The most common were loss of taste and smell, muscle pain and general fatigue.

- This is a completely unique study in which we can now better than ever before estimate the percentage of people who suffer from long-term symptoms after covid-19, says the study's first author, PhD student Aranka Ballering at the University of Groningen, to Dagens Nyheter.

Her assessment is based on the fact that the researchers used a special method to assess how many had problems due to the infection and not for any other reason.

23 different symptoms

The study is based on a digital questionnaire that roughly 76,000 answered during the period March 2020 to August 2021. This allowed them to see how the people's state of health changed and follow how widespread 23 different symptoms were.

The questions were asked on 24 occasions.

It turned out that 21.4 percent of the people who were infected had at least one of the symptoms for three to six months after they were diagnosed with Covid-19 or tested positive for SARS-Cov2.

In the control group without confirmed infection, 8.7 percent had at least one of these symptoms.

The researchers therefore conclude that the difference of 12.7 percent is explained by the previous infection.

Around 30,000 in Sweden

Previous studies on long-term covid have come up with very variable results, from a few tenths of a percent to just over 70 percent, writes Dagens Nyheter.

In Sweden, around 30,000 people have been diagnosed with post-covid or post-infectious condition after covid-19.

The Dutch study is published in the medical journal The Lancet.