Guillain Barré syndrome (GBS) is commonly feared with vaccines and of particular concern as new technologies such as mRNA-based or adenovirus-vectored COVID-19 vaccines have emerged.

Data from VigiBase, an international adverse drug reaction database, evidenced a lower reporting rate of GBS associated with mRNA-based COVID-19 vaccines compared with adenovirus-vectored COVID-19 vaccines, as the observed-to-expected ratio was consistently < 1.0 for mRNA-based COVID-19 vaccines and > 2.0 for adenovirus-vectored COVID-19 vaccines.

These results suggesting no safety concern for GBS with mRNA-based COVID-19 vaccines and an increased risk with adenovirus-vectored COVID-19 vaccines were in accordance with other data, and suggested spontaneous reporting may be convenient to quantify risks during a vaccination campaign.