Investigating post-COVID complaints after Delta versus Omicron variant infections

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant is associated with less severe acute disease and reduced risk of hospitalization as compared to the previously dominant Delta variant. However, concerns regarding the persistence of long-term complaints, such as those which have been reported for earlier SARS-CoV-2 variants, remain.

Study: Post-covid medical complaints after SARS-CoV-2 Omicron vs Delta variants – a prospective cohort study. Image Credit: Natalya Roshkova /


The increased secondary attack rate with the SARS-CoV-2 Omicron variant as compared to the Delta variant, along with several symptomatic but less severe cases, even among vaccinated individuals, has highlighted the need to better understand the long-term impacts of infection with the Omicron variant. The potential of the Omicron variant to cause temporary and/or persistent coronavirus disease 2019 (COVID-19) symptoms can increase the burden on an already strained healthcare system.

Survey data that has been used to identify symptom persistence patterns in individuals who have recovered from COVID-19 have varied extensively and, as a result, cannot be used to infer consequences regarding potential impacts on healthcare services. Additionally, the accuracy of symptoms and testing is affected by reporting and response biases.

Nordic National register data is medical record data based on healthcare services that are available to all Norweigan inhabitants. Associating this type of medical record data with variant-specific COVID-19 data can help to better understand both the etiology of post-COVID syndrome, as well as the expected burden on healthcare systems.

A new study published on the medRxiv* preprint server discusses whether infection with the SARS-CoV-2 Omicron variant increases the risk of post-COVID complaints as compared to COVID-19-negative individuals and those infected with the SARS-CoV-2 Delta variant. Herein, the researchers also estimated prevalent complaints in the acute, sub-acute, and chronic post-COVID phases three months after the initial diagnosis.

About the study

The study included all Norwegian residents between the ages of 18 and 70 who had tested negative or positive for COVID-19 when the SARS-CoV-2 Delta and Omicron variants were simultaneously circulating throughout Norway. The SARS-CoV-2 variant responsible for all COVID-19-positive cases was identified through sanger or whole-genome sequencing (WGS).

Study participants were categorized as those who tested positive for the SARS-CoV-2 Omicron variant, those who tested positive for the Delta variant, and those who tested negative.

Multiple complaints by the participants were included in the current study, which included fatigue, musculoskeletal pain, shortness of breath, cough, heart palpitations, brain fog, and anxiety/depression. The observations were censored on day 126 of the follow-up, date of death, or emigration.

Study findings

Out of the 3,656,064 individuals who were eligible for the current study, 55,853 tested positive for COVID-19 and were screened for the causative variant, whereas 105,196 tested negative. Those who were infected with the Omicron variant were younger, had fewer comorbidities, had higher education, and were more likely to be vaccinated as compared to those infected with the Delta variant.

A 20% increased rate of post-COVID fatigue, as well as a 40-70% increased rate of post-COVID shortness of breath, was reported for both Omicron- and Delta-infected individuals as compared to those who w negative for COVID-19. The incidence of other post-COVID complaints was similar for those infected with both SARS-CoV-2 variants. Notably, these findings were implied to be independent of vaccination status.

The risk of post-COVID complaints declined 90 days after the initial COVID-19 diagnosis for both Omicron- and Delta-infected individuals. However, a 15% increased rate of fatigue and a 50% increased incidence of shortness of breath were observed at more than 90 days following Delta infection, while no such observation was reported for Omicron infected individuals.


Both the SARS-CoV-2 Delta and Omicron infections were associated with increased risks of fatigue and shortness of breath as compared to individuals who were not infected with SARS-CoV-2.


The current study did not include individuals who tested positive or negative through antigen or other home tests. An additional limitation was that the reverse transcription-polymerase chain reaction (RT-PCR) test that was used to diagnose COVID-19 was conducted during a period of great uncertainty regarding the severity of the new SARS-CoV-2 Omicron variant.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
  • Magnusson, K., Kristoffersen, D. T., Dell'Isola, A., et al. (2022). Post-covid medical complaints after SARS-CoV-2 Omicron vs Delta variants – a prospective cohort study. medRxiv. doi:10.1101/2022.05.23.22275445.

Posted in: Medical Science News | Medical Research News | Medical Condition News | Disease/Infection News

Tags: Antigen, Anxiety, Brain, Brain Fog, Chronic, Coronavirus, Coronavirus Disease COVID-19, Cough, Depression, Education, Fatigue, Genome, Healthcare, Heart, Musculoskeletal, Omicron, Pain, Polymerase, Polymerase Chain Reaction, Respiratory, SARS, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Syndrome, Transcription

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Written by

Suchandrima Bhowmik

Suchandrima has a Bachelor of Science (B.Sc.) degree in Microbiology and a Master of Science (M.Sc.) degree in Microbiology from the University of Calcutta, India. The study of health and diseases was always very important to her. In addition to Microbiology, she also gained extensive knowledge in Biochemistry, Immunology, Medical Microbiology, Metabolism, and Biotechnology as part of her master's degree.

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