Google Trends reveals a Temporal Correlation between A(H1N1) 2009 Influenza vaccination and Guillain-Barré Syndrome

Despite great concern prompted by memories of the 1976 influenza A(H1N1) outbreak and the United States mass vaccination program, which was stopped because of the emergence of increasing cases of Guillain-Barré syndrome (GBS) among vaccine recipients, a correlation between A(H1N1) 2009 influenza and an increased incidence of GBS is still matter of debate. This study aimed to interpret changes over time of web search queries for terms related to influenza and influenza vaccination and GBS in English-speaking countries in 2009, to evaluate a possible association between H1N1 vaccination and increased GBS incidence. Using Google Trends (available at: http://www.google.com/trends, accessed January 10, 2025), data on global search queries for terms related to GBS and influenza vaccine between January 2009 and December 2009 were analyzed. The autumnal peak for the term “Guillain-Barré” (8-14 Novembre 2009) followed of one-two week(s) that for terms related to influenza vaccination (25-31 October 2009). The increased search volumes for GBS occurred exactly one to two weeks after the peak of search terms related to influenza vaccination supports the hypothesis of a strict temporal correlation between them. Further studies are warranted to evaluate whether this temporal correlation is spurious or not.