INFLUENZA PANDEMIC (H1N1) (37): GUILLAIN-BARRE SYNDROME RISK (US)

[Wishart, Michael]

INFLUENZA PANDEMIC (H1N1) (37): GUILLAIN-BARRE SYNDROME RISK
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A ProMED-mail post

ProMED-mail is a program of the
International Society for Infectious Diseases

Preliminary Results: Surveillance for Guillain-Barre Syndrome After
Receipt of Influenza A (H1N1) 2009 Monovalent Vaccine — United
States, 2009–2010
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Guillain-Barre syndrome (GBS) is an uncommon peripheral neuropathy
causing paralysis and in severe cases respiratory failure and death.
GBS often follows an antecedent gastrointestinal or upper respiratory
illness but, in rare cases, can follow vaccination. In 1976,
vaccination against a novel swine-origin influenza A (H1N1) virus was
associated with a statistically significant increased risk for GBS in
the 42 days after vaccination (approximately 10 excess cases per one
million vaccinations), a consideration in halting the vaccination
program in the context of limited influenza virus transmission. To
monitor influenza A (H1N1) 2009 monovalent vaccine safety, several
federal surveillance systems, including CDC’s Emerging Infections
Program (EIP), are being used. In October 2009, EIP began active
surveillance to assess the risk for GBS after 2009 H1N1 vaccination.
Preliminary results from an analysis in EIP comparing GBS patients
hospitalized through 31 Mar 2010 who did and did not receive 2009 H1N1
vaccination showed an estimated age-adjusted rate ratio of 1.77 (GBS
incidence of 1.92 per 100 000 person-years among vaccinated persons and
1.21 per 100 000 person-years among unvaccinated persons). If
end-of-surveillance analysis confirms this finding, this would
correspond to 0.8 excess cases of GBS per one million vaccinations,
similar to that found in seasonal influenza vaccines. No other federal
system to date has detected a statistically significant association
between GBS and 2009 H1N1 vaccination.
Surveillance and further analyses are ongoing. The 2009 H1N1 vaccine
safety profile is similar to that for seasonal influenza vaccines,
which have an excellent safety record. Vaccination remains the most
effective method to prevent serious illness and death from 2009 H1N1
influenza infection; illness from the 2009 H1N1 influenza virus has
been associated with a hospitalization rate of 222 per one million and
a death rate of 9.7 per one million population.

[Readers should access the original text at the above URL for
descriptions of the organisation of the survey, the methodology and
literature references. – Mod.CP]

MMWR Editorial Note:

This preliminary analysis showed an elevated, statistically
significant association between 2009 H1N1 vaccination and GBS. If
confirmed, the excess risk for GBS associated with 2009 H1N1 vaccine
of 0.8 cases per one million vaccinations would be comparable to the
excess described previously for some trivalent seasonal influenza
vaccine formulations (approximately one excess case per one million
vaccinations), and much smaller than the risk for GBS observed during
the 1976 swine influenza vaccine campaign (approximately 10 excess
cases per one million vaccinations).

Notably, the high proportion of antecedent illnesses associated with
GBS (e.g., gastrointestinal illness or respiratory infection) suggest
that a number of the GBS illnesses observed after vaccination might be
attributable to other antecedent illness; historically, 40-70 percent
of GBS patients report experiencing an antecedent infectious illness.
Also, data demonstrating an association between GBS and the 1976 swine
flu vaccines described a clustering of cases during the 2nd and 3rd
weeks following vaccination.

Similarly, a single study of seasonal influenza vaccine and GBS risk
using combined data from 1992/1993 and 1993/1994 seasonal influenza
vaccine formulations showed GBS cases peaked at 2 weeks following
vaccination, whereas the EIP data did not demonstrate this same
clustering effect for the 2009 H1N1 vaccine.

Safety monitoring is an integral part of any vaccination program. The
federal government is using several other systems to monitor 2009 H1N1
vaccine safety, including programs to detect potential associations
between GBS and the vaccine. These systems differ in the size of the
population under surveillance, methods to identify and verify GBS
cases, and methods to determine the vaccine status of persons with and
without GBS. Interpreted collectively, these systems provide a
comprehensive picture of vaccine safety. Preliminary safety data from
VAERS (Vaccine Adverse Event Reporting System) indicate that the
safety profile of 2009 H1N1 vaccines is similar to the profile for
seasonal influenza vaccines, which have an excellent safety record.

To date, VSD (Vaccine Safety Datalink), PRISM (Post-Licensure Rapid
Immunization Safety Monitoring), DoD/DMSS (Department of
Defense/Defense Medical Surveillance System), VA (Department of
Veteran Affairs), CMS (Centers for Medicaid and Medicare Services),
and CDC’s EIP have found a non-significant but slightly elevated
relative risk (C. Vellozzi, CDC, personal communication, 2010).

The findings in this preliminary report are subject to at least 5
limitations. 1st, misclassification of some cases might have occurred,
particularly in younger patients where the diagnosis of GBS can be
difficult, which might result in an underestimate of GBS cases;
however, such an underestimate could bias the rate ratio in either
direction. 2nd, some inaccurate reporting of the date of vaccination
might have occurred, potentially resulting in an overestimate or
underestimate of cases within the risk window. 3rd, the rate ratio
relies on vaccination coverage estimates using BFRSS (Behavioral Risk
Factor Surveillance System) and NHFS (National 2009 H1N1 Flu
[telephone] Survey data; based on work from previous seasons studying
seasonal influenza vaccine, 2009 H1N1 vaccination coverage estimates
might be overestimated by as much as 2 or 3 percentage points, which
might produce an underestimate of the rate ratio. 4th, incomplete case
ascertainment or reporting bias might have occurred. However, these
likely would have had a minimal effect because active case finding was
conducted throughout the surveillance period.

****Finally, none of the vaccine monitoring systems currently in use,
including EIP, can fully account for other confounding risk factors
for GBS that might not be measured or accounted for but might be
associated with vaccination decisions by patients or providers; thus,
the association described above cannot prove a causal relationship
between vaccination and GBS.****
[Emphasis added. – ProMED].

Further data collection and analyses of information from EIP and other
surveillance systems are ongoing; a final analysis of the EIP data,
including a self-controlled case series that can control for some of
the confounding that might exist when comparing vaccinated to
unvaccinated persons, is expected to be available in early fall 2010.
Persons with a history of GBS should discuss potential risks and
benefits with their health-care providers before receiving any
influenza vaccine. However, risk assessment should take into account
that influenza and influenza-like illnesses are associated with
significant morbidity and mortality, including a hospitalization rate
of 222 per one million population and a death rate of 9.7 per one
million population for H1N1-associated illness, as well as possible
increased risk for GBS.

****Vaccination remains the most effective method to prevent serious
illness and death from influenza infection.****
[Emphasis added. – ProMED].

– —
Communicated by:
ProMED-mail

[The essential information is that the preliminary analysis comparing
GBS patients hospitalized up to the end of March 2010 indicates that
there were 0.8 excess cases of GBS per one million H1N1 monovalent
vaccinations, a figure similar to that found for seasonal influenza
vaccinations. – Mod.CP]

Michael Wishart | GPH – Infection Control Coordinator

GPH – Quality & Safety Unit (Infection Control) | Greenslopes Private
Hospital
Newdegate Street, Greenslopes QLD 4120
t: 07 3394 7919 | f: 07 3394 7985
e: WishartM@ramsayhealth.com.au | w: http://www.ramsayhealth.com.au

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