Long COVID incidence and severity no worse than post viral syndrome following seasonal influenza, study suggests
In the highly vaccinated population of Queensland exposed to the Omicron variant, long COVID appears to manifest as a post-viral syndrome of no greater incidence or severity than seasonal influenza, according to new research being presented at this year's European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Copenhagen, Denmark (15-18 April).
The study by Queensland Health researchers suggests that despite the similarity of clinical outcomes after COVID-19 and influenza, long COVID's impact on public health systems is likely to stem from the volume of those infected with SARS-CoV-2, rather than the severity of long COVID symptoms.
Long COVID is a complex, multi-system condition that develops during or after having COVID-19, and is used to describe symptoms that continue for 4-12 weeks and longer-term sequelae beyond 12 weeks known as post-COVID syndrome.Long COVID has the potential for a substantial impact on society, from increased health care costs to economic and productivity losses.
Between 5% and 10% of COVID-19 cases in Australia are thought to result in long COVID (symptoms persisting for more than 3 months), and it affects people in different ways. Breathlessness, a cough, heart palpitations, headaches, and severe fatigue are among the most prevalent symptoms.
To understand more about long COVID's potential impacts on the Australian state of Queensland, researchers surveyed adults (aged 18 years or older) with PCR-confirmed infection for COVID-19 and influenza in Queensland between 12 and 25 June, 2022.
Laboratory reporting for COVID-19 and influenza is recorded in the Queensland Department of Health's Notifiable Conditions System (NoCS), so the study is a census of all individuals in Queensland who tested positive to COVID or influenza during that period.
At the time, more than 90% of the population of Queensland had been vaccinated against COVID-19 before the community first experienced widespread transmission of the Omicron variant in 2022.
During concurrent waves of Omicron and influenza that occurred in mid-2022, 2,195 adults diagnosed with COVID-19 and 951 adults diagnosed with influenza were followed for 12 weeks and asked about ongoing symptoms and functional impairment using a questionnaire delivered by SMS link to a survey.
Of those diagnosed with Omicron, a fifth (21%, 469) reported ongoing symptoms at 12 weeks and 4% (90) reported having moderate to severe functional limitations in everyday life.
Similarly, around a fifth (23%, 214) of adults diagnosed with influenza reported ongoing symptoms and 4% (42) reported moderate to severe functional limitations.
After controlling for influential factors including age, sex, First Nations status, vaccination status, and socio-economic profile (based on postcode), the analysis found no evidence to suggest that adults with Omicron were more likely to have ongoing symptoms or moderate to severe functional limitations at 12 weeks after their diagnosis than adults who had influenza.
Interestingly, the analyses suggests that younger age groups and non-indigenous populations were more likely to report moderate to severe functional limitations after influenza than Omicron.
"In our highly vaccinated population, the public health impact of Long COVID does not appear to result from any unique property of SARS-CoV-2. Rather, the impact results from the sheer number of people infected over a short period of time," says Dr. John Gerrard, Queensland's Chief Health Officer.
Despite the important findings, the study has several limitations including that it was observational and can't prove causation and it can't rule out the possibility that other unmeasured factors such as underlying illness and influenza vaccination status may have influenced the results. The researchers also note the growing evidence that the risk of long COVID has been lower during the Omicron wave compared with earlier SARS-CoV-2 variants, and because the vast majority of people in Queensland were vaccinated when the Omicron variant emerged, the lower severity of long COVID could be due to vaccination and/or the Omicron variant.
More information: Is long COVID really the next public health crisis? Post-COVID outcomes compared with influenza in Australia, European Congress of Clinical Microbiology & Infectious Diseases (ECCMID), 2023.