The Evidence for Influenza Vaccine
Correct answer? Give all of them.
Let's begin with some history. The etiology of GBS is still unclear, though an antecedent respiratory tract or intestinal infection is reported in about two thirds of cases. The most common inciting organism is Campylobacter jejuni but herpes simplex virus, cytomegalovirus, Epstein-Barr virus, influenza, and others have all been found to be associated with the syndrome. Recently, Zika virus infection was linked to an increase in cases.
Vaccines have also received scrutiny as a potential trigger for GBS. The 1976 vaccination campaign against swine influenza, a product now recognized to have been rushed to market, was followed by increased reports of GBS, raising doubts about safety. This led to the recommendation that influenza vaccine, and possibly others, be avoided because of this increased risk. And that morphed into avoidance of the vaccine in patients with GBS.
Subsequently, a number of studies were conducted to evaluate the association of infections (particularly influenza) and influenza vaccination with the incidence of GBS. Let's look at a couple of them more closely.
A retrospective database review identified persons aged 5 years and older who had been discharged from the hospital with GBS over a 10-year period and then looked at immunizations given to that group. The investigators identified 989 vaccines given to 279 individuals. A wide range of vaccines were administered, with the most common being trivalent inactivated influenza vaccine (405 doses were given to 107 individuals), PPSV23 (151 doses), and tetanus-diphtheria vaccines (143 doses). In almost 4000 person-years of follow-up in the 550 patients with a confirmed diagnosis of GBS, only six patients had a recurrence of GBS. Only one patient had had a vaccine exposure (measles-mumps-rubella, administered 4 months prior to the onset of symptoms) within the year before the recurrence.
A Dutch study asked 245 patients with a previous diagnosis of GBS to respond to a questionnaire inquiring about immunization history and a range of symptoms. Over 100 GBS patients reported having received influenza vaccine following their GBS diagnosis (a total of 775 doses). None of these patients had a recurrence of their GBS.
So it seems that the answer to the question of safety of influenza vaccine in patients with a history of GBS can be definitively answered. The vaccine is safe. The GBS/CIDP Foundation International recommends that the rare person who developed GBS within 4-6 weeks of receipt of a vaccine should avoid that vaccine in the future.
We should also recognize the very small but real potential for new-onset GBS following receipt of influenza vaccine. Several studies have identified a risk for development of GBS following influenza vaccination, estimated at one to two cases per 1 million vaccinations. Almost all cases occurred within 3 weeks post-vaccination, with about half identified in 2 days.
But put that in the context of risk for GBS following an acute influenza infection. A Canadian study using universal healthcare system databases found a lower risk for admission for GBS among vaccinated compared with unvaccinated individuals (1.03 vs 17.2 per million healthcare encounters for influenza). The relative incidence of GBS after influenza was highest in the first week after infection and decreased during the next 6 weeks. So while GBS has been associated with both infection and vaccination, it seems likely that the vaccination option is the more protective route.
GBS in the Time of COVID
While influenza vaccine is always important, it is probably more necessary than ever this year. The potential for a collision of influenza with a second wave of SARS-CoV-2 is very real. The CDC is already urging everyone without contraindications to be vaccinated this season, saying it is even more important during the COVID-19 pandemic than in normal years.
And likely adding to fear of a GBS recurrence is the growing recognition that GBS must be included on the numbingly long list of complications associated with COVID-19.
Will a COVID vaccine also trigger GBS? We'll have to wait and see. But our patients with a history of GBS may be wary of this new vaccine, particularly if the approval process is rushed and adverse effects are not well defined.
Douglas S. Paauw, MD, is the Rathmann Family Foundation Endowed Chair in Patient-Centered Clinical Education and a professor of general internal medicine at the University of Washington. He was elected to Mastership in the American College of Physicians (ACP) in 2009. He is a frequent lecturer at the ACP annual meeting, presenting yearly standing-room-only lectures on drug interactions and medical myths.
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Cite this: Flu Vaccine More Important Than Ever, but Will GBS Patients Believe You? - Medscape - Sep 28, 2020.