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H1N1 (Swine Flu): Vaccine Safety – Report of Adverse Reactions in the U.S. October 1–November 24, 2009

There has been lots of discussion about the pandemic H1N1 vaccine amongst the protagonists and the antagonists alike.  The protagonists believe the vaccine is safe and we must have it in order to stop the spread of the disease and the antagonist believe it is unsafe and will cause wide spread death and suffering and is part of the Big Pharma response.  Wow – not much middle ground there!

MMWR Report

CDC has just issued the MMWR that details the first reports on vaccine safety in the U.S.  The FDA licensed the first 2009 pandemic vaccine (H1N1 monovalent vaccine or “H1N1 vaccines” on September 15, 2009.

  • None of these vaccines contains an adjuvant.
  • The licensure and manufacturing processes for the vaccine were the same as those used for seasonal flu.

The H1N1 vaccines are available as a:

  • Live, attenuated monovalent vaccine (LAMV) for intranasal administration
  • Monovalent, inactivated, split-virus or subunit vaccines for injection (MIV)

Vaccine Adverse Event Reporting System (VAERS)

To assess the safety profile of H1N1 vaccines in the United States, CDC reviewed vaccine safety results for the H1N1 vaccines from

  • 3,783 reports received through the U.S. Vaccine Adverse Event Reporting System (VAERS)
  • Electronic data from 438,376 persons vaccinated in managed-care organizations in the Vaccine Safety Datalink (VSD), a large, population-based database with administrative and diagnostic data, in the first 2 months of reporting (as of November 24).
vaccine vares
VAERS data indicated 82 adverse event reports per 1 million H1N1 vaccine doses distributed, compared with 47 reports per 1 million seasonal influenza vaccine doses distributed.
  • No substantial differences between H1N1 and seasonal influenza vaccines were noted in the proportion or types of serious adverse events reported.
  • No increase in any adverse events under surveillance has been seen in VSD data.

Many agencies are using multiple systems to monitor H1N1 vaccine safety. Health-care providers and the public are encouraged to report adverse health events that occur after vaccination.

Reports to VAERS

VAERS enables early detection of potential new, rare, or unusual patterns of adverse events, which then can be investigated using other methods and systems to determine whether an actual association with vaccination exists. What are the reporting requirements?

  • Health-care providers and manufacturers are required to report to VAERS certain adverse events in vaccinees brought to their attention after vaccination with licensed U.S. vaccines.
  • Health-care providers and members of the public may also report other adverse events voluntarily.

There were several changes made to VAERS to enhance reporting with the initiation of the H1N1 vaccination program.  This included providing VAERS contact information on influenza vaccination record cards, advertising in medical journals, utilizing state vaccine safety coordinators, and increasing the number of staff members who code reports and obtain and review medical records,

CDC and FDA staff members review all VAERS data. Reporting rates were calculated per 1 million doses distributed as of November 20.  Through November 24, VAERS received:

  • 3,783 reports of adverse events after receipt of H1N1 vaccine 204 were categorized as serious
  • 4,672 reports after receipt of seasonal influenza vaccines, of which 283 were serious

Vaccine data from October 5 – November 20 revealed the following:

  • H1N1 Vaccine a total of 46.2 million doses (11.3 million LAMV and 34.9 million MIV doses)
    • Overall VAERS adverse event reporting rates were 82 per 1 million H1N1 vaccine doses distributed
    • The serious adverse event reporting rates were 4.4 serious adverse events per 1 million doses distributed.
  • Seasonal Flu: 98.9 million doses
    • Overall VAERS adverse event reporting rates were 47 per 1 million seasonal influenza vaccine doses distributed.
    • The serious adverse event reporting rates were 2.9 serious adverse events per 1 million doses distributed.
vaccine shot 470 0909
However, the percentage of serious adverse events among all adverse events reported after receipt of seasonal influenza vaccines was slightly higher (6.1%), compared with the percentage of serious adverse events after receipt of H1N1 vaccines (5.4%), and this finding was consistent for inactivated (5.8% versus 5.5%) and live attenuated (7.3% versus 4.7%) vaccines.

Vaccine Deaths

  • VAERS received 13 reports of deaths occurring after receipt of H1N1 vaccine
    • Three deaths occurred after receipt of LAMV
    • 10 after receipt of MIV.
    • In nine of these deaths, significant underlying illness (including illness that might be indication for vaccination) was present
    • One death resulted from a motor vehicle crash
    • The remaining three deaths await review of final autopsy results or death certificates by CDC

Guillain-Barré Syndrome

  • VAERS had received 10 reports of Guillain-Barré syndrome
  • Two additional reports of possible Guillain-Barré syndrome were identified by medical officers reviewing other reports to VAERS describing neurologic events.
  • After chart review, four of these 12 reports (all after receipt of MIV) met Brighton Collaboration criteria for Guillain-Barré syndrome, four did not meet the criteria, and four are under review.


  • VAERS also received 11 reports of anaphylaxis
  • Additional eight reports of possible anaphylaxis were identified by medical officers reviewing reports to VAERS of serious allergic events.
  • Of these 19 cases, 13 met Brighton Collaboration criteria, five had an anaphylaxis diagnosis on medical record review, and one has not been confirmed.
  • Three of the Guillain-Barré syndrome cases and 15 of the anaphylaxis cases were coded as serious adverse events, in accordance with federal regulation.

The remaining 173 nonfatal serious adverse events after vaccination with H1N1 vaccines are under chart review. These reports fall into the following diagnostic categories: neurologic or muscular condition other than Guillain-Barré syndrome (49 [28%]); pneumonia or influenza-like illness (27 [16%]); other noninfectious conditions, including multiple medical symptoms (19 [11%]); respiratory or ear, nose, and throat condition (17 [10%]); allergic conditions other than anaphylaxis (16 [9%]); pregnancy complications** (15 [9%]); other infectious symptoms (10 [6%]); gastrointestinal (eight [5%]); cardiovascular (six [3%]); and psychiatric (six [3%]). Each category includes a variety of diagnoses; no patterns were identified.

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