Influenza Linked to Increased Risk of Parkinson’s Disease

Influenza A viruses infect a number of different species, ranging from birds to mammals including humans. In addition to the welldefined respiratory effects, acute influenza infection in humans can lead to the development of a number of encephalitic syndromes, each having neurological consequences. This can happen with other respiratory viruses also.

A new study published in the journal JAMA Neurology evaluated whether prior influenza and other infections are associated with Parkinson’s disease more than 10 years after infection. The case-control study used data from 1977 to 2016 from the Danish National Patient Registry. All the individuals with Parkinson disease where included and matcher to 5 population controls on sex, age and date of diagnosis. 

The study included a total of 61,626 (38.4%), of which 23,828 were female and 53,202 (86.3%) were older than 60 years. A total of 10 271 individuals with Parkinson disease and 51 355 controls were identified. Influenza diagnosed at any time during a calendar year was associated with Parkinson disease more than 10 years later. 

The researchers found that influenza was associated with diagnoses of Parkinson’s disease more than 10 years after the infection. Their observational study suggests a link between influenza and Parkinson disease but does not demonstrate causality. 

Previous studies on seasonal and pandemic flu have indicated that the viral infections can cause symptoms similar to Parkinson’s in the short term. Infections can trigger inflammation and even injury in regions of the brain such as the substantia nigra that are affected by neurodegenerative disease. However, there has been no data indicating that a case of the flu directly increases one’s risk of developing Parkinson’s years or decades later. The new study credibly indicates that there is a relationship between the flu and Parkinson’s disease that ought to be further probed in subsequent research.

Study coauthor Noelle Cocoros told The Scientist: “There is some compelling evidence for a viral connection to Parkinson’s.”

Cocoros and coauthor Victor Henderson, a neurologist and epidemiologist at Stanford University, acknowledge that drawing conclusions from historical health records will always result in imperfect answers, but they argue that large health record databases like Denmark’s are the best tools available to conduct research over such a long period of time. Further research needs to be conducted in order to draw conclusions, but the results provide us some insight into factors that might influence the development of this condition. 


Noelle M. Cocoros, et al. Long-term Risk of Parkinson Disease Following Influenza and Other Infections. JAMA Neurol. Published online October 25, 2021. doi:10.1001/jamaneurol.2021.3895

Dan Robitzki (2021, Nov 19). Study Links Flu to Increased Parkinson’s Risk a Decade Later. The Scientist. Retrieved from:

Shankar Sadasivan, et al. Synergistic effects of influenza and 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) can be eliminated by the use of influenza therapeutics: experimental evidence for the multi hit hypothesis. npj Parkinson’s Disease (2017)3:18; doi:10.1038/s41531-017-0019-z 

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