Mar 222011

Vaccine safety is one of the major areas of  concern of the anti-vaccination crowd.  Guillan-Barre syndrome is a subset of said concern; it is feared that some vaccines might increase the incidence rate. It appears the science-based evidence is a bit unclear on the issue. Luckily this is being followed closely by scientists all over the world. One such group of scientists recently published a study in the New England Journal of Medicine which addresses the concern.

Safety of Influenza A (H1N1) Vaccine in Postmarketing Surveillance in China

Xiao-Feng Liang, M.D., Li Li, M.D., Ph.D., Da-Wei Liu, M.D., Ke-Li Li, M.D.,Wen-Di Wu, M.D., Bao-Ping Zhu, M.D., Hua-Qing Wang, M.D., Ph.D.,Hui-Ming Luo, M.D., Ling-Sheng Cao, M.D., Jing-Shan Zheng, M.D.,Da-Peng Yin, M.D., Lei Cao, M.P.H., Bing-Bing Wu, M.D., Hong-Hong Bao, M.D.,Di-Sha Xu, M.D., Wei-Zhong Yang, M.D., and Yu Wang, M.D., Ph.D.

Summary -On September 21, 2009, China began administering vaccines, obtained from 10 different Chinese manufacturers, against 2009 swine flu pandemic. Prior to the start of the 2009 H1N1 vaccination drive, authorities instituted a surveillance system to monitor the vaccines’ safety. Physicians or vaccination providers were required to report the numbers of vaccinees and all adverse events to their local Center for Disease Control and Prevention; data was collected for 6 months, through March 21, 2010.

A total of 89.6 million doses of vaccine was administered during the 6 months. One of the variables analyzed was Guillan-Barre syndrome rates, given that the 1976-77 US swine flu vaccine was associated with increased incidence of Guillan-Barre. Furthermore, since serious adverse vaccine reactions such as the Guillain–Barre syndrome are extremely rare, the usual clinical trials are not big enough to detect their occurrence. Therefore, post-marketing surveillance for  such adverse events after immunization is required to evaluate the safety of the swine flu vaccine. That is exactly what this study aimed to do.

Results – Of the 90 million doses of vaccines administered, the reported adverse effects break down as follows:

  • 8,067 total reported
    • 6,552 verified as vaccine related
      • 5,469 common minor reactions
      • 1,050 allergic reactions
      • 33 serious reactions, of which 29 had neurologic reactions including 8 cases of Guillan-Barre
    • 1,064 coincidental illness
    • 409 psychogenic reactions
    • 42 unclassifiable
  • 10 deaths occurred within 9 days of vaccination (5 males, 5 females)
    • 9 had preexisting condition
    • 1 had no prior history of medical issues
  • 11 total cases of Guillan-Barre syndrome reported
    • 8 no evidence of other cause besides vaccination
    • 1 coincidental
    • 2 unclassifiable
    • 3 of the 11 were in children under 15 years of age for a rate of 0.1/million vaccinated

Conclusion -The study has some limitations:

  1. The majority of the people vaccinated included higher proportions of students, teachers, and health care providers than the proportions in the general population. These groups tend to be healthier and have greater access to health care.
  2. The vaccine is brand new which could lead participants to over-report adverse effects soon after vaccination.
  3. Reporting of non-serious reactions such as low-grade fever or mild local reactions was not mandatory; therefore, the rate was most likely under-reported.
  4. The study relied on reporting from participants to the doctors, and then from doctors to the Chinese CDC, which could lead to under-reporting. In fact the authors noted that rates of reporting were higher from the more economically well to do areas than the less economically well to do ones. On the other hand, such under-reporting is most likely to happen with non-serious events, as opposed to the more serious events such as Guillan-Barre (it is easier for a doctor to forget to report a few cases of elevated fever, vs. the one case of Guillan-Barre she may come across.)

Keeping these limitations in mind, this study had an extremely large sample of close to 90 million doses of vaccines administered, thus it was sensitive enough to pick up on very rare vaccine side effects, such as Guillan-Barre which numbers in a few cases in the millions, and thus cannot be expected to be picked up by even the largest clinical trials which at best enroll thousands of participants. This study showed that:

  • In children under 15 years of age, the rate of Guillan-Barre syndrome associated to vaccines was 0.1/million .much less than background rate of 1.9/million during the same period (which in turn was lower than the rate for the same period the prior year)
  • Overall rates of Guillan-Barre, in all age groups, did not exceed the baseline rate in European countries (0.6-1.9 per million)
  • The rate also does not exceed the estimated 1 case/million in the United States

Overall, this study failed to find any evidence that the swine flu vaccine was associated with any increase in Guillan-Barre syndrome rates either in the children under 15 population, or the population as a whole. In fact it found rates that were lower than European or US estimated rates associated with influenza vaccines.

In layman’s terms: this study suggest that taking the swine flu vaccine does not increase one’s lifelong chances of developing Guillan-Barre syndrome.

The author’s concluded as such:

In conclusion, these findings suggest that the H1N1 vaccine has a reasonable safety profile, and there is no evidence that the vaccine is associated with an increased risk of the Guillain–Barré syndrome.

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