Over a 13-year period, there was no significant increase in the odds of developing GBS within 6 weeks of receiving any vaccine (odds ratio 1.3, 95% CI 0.8-2.3), according to Roger Baxter, MD, of the Kaiser Permanente Vaccine Study Center in Oakland, Calif., and colleagues.
The findings from this retrospective study were consistent for the individual vaccines examined, including trivalent influenza vaccine (OR 1.1, 95% CI 0.4-3.1), the researchers reported online in Clinical Infectious Diseases.
“Although we had limited power to fully assess the risk of GBS following vaccination due the rarity of the outcome, the low numbers of GBS cases that were temporally associated with vaccination, coupled with our results, provide reassurance that the risk of GBS following any vaccine, including influenza vaccines, is extremely low,” they wrote.
GBS occurs at a rate of about one to two cases per 100,000 person-years around the world. Cases have been reported after administration of various vaccines, but causal connections are unclear.
A 1976 vaccination campaign for the H1N1 swine flu was halted after an increased risk of GBS became apparent, but most studies of seasonal flu vaccines since then have not demonstrated a similar relationship. A few have found a small increased risk of about one excess GBS case per million doses.
To further explore the potential risk of GBS after vaccination, the researchers analyzed data from patients who were hospitalized with GBS within the Kaiser Permanente Northern California system from 1994 through 2006. A neurologist confirmed the diagnoses through a review of medical records.
Through about 32.7 million person-years of follow-up, there were 415 incident cases of GBS covering Brighton levels 1, 2, and 3 identified. The average age of the patients was 48.5.
The researchers used a case-centered analysis, comparing the odds of vaccination within the 6- or 10-week period before the onset of GBS with the odds of vaccination during the same risk intervals for all vaccinated individuals in the health system population. The approach controls for the fact that more GBS cases were seen in the winter months.
Of the 415 GBS cases, only 25 were associated with vaccination in the 6 weeks before onset, most commonly with trivalent influenza vaccine (18 cases).
The odds of developing GBS were not increased in the 6 weeks following the use of any vaccine, including inactivated polio, tetanus, reduced diphtheria, and acellular pertussis (Tdap), 23-valent pneumococcal polysaccharide, injectable typhoid, hepatitis A, hepatitis B, combination tetanus and reduced diphtheria, or all of them combined.
Even if the five cases of GBS that occurred after flu vaccination and were not associated with a respiratory or gastrointestinal illness were considered to be caused by the vaccination, the upper limit of the 95% confidence interval would exclude a risk greater than one extra case of GBS per 585,000 doses.
Applying the same criteria to any non-influenza vaccination would exclude a risk greater than one extra case of GBS per 3.8 million doses.
Despite millions of doses delivered, there were no GBS cases observed in the 6 weeks following administration of any of the vaccines typically given to children, including oral polio, measles-mumps-rubella, conjugated pneumococcal, live-attenuated influenza, diphtheria-tetanus-acellular pertussis, varicella, Haemophilus-diphtheria-tetanus-pertussis, and Haemophilus B.
The authors acknowledged that the study could not exclude any possible association between vaccines and GBS and might have been limited by the fact that the reviewer of the medical records knew about the purpose of the study, and was able to see whether treating physicians considered GBS to be related to vaccination.
Source: MedPage TODAY