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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

Questions & Answers

2009 H1N1 Flu In The News

November 24, 2009 6:00 PM ET

2009 H1N1 Influenza Vaccination Safety

How many adverse event reports among people who received 2009 H1N1 vaccine have been reported to CDC?
As of November 20, 2009, the CDC Vaccine Adverse Event Reporting System (VAERS) had received 3,182 adverse event reports following 2009 monovalent H1N1 vaccination. The vast majority (94%) of adverse events reported to VAERS after receiving the 2009 monovalent H1N1 vaccine have not been serious (e.g., they encompass things like soreness at the vaccine injection site). CDC and FDA will be providing weekly updates on our vaccine safety monitoring activities in an effort to better characterize data that are being viewed publicly through the Vaccine Adverse Event Reporting System (VAERS) and CDC’s website, WONDER

How does 2009 H1N1 vaccine safety compare to seasonal flu vaccine safety?
The number of serious health events reported after H1N1 vaccination is very similar to the number of reports that typically follow seasonal influenza vaccines. Additionally, no new or unusual events or pattern of adverse events have emerged.

How many Guillain-Barré syndrome (GBS) cases have been reported after 2009 H1N1 vaccination?
We know there has been interest in Guillain-Barré syndrome (GBS). CDC employs three vaccine monitoring systems that will alert us quickly should any indications of GBS-related issues arise, including: Vaccine Adverse Event Reporting System (VAERS), Vaccine Safety Datalink (VSD), and a collaboration in 10 states to look actively look for cases of GBS regardless of vaccination. To date, there are no indications of GBS-related problems with the 2009 H1N1 vaccine. It is important to note that each week in the United States, about 80-160 cases of GBS occur in the general population - regardless of vaccination. For more information about GBS: Fact Sheet: Guillain-Barré Syndrome (GBS).

How is the government monitoring H1N1 vaccine safety?
The Federal government has a robust vaccine safety monitoring program that has been enhanced further to ensure 2009 H1N1 vaccine safety. Details available at Federal Plans to Monitor Immunization Safety for the Pandemic 2009 H1N1 Influenza Vaccination Program.

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