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"Long flu" emerges as a public health risk

Since the outbreak of COVID-19, a wealth of research has highlighted the virus’s ability to impact various organ systems, leading to a condition known as long COVID, characterized by persistent and often debilitating health issues. 

Recent findings from the Washington University School of Medicine in St. Louis and the Veterans Affairs St. Louis Health Care System have now shown that hospitalization due to seasonal influenza can also result in long-term, detrimental health effects, particularly on the lungs and airways.

Extended health risks 

This study, which compared the long-term health impacts of COVID-19 and the flu, found that patients hospitalized for either condition face increased risks of death, rehospitalization, and various health problems for up to 18 months following infection. Significantly, the greatest risk period extends beyond the first 30 days after initial infection.

“The study illustrates the high toll of death and loss of health following hospitalization with either COVID-19 or seasonal influenza,” said senior author Ziyad Al-Aly, MD, a clinical epidemiologist at Washington University. 

“It’s critical to note that the health risks were higher after the first 30 days of infection. Many people think they’re over COVID-19 or the flu after being discharged from the hospital. That may be true for some people. But our research shows that both viruses can cause long-haul illness.”

Focus of the study 

Published on Dec. 14 in The Lancet Infectious Diseases, the study involved a comprehensive 18-month post-infection analysis, comparing risks of death, hospital readmissions, and 94 adverse health outcomes across major organ systems.

“A review of past studies on COVID-19 versus the flu focused on a short-term and narrow set of health outcomes. Our novel approach compared the long-term health effects of a vast array of conditions,” Al-Aly said. 

Key insights 

“The big answer is that both COVID-19 and the flu led to long-term health problems, and the big aha moment was the realization that the magnitude of long-term health loss eclipsed the problems that these patients endured in the early phase of the infection. Long COVID is much more of a health problem than COVID, and long flu is much more of a health problem than the flu.”

Al-Aly pointed out that while both COVID-19 and the flu lead to long-term health issues, the risks associated with COVID-19 are significantly higher in many organ systems, except for the lungs, where flu poses a greater threat. 

“This tells us the flu is truly more of a respiratory virus, like we’ve all thought for the past 100 years. By comparison, COVID-19 is more aggressive and indiscriminate in that it can attack the pulmonary system, but it can also strike any organ system and is more likely to cause fatal or severe conditions involving the heart, brain, kidneys and other organs.”

COVID-19 outcomes

The study utilized de-identified medical records from the U.S. Department of Veterans Affairs database, including data from 81,280 COVID-19 patients and 10,985 flu patients hospitalized during specific periods.

Mortality risk

The analysis revealed that COVID-19 patients had a 50 percent higher risk of death than those with the flu, equating to about eight additional deaths per 100 persons in the COVID-19 group compared to those with flu. 

Health complications 

COVID-19 was associated with an increased risk of 68 percent of the health conditions studied (64 of 94), while the flu was linked to an elevated risk of six percent of conditions (six of 94), mainly affecting the respiratory system.

Hospital readmission

Over 18 months, COVID-19 patients also faced a higher risk of hospital readmission and ICU admission. The findings underscore the importance of reducing hospitalizations for both viruses to lessen overall health loss in populations.

Study implications 

Al-Aly stressed the significance of vaccinations for both COVID-19 and the flu, especially for vulnerable groups like the elderly and immunocompromised, as they can prevent severe illness and reduce hospitalization and death risks.

Highlighting the long-term impact of these viral infections, Al-Aly concluded: “The idea that COVID-19 or flu are just acute illnesses overlooks their larger long-term effects on human health.” He called for a paradigm shift in how viral infections are perceived, emphasizing their role as major contributors to chronic diseases.


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