Impact of COVID-19 disease and COVID-19 vaccinations on hospital admissions for neurological diseases in the Lombardia over-12 population. Data from a self-controlled case series analysis.

Introduction: The influence of COVID19 vaccination on the risk of different neurological diseases has been subject of intense investigation. No large scale results have been published so far in the population of around 10 million people of Lombardia in Italy.

Methods: Linkable administrative health databases from the Lombardia region were used. By using the adapted self controlled case series (SCCS) method for event dependent exposures, we estimated the relative incidence of different neurological diseases following pre-specified windows at risk after vaccination and after COVID-19 infection in the over-12 population of Lombardia. Follow-up time before vaccination (Pre-Vax period) was compared with follow-up time 0-28 days (high-risk period) from the day of vaccination as well as for COVID infection. The SCCS model was fitted using a conditional Poisson regression model to estimate the relative incidences (RI) and their 95% Confidence Intervals (CI).

Results: The 28-day post-vaccination period was associated with a significant increase in the occurrence of ischemic stroke, cerebral haemorrhage, TIAs and myelitis (IRR 1.44, 1.50, 1.67 and 2.65 respectively). When the risk conferred by COVID19 infection was assessed in the same cohort, significant IRR were greater in the occurrence of ischemic stroke, cerebral haemorrhage, and TIAs (IRR 5.6, 3.62, 6.83) and includes also Multiple Sclerosis, neuromyelitis, and polymyositis (5.25, 8.81, 5.67).

Conclusions: Our data suggest that the increased risk of non-inflammatory CNS disorders following COVID-19 vaccination is lower than the risk conferred by COVID-19 infection, and that COVID-19 infection increases the risk of some inflammatory and non inflammatory neurological disorders.