Study involving BIPS shows: Persistent symptoms following respiratory infections occur across various pathogens

Not everyone who has a respiratory infection recovers fully. For some people, symptoms persist even after the infection has subsided. Such symptoms, which last more than twelve weeks after the acute phase, are referred to as post-acute infection syndrome (PAIS).

“From severe fatigue and low physical endurance to shortness of breath, there is a wide range of symptoms that can occur with PAIS. These symptoms are often difficult to classify medically and, consequently, difficult to treat,” explains Prof. Dr. Rafael Mikolajczyk, director of the Institute for Medical Epidemiology, Biometrics, and Informatics at Halle University Hospital and last author of the current study.

“Until now, there has been a lack of data on how frequently PAIS occurs in the general population following the COVID-19 pandemic, what symptoms are associated with it, and to what extent those affected seek medical care,” explains Jonas Frost, first author of the study and research associate at Halle University Hospital. The study team investigated these questions over the period from September 2024 to August 2025. Nearly 47,000 people reported on their experiences retrospectively.

“Our analysis shows that PAIS is a relatively common and clinically relevant phenomenon following respiratory tract infections and is not limited to a specific pathogen,” says Friederike Peter, co-first author of the study from the University Medical Center Halle, summarizing the results.

Just under half (48 percent of all respondents) reported having had at least one respiratory tract infection during the specified period. Younger people reported infections more frequently. About 4,300 people (19 percent of those with an infection) reported suffering from symptoms for at least twelve weeks afterward. The risk of long-lasting symptoms rose steadily with age: from 13 percent among those aged 20 to 29 to 21 percent among those aged 60 to 69.

A large proportion of those with persistent symptoms participated in a follow-up survey. This revealed that the symptoms were largely similar—regardless of the pathogen, which was known in one-quarter of the cases. Similar symptom patterns were observed particularly after COVID-19 and influenza infections. Most commonly, those affected reported that they had reduced physical stamina, became short of breath more quickly, were exhausted rapidly, and had less energy. Nearly 90 percent stated that the symptoms moderately to severely impaired their daily lives.

The duration of persistent symptoms was similar for COVID-19 and influenza infections. Within twelve months, about 17 percent of those with long-term illness had fully recovered. For the vast majority, the symptoms thus persisted for longer than a year. More than half (58 percent) of those potentially affected by PAIS sought medical help. Of these, 82 percent received medical treatment, though this was not specified in detail.

Since the data is based on the participants’ self-reports, it is subject to certain uncertainties. “Only infections that the respondents could recall were recorded. Severe cases were likely to have left a stronger impression. Furthermore, it is possible that people with long-lasting symptoms are more likely to remember a previous infection,” explains study author Peter.

The survey also only asked whether at least one respiratory infection had occurred during the period in question. Many people get infected several times a year. Furthermore, some of the information was reassessed later in the survey: a small proportion of the symptoms were not attributed to the infection by those affected. “Overall, we estimate a 16 percent risk of developing long-lasting symptoms that meet the criteria for PAIS following a respiratory infection within the period covered by the survey,” said study author Frost.

Background
The phenomenon known as “PAIS” has become particularly well-known due to the COVID-19 pandemic (SARS-CoV-2), specifically as “Long COVID.” However, such persistent symptoms following infections have been described for some time and do not occur exclusively after COVID-19 infections.

The current study is part of DigiHero, a population-based, Germany-wide study on digital health research. To date, more than 128,000 people across all federal states have registered. Participants are invited to take part in online surveys that include questions on the development of chronic diseases, healthy aging, and mental well-being, among other topics. Further information on the DigiHero study is available online at: www.umh.de/digihero

Recruitment for the DigiHero study was supported by internal funds and public grants. Funders include the Ministry of Economics, Science, and Digitalization of the State of Saxony-Anhalt, the German Center for Mental Health (DZPG, Halle-Jena-Magdeburg site), Jena University Hospital, the University of Münster, the Leibniz ScienceCampus Digital Public Health Bremen (LSC DiPH), the German Social Accident Insurance (DGUV), and the Faculty of Medicine at Charité – Universitätsmedizin Berlin.

Original publication
Frost J, Peter F, Glaser N, Frese T, Heuser M, Gekle M, Girndt M, Opel N, Behrens T, Karch A, Muellmann S, Zeeb H, Tüscher O, Mikolajczyk R: Post-infectious syndromes in the post-pandemic phase among the German general population. Dtsch Arztebl Int. September 18, 2026;123(19):arztebl.m2026.0134. doi: 10.3238/arztebl.m2026.0134.