Protocol on estimation of Guillain-Barré syndrome background rates in general population in low- and middle-income countries

Overview

Background rates of possible adverse events are crucial to monitoring vaccine safety as they help separate potential safety signals following vaccination from events that are temporally associated with but not caused by vaccination. The association between Guillain-Barré syndrome (GBS) and vaccination is of interest in vaccine safety studies because GBS has been identified as a rare adverse event of special interest (AESI) associated with certain vaccine products.

GBS is a rare acute peripheral neuropathy manifested principally as muscle weakness and loss of reflexes. The underlying etiology and pathophysiology of GBS are not entirely understood, but immune stimulation is believed to play a role in its pathogenesis. Two thirds of GBS cases are preceded by a respiratory or gastrointestinal infection but GBS after vaccination has also been observed, although rarely.

A potential association between GBS and vaccination (seasonal influenza vaccines, H1N1 vaccine, human papillomavirus vaccine, hepatitis B vaccine, recombinant zoster vaccine, coronavirus disease 2019 [COVID-19] vaccine) has been debated extensively. For influenza vaccines, a small but statistically significant association has been reported, particularly for pandemic vaccines.

Although the current consensus is that, in most situations, the benefits of vaccination outweigh the risks of GBS, reported associations of GBS with the 1976 swine flu vaccine, as well as the quadrivalent meningococcal conjugate vaccine demonstrate that some safety concerns still exist. More research is needed to better understand this association and whether a causal link exists between GBS and vaccination against viral or bacterial infections.

Establishing GBS background rates before the introduction of new vaccines (for example, new influenza vaccines) will be instrumental for evaluating the occurrence of adverse events following vaccine introduction.

An improved understanding of between-country variation in GBS background rates will be assisted by measuring GBS incidence rates following recent viral or bacterial infection and following receipt of a vaccine product.