Events temporarily associated with anti-influenza A (H1N1) vaccination in Mexico

In Mexico from December 2009 to June 2010, 45,490,501 doses of the vaccine against the influenza virus were administered; 27,048,330 of those corresponded to influenza A (H1N1) and 18,442,171 to seasonal influenza. Therefore, the assessment of events temporarily associated with vaccination (ETAV) is mandatory.

The database corresponding to the ETAV associated with influenza (A [H1N1] and seasonal) immunization reported between December 2009 and June 2010 was analyzed. Patients who displayed at least one ETAV with one of the following schedules were included: A) influenza A (H1N1) vaccine, B) seasonal influenza vaccine, C) influenza A (H1N1) vaccine and seasonal influenza vaccine.

A total of 597 ETAVs were reported. The 20- to 49-year-old age group was the most affected one (52.9%). The ETAV notification rate for influenza A (H1N1) vaccination was 1.41/100,000 applied doses vs. 0.74/100,000 applied doses corresponding to the seasonal influenza vaccination. Fifty seven events were considered serious (14 corresponded to Guillain-Barré syndrome) and these were considered coincidental unrelated events.

There is no evidence of an increased rate of Guillain-Barré Syndrome with respect to the cases expected in the general population.