COVID-19 vaccination did not deteriorate physical, mental, or cognitive health

Vaccinated Danes did not report poorer physical, mental, or cognitive health in the months following vaccination in comparison to the unvaccinated, concluded a large survey study on COVID-19 vaccine safety in the Danish population.

Researchers from Statens Serum Institut (SSI) investigated the associations between COVID-19 vaccination status and several physical, mental, and cognitive symptoms. The researchers explored a variety of symptoms, ranging from headache, dizziness, and fatigue, to anxiety, depression, and difficulty concentrating.

A survey with 36,436 participants

The large survey was based on 36,436 Danish residents who each filled out two questionnaires: one about their general health and lifestyle characteristics, and one about experienced symptoms. The researchers linked this survey data to COVID-19 vaccination status from the Danish vaccination register and were able to examine how many participants reported each symptom among the vaccinated and unvaccinated, respectively.

Reassuring results

The results were reassuring. Overall, the researchers did not find any signs of deteriorating physical, mental, or cognitive health several months after vaccination.

“Our study is quite unique. It is one of the first studies at all to investigate whether there is a connection between COVID-19 vaccination and physical, mental, and cognitive symptoms. It is also quite big with more than 36,000 participants. It was reassuring to see that our study paints a picture of a safe vaccine,” explained Professor Anders Hviid from SSI, who spearheaded the study.

Fatigue was more prevalent among the unvaccinated

Some of the symptoms reported more frequently in the survey were physical and mental exhaustion and cognitive difficulties. Physical exhaustion was reported by 27.4% of the vaccinated and 29.8% of the unvaccinated. For mental exhaustion, these figures were 30.5% and 32.1%, and for cognitive difficulties, 31.9% and 33.2%. Thus, there were no significant differences between the groups. Some of the only symptoms which differed between the vaccinated and unvaccinated were fatigue and post-exertional malaise, which unvaccinated individuals reported more frequently. Fatigue was reported by 37.5% of the unvaccinated but only by 28.7% of the vaccinated. The corresponding figures for post-exertional malaise were 24.2% and 15.5%.

“Vaccines protect against COVID-19, which might be a possible explanation for why the unvaccinated experienced more fatigue. None of the participants in the survey tested positive for COVID-19, but there could be some infections that slipped through the test system, especially while the Omicron was at its highest,” said Anders Hviid.

The study, which has not yet been peer-reviewed, was recently published as a pre-print on the SSRN service.

Read more

Read the preprint article here (opens in a new window)

Press contacts
Contact Statens Serum Institut’s press department at telephone number +45 2260 1123 or e-mail

Press contacts

Contact Statens Serum Institut’s press department at telephone number +45 2260 1123 or e-mail