‘Flaws’ in Previous Studies?
The findings in hospitalized patients were in line with previous findings, but those in nonhospitalized patients stand out, they added.
Previous studies were done predominantly in older males with comorbidities and those who were more socioeconomically disadvantaged, which could lead to a bias, Dr. Hviid said.
Those other studies “had a number of fundamental flaws that we do not believe our study has,” Dr. Hviid said. “Our study was conducted in the general population, with free and universal testing and healthcare.”
Researchers stress that sequelae after infection are predominantly associated with severe illness.
“Today, a healthy vaccinated adult having an asymptomatic or mild bout of COVID-19 with the current variants shouldn’t fear developing serious psychiatric or neurologic disorders in the months or years after infection.”
One limitation is that only hospital contacts were included, omitting possible diagnoses given outside hospital settings.
‘Extreme Caution’ Required
The link between COVID-19 and brain health is “complex,” and the new findings should be viewed cautiously, said Maxime Taquet, MRCPsych, PhD, National Institute for Health and Care Research clinical lecturer and specialty registrar in Psychiatry, Oxford Health NHS Foundation Trust, England, who commented on the findings.
Previous research by Dr. Taquet, who was not involved in the current study, found an increased risk for neurologic and psychiatric diagnoses during the first 6 months after COVID-19 diagnosis.
The current study “contributes to better understanding this link by providing data from another country with a different organization of healthcare provision than the US, where most of the existing data come from,” Dr. Taquet said.
However, “some observations — for example, that COVID-19 is associated with a 50% reduction in the risk of autism, a condition present from very early in life — call for extreme caution in the interpretation of the findings, as they suggest that residual bias has not been accounted for,” Dr. Taquet continued.
Authors of an accompanying editorial, Eric Chow, MD, MS, MPH, of the Division of Allergy and Infectious Diseases, University of Washington, School of Public Health, and Anita Chopra, MD, of the post-COVID Clinic, University of Washington, Seattle, called the study a “critical contribution to the published literature.”
The association of neurologic and psychiatric diagnoses with severe disease “is a reminder of the importance of risk reduction by combining vaccinations with improved indoor ventilation and masking,” they concluded.
The study was supported by a grant from the Independent Research Fund Denmark. Dr. Hviid and coauthors, Dr. Chopra, and Dr. Taquet reported no relevant financial relationships. Dr. Chow received a travel award from the Infectious Diseases Society of America to attend ID Week 2022.
A version of this article appeared on Medscape.com.