Narcolepsy is a chronic sleep disorder that affects approximately 1 in 2,000 individuals. It is characterized by excessive daytime sleepiness, sudden loss of muscle tone, and vivid hallucinations. In 2009, during the H1N1 pandemic, there was a significant increase in the incidence of narcolepsy in some countries, including China. A new study from China suggests that the increase in narcolepsy cases during the pandemic period was not linked to the Pandemrix vaccine, which was originally suspected as the cause of the surge in narcolepsy diagnoses. Read on to learn more about the findings of this important study.
The incidence of narcolepsy increased threefold in China during the 2009 H1N1 pandemic, according to a study led by Xiling Wang, PhD, School of Public Health, Fudan University. An examination of data from 1990 to 2017 found that the average annual incidence was 0.79 per 100,000 person-years (PY) from 1990 to 2017 and 1.08 per 100,000 PY from 2003 to 2017 in mainland China, with the highest incidence observed in 2010 at 3.74 per 100,000 PY. The study also found that the incidence of narcolepsy before, during, and after the pandemic was 0.83 (95% CI, 0.82-0.83), 3.07 (95% CI, 3.04-3.10), and 1.02 (95% CI, 1.01-1.02) per 100,000 PY, respectively. Results demonstrated that the increased risk was statistically significant during and post-pandemic compared to the pre-pandemic period, and was robust to sensitivity analysis for narcolepsy type 1 (NT1) cases or after excluding the effect of the H1N1 pandemic vaccine, Pandemrix.
The study, which examined epidemiological data collected from a Chinese population, enrolled 2869 eligible patients with narcolepsy. Age group and sex were adjusted on a Poisson regression model to find a statistically significant increase in incidence of narcolepsy during and post-pandemic as compared to the pre-pandemic period (incidence rate ratio [IRR], 4.17 [95% CI, 4.12-4.22]; IRR, 1.42 [95% CI, 1.41-1.44). For patients with onset during the pandemic, the number of sleep-onset rapid eye movement period (SOREMP) was higher than that of other patients (P <.001). There was a significant increase in the proportion of NT1 among patients with narcolepsy during and after the pandemic (P <.001).
The study confirmed a previous assumption of the autoimmune nature of narcolepsy type 1, but direct evidence is lacking. Rolf Fronczek, MD, neurologist, Leiden University Medical Center, and colleagues stated in a related editorial that “more than 20 years after the discovery of hypocretin deficiency in narcolepsy with cataplexy the ultimate question remains unsolved. What happens to the hypothalamic hypocretin neurons in narcolepsy type 1? Are the hypocretin neurons of genetically susceptible people indeed irrecoverably killed by T-cells that wrongly elicit an immune response to a self-antigen in hypocretin neurons after an immune trigger (or several triggers)? Or is the immune mechanism in reality aimed at another target outside hypocretin neurons? Are the hypocretin neurons really gone?”
In conclusion, the link between the H1N1 pandemic and an increase in narcolepsy incidence has long been a topic of discussion and research. However, this recent Chinese report suggests that the Pandemrix vaccine was not the driving factor for this increase. It is important to continue studying and understanding the causes of narcolepsy to better diagnose and treat those who may be suffering from this debilitating disorder. As always, consulting with a medical professional and staying up to date on the latest research findings is crucial for those impacted by narcolepsy or any other health condition.
