Surveillance for Guillain-Barré syndrome after 2015-2016 and 2016-2017 influenza vaccination of Medicare beneficiaries

Vaccine patterns among older adults with Guillain-Barré syndrome and matched comparators, 2006-2019

BACKGROUND

Some vaccines have a small risk of triggering Guillain-Barré syndrome (GBS), an autoimmune disorder where nerve damage leads to paralysis. There is a CDC precaution for patients whose GBS was associated with an influenza or tetanus toxoid-containing vaccine (GBS occurring within 42 days following vaccination).

METHODS

We described vaccine patterns before and after a GBS diagnosis with a matched cohort design in a 20% random sample of fee-for-service Medicare enrollees. We defined the index date as an ICD-9-CM or ICD-10-CM GBS diagnosis code in the primary position of an inpatient claim. We matched each GBS patient to five non-GBS comparators on sex, exact age, racial and ethnic category, state of residence and the month of preventive health visits during baseline; used weighting to balance covariates; and measured frequency of vaccines received per 100 people during year before and after the index date using the weighted mean cumulative count (wMCC).

RESULTS

We identified 1567 patients with a GBS diagnosis with at least 1 year of prior continuous enrollment in Medicare A and B that matched to five comparators each. The wMCCs in the 1 year before the index date were similar for both groups, with a wMCC of 74 vaccines/100 people in the GBS group (95% CI 71, 77). Within 1 year after the index date, patients with GBS had received 26 vaccines/100 people (95% CI 23, 28), which was 41 fewer vaccines than matched non-GBS comparators (95% CI -44, -38). Among GBS patients, 11% were diagnosed with GBS within 42 days after a vaccine.

CONCLUSIONS

GBS diagnosis has a strong impact on reducing subsequent vaccination even though there is no warning or precaution about future vaccines for most patients diagnosed with GBS. These data suggest discordance between clinical practice and current vaccine recommendations.

Assessment of potential adverse events following the 2022-2023 seasonal influenza vaccines among U.S. adults aged 65 years and older

BACKGROUND

While safety of influenza vaccines is well-established, some studies have suggested potential associations between influenza vaccines and certain adverse events (AEs). This study examined the safety of the 2022-2023 influenza vaccines among U.S. adults ≥ 65 years.

METHODS

A self-controlled case series compared incidence rates of anaphylaxis, encephalitis/encephalomyelitis, Guillain-Barré Syndrome (GBS), and transverse myelitis following 2022-2023 seasonal influenza vaccinations (i.e., any, high-dose or adjuvanted) in risk and control intervals among Medicare beneficiaries ≥ 65 years. We used conditional Poisson regression to estimate incidence rate ratios (IRRs) and 95 % confidence intervals (CIs) adjusted for event-dependent observation time and seasonality. Analyses also accounted for uncertainty from outcome misclassification where feasible. For AEs with any statistically significant associations, we stratified results by concomitant vaccination status.

RESULTS

Among 12.7 million vaccine recipients, we observed 76 anaphylaxis, 276 encephalitis/encephalomyelitis, 134 GBS and 75 transverse myelitis cases. Only rates of anaphylaxis were elevated in risk compared to control intervals. With all adjustments, an elevated, but non-statistically significant, anaphylaxis rate was observed following any (IRR: 2.40, 95% CI: 0.96-6.03), high-dose (IRR: 2.31, 95% CI: 0.67-7.91), and adjuvanted (IRR: 3.28, 95% CI: 0.71-15.08) influenza vaccination; anaphylaxis IRRs were 2.54 (95% CI: 0.49-13.05) and 1.64 (95% CI: 0.38-7.05) for persons with and without concomitant vaccination, respectively.

CONCLUSIONS

Rates of encephalitis/encephalomyelitis, GBS, or transverse myelitis were not elevated following 2022-2023 seasonal influenza vaccinations among U.S. adults ≥ 65 years. There was an increased rate of anaphylaxis following influenza vaccination that may have been influenced by concomitant vaccination.

Vaccine patterns among patients diagnosed with Guillain-Barré Syndrome and matched counterparts in a Medicare supplemental population, 2000-2020

Some vaccines have a small risk of Guillain-Barré Syndrome (GBS), a rare autoimmune disorder characterized by paralysis if untreated. The CDC's Advisory Committee on Immunization Practices (ACIP) guidelines do not consider GBS a precaution for future vaccines unless GBS developed within six weeks after a tetanus-toxoid-containing vaccine or influenza vaccine. Our goal was to describe vaccine patterns before and after GBS diagnosis. We matched each of 709 patients diagnosed with GBS from 2002 to 2020 with Medicare supplemental insurance to 10 counterparts without GBS (1:10) on age and sex. Propensity score-based weighting balanced covariates between groups, and we estimated weighted mean cumulative counts (wMCC) of vaccines/person before and after GBS diagnosis. Among patients with GBS, 7% were diagnosed within 42 days after a vaccine. Prior to GBS diagnosis, the wMCC of vaccines per person was similar between GBS cases and matched counterparts, but after two years of follow-up, GBS patients received 21 fewer vaccines/100 people than counterparts (wMCC difference -0.21 vaccines/person, 95% CI -0.24 to -0.18); GBS patients received 16 vaccines/100 people while matched counterparts received 36/100. Vaccine use was reduced following GBS diagnosis despite no ACIP precaution for most (93%) patients in this study. The observed drop in vaccines after GBS diagnosis indicates a disconnect between clinical practice and current recommendations.

Surveillance of COVID-19 vaccine safety among elderly persons aged 65 years and older

BACKGROUND

Monitoring safety outcomes following COVID-19 vaccination is critical for understanding vaccine safety especially when used in key populations such as elderly persons age 65 years and older who can benefit greatly from vaccination. We present new findings from a nationally representative early warning system that may expand the safety knowledge base to further public trust and inform decision making on vaccine safety by government agencies, healthcare providers, interested stakeholders, and the public.

METHODS

We evaluated 14 outcomes of interest following COVID-19 vaccination using the US Centers for Medicare & Medicaid Services (CMS) data covering 30,712,101 elderly persons. The CMS data from December 11, 2020 through Jan 15, 2022 included 17,411,342 COVID-19 vaccinees who received a total of 34,639,937 doses. We conducted weekly sequential testing and generated rate ratios (RR) of observed outcome rates compared to historical (or expected) rates prior to COVID-19 vaccination.

FINDINGS

Four outcomes met the threshold for a statistical signal following BNT162b2 vaccination including pulmonary embolism (PE; RR = 1.54), acute myocardial infarction (AMI; RR = 1.42), disseminated intravascular coagulation (DIC; RR = 1.91), and immune thrombocytopenia (ITP; RR = 1.44). After further evaluation, only the RR for PE still met the statistical threshold for a signal; however, the RRs for AMI, DIC, and ITP no longer did. No statistical signals were identified following vaccination with either the mRNA-1273 or Ad26 COV2.S vaccines.

INTERPRETATION

This early warning system is the first to identify temporal associations for PE, AMI, DIC, and ITP following BNT162b2 vaccination in the elderly. Because an early warning system does not prove that the vaccines cause these outcomes, more robust epidemiologic studies with adjustment for confounding, including age and nursing home residency, are underway to further evaluate these signals. FDA strongly believes the potential benefits of COVID-19 vaccination outweigh the potential risks of COVID-19 infection.

Population-Based Incidence of Guillain-Barré Syndrome During Mass Immunization With Viral Vaccines: A Pooled Analysis

Misunderstanding temporal coincidence of adverse events during mass vaccination and invalid assessment of possible safety concerns have negative effects on immunization programs, leading to low immunization coverage. We conducted this systematic review and meta-analysis to identify the incidence rates of GBS that are temporally associated with viral vaccine administration but might not be attributable to the vaccines. By literature search in Embase and PubMed, we included 48 publications and 2,110,441,600 participants. The pooled incidence rate of GBS was 3.09 per million persons (95% confidence interval [CI]: 2.67 to 3.51) within six weeks of vaccination, equally 2.47 per 100,000 person-year (95%CI: 2.14 to 2.81). Subgroup analyses illustrated that the pooled rates were 2.77 per million persons (95%CI: 2.47 to 3.07) for individuals who received the influenza vaccine and 2.44 per million persons (95%CI: 0.97 to 3.91) for human papillomavirus (HPV) vaccines, respectively. Our findings evidence the GBS-associated safety of virus vaccines. We present a reference for the evaluation of post-vaccination GBS rates in mass immunization campaigns, including the SARS-CoV-2 vaccine.

COVID-19 vaccination and Guillain-Barré syndrome: analyses using the National Immunoglobulin Database

Vaccination against viruses has rarely been associated with Guillain-Barré syndrome (GBS), and an association with the COVID-19 vaccine is unknown. We performed a population-based study of National Health Service data in England and a multicentre surveillance study from UK hospitals to investigate the relationship between COVID-19 vaccination and GBS. Firstly, case dates of GBS identified retrospectively in the National Immunoglobulin Database from 8 December 2021 to 8 July 2021 were linked to receipt dates of COVID-19 vaccines using data from the National Immunisation Management System in England. For the linked dataset, GBS cases temporally associated with vaccination within a 6-week risk window of any COVID-19 vaccine were identified. Secondly, we prospectively collected incident UK-wide (four nations) GBS cases from 1 January 2021 to 7 November 2021 in a separate UK multicentre surveillance database. For this multicentre UK-wide surveillance dataset, we explored phenotypes of reported GBS cases to identify features of COVID-19 vaccine-associated GBS. Nine hundred and ninety-six GBS cases were recorded in the National Immunoglobulin Database from January to October 2021. A spike of GBS cases above the 2016-2020 average occurred in March-April 2021. One hundred and ninety-eight GBS cases occurred within 6 weeks of the first-dose COVID-19 vaccination in England [0.618 cases per 100,000 vaccinations; 176 ChAdOx1 nCoV-19 (AstraZeneca), 21 tozinameran (Pfizer) and one mRNA-1273 (Moderna)]. The 6-week excess of GBS (compared to the baseline rate of GBS cases 6-12 weeks after vaccination) occurred with a peak at 24 days post-vaccination; first-doses of ChAdOx1 nCoV-19 accounted for the excess. No excess was seen for second-dose vaccination. The absolute number of excess GBS cases from January-July 2021 was between 98-140 cases for first-dose ChAdOx1 nCoV-19 vaccination. First-dose tozinameran and second-dose of any vaccination showed no excess GBS risk. Detailed clinical data from 121 GBS patients were reported in the separate multicentre surveillance dataset during this timeframe. No phenotypic or demographic differences identified between vaccine-associated and non-vaccinated GBS cases occurring in the same timeframe. Analysis of the linked NID/NIMS dataset suggested that first-dose ChAdOx1 nCoV-19 vaccination is associated with an excess GBS risk of 0.576 (95% confidence interval 0.481-0.691) cases per 100 000 doses. However, examination of a multicentre surveillance dataset suggested that no specific clinical features, including facial weakness, are associated with vaccination-related GBS compared to non-vaccinated cases. The pathogenic cause of the ChAdOx1 nCoV-19 specific first dose link warrants further study.

New relapse of multiple sclerosis and neuromyelitis optica as a potential adverse event of AstraZeneca AZD1222 vaccination for COVID-19

We report on nine patients (eight cases of MS and one case of NMOSD) who presented a disease relapse in close temporal association with their first AZD1222 vaccination dose against COVID-19. These patients had been stable for a median period of six years, with no evidence of disease activity and no change in their medication. After a median of 13 days (7 to 25 days) from vaccination, they developed a new relapse with increased disability and new lesions on magnetic resonance imaging. Although this association may be rare, it might be an adverse event of AZD1222.

Systematic review of the efficacy, effectiveness and safety of high-dose seasonal influenza vaccines for the prevention of laboratory-confirmed influenza in individuals ≥18 years of age

This review sought to assess the efficacy, effectiveness and safety of high-dose inactivated influenza vaccines (HD-IIV) for the prevention of laboratory-confirmed influenza in individuals aged 18 years or older. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials (RCTs) and non-randomised studies of interventions (NRSIs) were included. The search returned 28,846 records, of which 36 studies were included. HD-IIV was shown to have higher relative vaccine efficacy in preventing influenza compared with standard-dose influenza vaccines (SD-IIV3) in older adults (Vaccine effectiveness (VE) = 24%, 95% CI 10-37, one RCT). One NRSI demonstrated significant effect for HD-IIV3 against influenza B (VE = 89%, 95% CI 47-100), but not for influenza A(H3N2) (VE = 22%, 95% CI -82 to 66) when compared with no vaccination in older adults. HD-IIV3 showed significant relative effect compared with SD-IIV3 for influenza-related hospitalisation (VE = 11.8%, 95% CI 6.4-17.0, two NRSIs), influenza- or pneumonia-related hospitalisation (VE = 13.7%, 95% CI 9.5-17.7, three NRSIs), influenza-related hospital encounters (VE = 13.1%, 95% CI 8.4-17.7, five NRSIs), and influenza-related office visits (VE = 3.5%, 95% CI 1.5-5.5, two NRSIs). For safety, HD-IIV were associated with significantly higher rates of local and systemic adverse events compared with SD-IIV (combined local reactions, pain at injection site, swelling, induration, headache, chills and malaise). From limited data, compared with SD-IIV, HD-IIV were found to be more effective in the prevention of laboratory-confirmed influenza, for a range of proxy outcome measures, and associated with more adverse events.

Postmarketing safety surveillance of high-dose quadrivalent influenza vaccine: Reports to the Vaccine Adverse Event Reporting System

On November 4, 2019, the Food and Drug Administration approved high-dose quadrivalent influenza vaccine (Fluzone High-Dose Quadrivalent; QIV-HD) for active immunization for the prevention of influenza disease in individuals 65 years of age and older. A prelicensure randomized, active-controlled, modified double-blind trial did not reveal any major differences in adverse events following QIV-HD versus Fluzone High-Dose (trivalent). To improve our understanding of the safety profile of QIV-HD, we reviewed and summarized reports of adverse events after QIV-HD to the Vaccine Adverse Event Reporting System (VAERS). From July 30, 2020 through June 30, 2021, VAERS received 2,122 reports after QIV-HD. The vast majority (2,018; 95.1%) were non-serious and included events that had been observed in the prelicensure clinical trial, such as injection site reactions, fever, headache, and nausea. The most common serious events included Guillain-Barré syndrome, cellulitis or other local reactions, constitutional signs/symptoms (e.g., fever), and cardiovascular events. Our review did not reveal any new safety concerns. This information may enable policy makers, health officials, clinicians, and patients to make a more informed decision regarding vaccination strategies.

Acute Bulbar Palsy-Plus Variant of Guillain-Barré Syndrome in a 3-Year-Old Girl

We present a case of a 3-year-old girl who rapidly developed bilateral facial palsy, dysphagia, dysphonia, areflexia, and ataxia soon after receiving an influenza vaccine. Brain and spine Magnetic resonance imaging (MRI) scans with and without contrast showed enhancement of cranial nerves III, V, VII, and X, as well as the anterior and posterior cervical spinal and cauda equina roots. cerebrospinal fluid (CSF) studies showed white blood cell count of 19 cells/cm², glucose 81 mg/dL, and protein 116 mg/dL, with negative infectious and autoimmune labs. Serum IgM and IgG antibodies against GM1, GD1a, GD1b, GM2, GT1A, GQ1b were negative. The patient was treated with intravenous immunoglobulin, which led to a full recovery. Upon three-month follow-up, her neurologic examination demonstrated normal cranial nerves, reflexes, and gait. Her presentation was most consistent with the acute bulbar palsy plus (ABPp) variant of Guillain-Barré syndrome (GBS), a rare and challenging diagnosis especially in her age group.

Natural History of Coronavirus Disease 2019: Risk Factors for Hospitalizations and Deaths Among >26 Million US Medicare Beneficiaries

BACKGROUND

The current study was performed to evaluate risk factors for severe coronavirus disease 2019 (COVID-19) outcomes among Medicare beneficiaries during the pandemic's early phase.

METHODS

In a retrospective cohort study covering Medicare fee-for-service beneficiaries, we separated out elderly residents in nursing homes (NHs) and those with end-stage renal disease (ESRD) from the primary study population of individuals age ≥65 years. Outcomes included COVID-19 hospital encounters and COVID-19-associated deaths. We estimated adjusted odds ratios (ORs) using logistic regression.

RESULTS

We analyzed 25 333 329 elderly non-NH beneficiaries without ESRD, 653 966 elderly NH residents, and 292 302 patients with ESRD. COVID-related death rates (per 10 000) were much higher among elderly NH residents (275.7) and patients with ESRD (60.8) than in the primary study population (5.0). Regression-adjusted clinical predictors of death among the primary population included immunocompromised status (OR, 1.43), frailty index conditions such as cognitive impairment (3.16), and other comorbid conditions, including congestive heart failure (1.30). Demographic-related risk factors included male sex (OR, 1.77), older age (3.09 for 80- vs 65-year-olds), Medicaid dual-eligibility status (2.17), and racial/ethnic minority. Compared with whites, ORs were higher for blacks (2.47), Hispanics (3.11), and Native Americans (5.82). Results for COVID-19 hospital encounters were consistent.

CONCLUSIONS

Frailty, comorbid conditions, and race/ethnicity were strong risk factors for COVID-19 hospitalization and death among the US elderly.

Postmarketing safety surveillance of quadrivalent recombinant influenza vaccine: Reports to the vaccine adverse event reporting system

On October 7, 2016, the Food and Drug Administration approved recombinant hemagglutinin quadrivalent influenza vaccine (RIV4) (Spodoptera frugiperda cell line; Flublok Quadrivalent) for active immunization for the prevention of influenza disease in individuals 18 years of age and older. Clinical trials did not reveal any major differences in adverse events or serious adverse events following Flublok Quadrivalent versus standard-dose quadrivalent inactivated influenza vaccine. To improve our understanding of the safety profile of this vaccine, we reviewed and summarized adverse event reports after Flublok Quadrivalent administration to the Vaccine Adverse Event Reporting System (VAERS). Through June 30, 2020, VAERS received 849 reports after RIV4 vaccination. The vast majority (810; 95%) were non-serious. Among serious events, there were 10 cases of Guillain-Barré syndrome, including 5 people who required mechanical ventilation and 2 people who died. Many allergic reactions were reported as non-serious, but required interventions to treat a life-threatening event, e.g., epinephrine, nebulizers, albuterol, glucocorticoids, and supplemental oxygen. Two people experienced a positive rechallenge (i.e., allergic reactions after repeated vaccination with RIV4), including a person who-despite premedication with antihistamines-developed respiratory difficulties, required epinephrine, and was transported to the emergency department. The occurrence of anaphylaxis and other allergic reactions in some individuals may reflect an underlying predisposition to atopy that may manifest itself after an exposure to any drug or vaccine, and does not necessarily suggest that Flublok Quadrivalent is particularly allergenic. Postmarketing safety surveillance will continue to be vital for understanding the benefits and risks of quadrivalent recombinant influenza vaccine.

Prediction of post-vaccination Guillain-Barré syndrome using data from a passive surveillance system

Purpose

Severe adverse events (AEs), such as Guillain‐Barré syndrome (GBS) occur rarely after influenza vaccination. We identify highly associated AEs with GBS and develop prediction models for GBS using the US Vaccine Adverse Event Reporting System (VAERS) reports following trivalent influenza vaccination (FLU3).

Methods

This study analyzed 80 059 reports from the US VAERS between 1990 and 2017. Several AEs were identified as highly associated with GBS and were used to develop the prediction model. Some common and mild AEs that were suspected to be underreported when GBS occurred simultaneously were removed from the final model. The analyses were validated using European influenza vaccine AEs data from EudraVigilance.

Results

Of the 80 059 reports, 1185 (1.5%) were annotated as GBS related. Twenty‐four AEs were identified as having strong association with GBS. The full prediction model, using age, sex, and all 24 AEs achieved an area under the receiver operating characteristic (ROC) curve (AUC) of 85.4% (90% CI: [83.8%, 86.9%]). After excluding the nine (e.g., pruritus, rash, injection site pain) likely underreported AEs, the final AUC became 77.5% (90% CI: [75.5%, 79.6%]). Two hundred and one (0.25%) reports were predicted as of high risk of GBS (predicted probability >25%) and 84 actually developed GBS.

Conclusion

The prediction performance demonstrated the potential of developing risk‐prediction models utilizing the VAERS cohort. Excluding the likely underreported AEs sacrificed some prediction power but made the model more interpretable and feasible. The high absolute risk of even a small number of AE combinations suggests the promise of GBS prediction within the VAERS dataset.

Guillain-Barré Syndrome After High-Dose Influenza Vaccine Administration in the United States, 2018-2019 Season

BACKGROUND

The Vaccine Safety Datalink (VSD) identified a statistical signal for an increased risk of Guillain-Barré syndrome (GBS) in days 1-42 after 2018-2019 high-dose influenza vaccine (IIV3-HD) administration. We evaluated the signal using Medicare.

METHODS

We conducted early- and end-of-season claims-based self-controlled risk interval analyses among Medicare beneficiaries ages ≥65 years, using days 8-21 and 1-42 postvaccination as risk windows and days 43-84 as control window. The VSD conducted chart-confirmed analyses.

RESULTS

Among 7 453 690 IIV3-HD vaccinations, we did not detect a statistically significant increased GBS risk for either the 8- to 21-day (odds ratio [OR], 1.85; 95% confidence interval [CI], 0.99-3.44) or 1- to 42-day (OR, 1.31; 95% CI, 0.78-2.18) risk windows. The findings from the end-of-season analyses were fully consistent with the early-season analyses for both the 8- to 21-day (OR, 1.64; 95% CI, 0.92-2.91) and 1- to 42-day (OR, 1.12; 95% CI, 0.70-1.79) risk windows. The VSD's chart-confirmed analysis, involving 646 996 IIV3-HD vaccinations, with 1 case each in the risk and control windows, yielded a relative risk of 1.00 (95% CI, 0.06-15.99).

CONCLUSIONS

The Medicare analyses did not exclude an association between IIV3-HD and GBS, but it determined that, if such a risk existed, it was similar in magnitude to prior seasons. Chart-confirmed VSD results did not confirm an increased risk of GBS.

Antigenic Variability a Potential Factor in Assessing Relationship Between Guillain Barré Syndrome and Influenza Vaccine - Up to Date Literature Review

Guillain-Barré syndrome (GBS) is a possible serious adverse event of the influenza vaccine but it is yet to be proven. The objective of our traditional literature review is to assess the potential relationship between GBS and influenza vaccine. A traditional literature review has been carried out by selecting 26 articles from PubMed published between 2011 and 2020. Twenty-six articles met the selection criteria (eight observational studies, four systematic literature review, three meta-analyses, two case-control, two retrospective cohort, and seven case series). Selected studies were focused on monitoring the safety of influenza vaccines, the relative safety of pandemic and seasonal influenza vaccines, influenza vaccine a potential etiology of GBS, and pathogenesis of post-vaccination GBS. Few studies have shown a higher incidence of GBS with a pandemic influenza vaccine compared to the seasonal influenza vaccine, while several studies have concluded a small increase in the possibility of GBS following any type of influenza vaccine. There were some studies that estimated no association possibly due to the presence of confounding factors such as influenza-like illness, low power of the study, and reporting bias in post-vaccination surveillance programs. GSB should be taken into consideration as one of the less common but serious side effects of the influenza vaccine but it should not adversely affect the acceptance of the influenza vaccination program. Continuous monitoring of influenza vaccine safety should be performed regularly.

A simulation study of the statistical power and signaling characteristics of an early season sequential test for influenza vaccine safety

PURPOSE

The US Food and Drug Administration monitors the risk of Guillain-Barré syndrome (GBS) following influenza vaccination using several data sources including Medicare. In the 2017 to 2018 season, we transitioned our near real-time surveillance in Medicare to more effectively detect large GBS risk increases early in the season while avoiding false positives.

METHODS

We conducted a simulation study examining the ability of the updating sequential probability ratio test (USPRT) to detect substantially elevated GBS risk in the 8- to 21-day postvaccination versus 5× to 30× the historical rate. We varied the first testing week (weeks 5-8) and the null rate (1×-3×) and evaluated power. We estimated signal probability and the risk ratio (RR) after signaling when high-risk seasons were rare.

RESULTS

Applying fixed alternatives, we found >80% power to detect a risk 30× the historical rate in week 5 for the 1× null and in week 6 for the 1.5× to 3× nulls. Nearly all testing schedules had >80% power for a 5× risk by week 11. To test the robustness of USPRT, we further simulated seasons where 1% were true high-risk seasons. Using a 1× null led to 10% of seasons signaling by week 11 (median RR approximately 1.4), which decreased to approximately 1% with the ≥2.5× null (median RR approximately 16.0).

CONCLUSIONS

On the basis of the results from this simulation and subsequent consultations with experts and stakeholders, we specified USPRT to test continuously from weeks 7 to 11 using the null hypothesis that the observed GBS rate was 2.5× the historical rate. This helped improve the ability of USPRT to provide early detection of GBS risk following influenza vaccination as part of a multilayered system of surveillance.

Surveillance for Guillain-Barré syndrome after influenza vaccination among U.S. Medicare beneficiaries during the 2017-2018 season

BACKGROUND

The U.S. Food and Drug Administration and the Centers for Medicare & Medicaid Services have been actively monitoring the risk of Guillain-Barré syndrome (GBS) following influenza vaccination among Fee-for-Service (FFS) Medicare beneficiaries every season since 2008. We present our evaluation of the GBS risk following influenza vaccinations during the 2017-2018 season.

METHODS

We implemented a multilayered approach to active safety surveillance that included near real-time surveillance early in the season, comparing GBS rates post-vaccination during the 2017-2018 season with rates from five prior seasons using the Updating Sequential Probability Ratio Test (USPRT), and end-of-season self-controlled risk interval (SCRI) analyses.

RESULTS

We identified approximately 16 million influenza vaccinations. The near real-time surveillance did not signal for a potential 2.5-fold increased GBS risk either in days 8-21 or 1-42 post-influenza vaccination. In the SCRI analyses, we did not detect statistically significant increased GBS risks among influenza-vaccinated Medicare beneficiaries ≥65 years for either the 8-21 or 1-42-day risk windows for all seasonal vaccines combined, high-dose vaccine, or standard-dose vaccines; we did detect an increased GBS risk in days 8-21 post-vaccination for individuals vaccinated with the adjuvanted vaccine (OR: 3.75; 95% CI: 1.01, 13.96), although this finding was not statistically significant after multiplicity adjustment (p = 0.146).

CONCLUSIONS

Our multilayered surveillance approach-which allows for early detection of elevated GBS risk and provides reliable end-of-season SCRI estimates of effect size-did not identify an increased GBS risk following 2017-2018 influenza vaccinations. The slightly increased GBS risk with the adjuvanted vaccine, which was not statistically significant following multiplicity adjustment, is consistent with the package inserts of all U.S.-licensed influenza vaccines, which warn of a potential low increased GBS risk. The benefits of influenza vaccines in preventing morbidity and mortality heavily outweigh this potential risk.