fatigue and a 30% higher rate of shortness of breath, compared with those who tested negative (fatigue hazard ratio [HR], 1.29; shortness of breath HR, 1.29). Omicron patients, though, had a lower rate of shortness of breath (HR, 0.77).
At 90 or more days, relative to patients with Delta infections, those with Omicron cases had lower odds of reporting any symptom (43 fewer per 10,000 people) and musculoskeletal pain (23 fewer per 10,000). A symptom analysis implied that 43 fewer Omicron-infected participants per 10,000 would visit their doctor with any symptom, compared with 10,000 with Delta cases.
The death rate during follow-up was low, at 0.07%, 0.05%, and 0.14% for participants infected with Omicron, those with Delta cases, and those who tested negative or weren't tested, respectively.
"Our findings suggest that the acute and sub-acute burden of post-covid complaints on health services is similar for Omicron and Delta," the study authors wrote. "The chronic burden may be lower for Omicron vs Delta when considering musculoskeletal pain, but not when considering other typical post-covid complaints."
Teens with long COVID
In Switzerland, Geneva University Hospitals researchers tested children aged 6 months to 17 years (average age, 10.2 years) who were part of the SEROCoV-KIDS cohort study for SARS-CoV-2 antibodies from December 2021 to February 2022, before Omicron became predominant in Geneva. Parents completed a questionnaire on their child's symptoms lasting more than 12 weeks.
Of 1,034 children from 612 households tested, 55.1% were seropositive (had SARS-CoV-2 antibodies), indicating previous COVID-19 infection. After adjustment, among seropositive participants, 9.1% had persistent symptoms, compared with 5.0% of those who were seronegative.
Only adolescents were at substantial risk of long-COVID symptoms (8.3% vs 0.0% among 6- to 11-year-olds and 4.2% among those aged 0 to 5 years). Risk factors for lingering symptoms were older age, having a lower socioeconomic status, and having a chronic health condition, particularly asthma. Sex was not tied to long COVID symptoms.
Relative to seronegative patients, those who were seropositive more often had symptoms such as abdominal pain, trouble concentrating, loss of smell, runny nose, muscle pain, breathing difficulties, headache, and constipation. Seronegative children had more anxiety, lower moods, and dermatologic symptoms such as rash. Only abdominal pain, loss of smell, and constipation, however, were significantly more common in seropositive children.
The authors noted that long COVID could have long-term consequences on health, social, and academic outcomes, which the pandemic has already worsened. The contribution of lower socioeconomic status to long-COVID prevalence may be explained, they said, by greater exposure to SARS-CoV-2, higher susceptibility to infection, higher rates of underlying illnesses, and healthcare disparities.
"Our findings show that a significant proportion of seropositive children, particularly adolescents, experienced persistent COVID symptoms," the researchers wrote. "While there is a need for further investigations, growing evidence of pediatric post-COVID urges early screening and primary care management."