The Incidence of Guillain-Barré Syndrome during COVID-19 Pandemic: A Portuguese Multicentric Retrospective Study

Introduction: Guillain-Barré syndrome (GBS) is a rare peripheral nervous system inflammatory disease with an annual estimated incidence of 1-2/100 000. Several studies relate GBS with vaccination, especially against influenza. The literature is discordant on GBS incidence during the pandemic. Additionally, while vaccination is globally ongoing, GBS cases have been associated with an inoculation against SARS-CoV-2. Objective: To evaluate COVID-19 vaccination-associated Guillain-Barré syndrome cases and to establish their real incidence. Methods: Multicenter retrospective study with analysis of the GBS incidence and clinical characteristics in the pre-pandemic period (PPP), the pandemic pre-vaccination period (PPVP), and the pandemic vaccination period (PVP). Results: Forty-seven cases of GBS were identified: 13 in the PPP, 11 in the PPVP and 23 in the PVP. An increase in GBS cases (77%) was observed during the PVP when compared to the PPP, but it was not statistically significant (p = 0.10). Although an increase of the non-AIDP phenotype after vaccination period was observed (34.7%), a statistically significant relationship was not found. Conclusion: This study is the first Portuguese multicentric study regarding the incidence of GBS and SARS-CoV-2 infection and vaccination. We hypothesize that the slight decrease in GBS during the pandemic pre-vaccination period is probably due to hygienic measures implemented during the COVID-19 pandemic. Moreover, we found a small increase in the number of GBS cases with a possible relationship with COVID-19 vaccination. Prospective studies are necessary to better characterize this relationship and take further conclusions.