Covid can end as an emergency and still leave a mark on ordinary working life. In Denmark, people who had the infection were more likely to spend a substantial stretch of time away from work afterward. As societies adjusted to living with Covid, research shifted from emergency questions toward the health and economic burden left behind.

But measuring that burden is difficult: symptoms vary, and it can be hard to separate effects after infection from health problems that were already there. It also remained unclear how these after-effects changed daily life and quality of life, and which groups faced the greatest risk of prolonged illness.

So the study focused on a practical question: was Covid infection linked with sick leave after the initial illness? The comparison was between people infected during two pandemic periods in Denmark and people with no known history of infection. Researchers compared people infected with SARS-CoV-2 with people who had no known history of infection, then examined post-acute sick leave following infection in Denmark.

To make that comparison, the study merged nationwide survey and register data. In Denmark, a unique identifier lets records from different sources be linked for the same person. The survey and register information together described the study population and the measures used in the analysis.

Substantial sick leave meant one full month of sick leave during the eight-month period beginning one month after the test. The same kind of outcome was defined for part-time sick leave. The central finding was an additional 33 people per 1000 taking substantial sick leave after infection, compared with people with no known history of infection.

The risk was higher for women, people aged 50 to 65, and people with conditions including obesity, chronic lung disease, and fibromyalgia. The difference was clear: substantial sick leave affected 1.4 percent of people who tested negative, compared with 4.5 percent of people who tested positive.

Among people who tested negative, the level was similar across age groups. Among people who tested positive, substantial sick leave increased with age. Only 21.1 percent of the infected people who took substantial sick leave had a hospital-registered diagnosis for lasting effects of the infection.

The age pattern is visible at a glance: lasting absence from work rises steadily with age after infection, while it stays broadly level among those who tested negative. The extra amount of sick leave was greater for women than for men, and it was higher for people aged 50 to 65 and for nearly all the health conditions examined.

The largest differences appeared among people with fibromyalgia, chronic lung disease, and diabetes. Obesity also showed a larger difference than in the general population. Healthcare workers also had a larger difference than the general population.

There is an important limit: the sick leave was self-reported, so participation and memory may have affected the results. The questionnaire asked about sick leave in general, so its duration could not be directly attributed to lasting Covid symptoms. Register records would miss many shorter absences, making them less suited to capturing illness that comes and goes.

The study links Covid infection with more than a month of sick leave in the following months, especially among older adults, women, and people with certain health conditions. That makes lost working time one visible measure of the illness’s wider cost.