Autoimmune Thyroid Disease Following Adult Vaccination--a Hypothesis Generating Study Using the Vaccine Adverse Event Reporting System (VAERS)

Background:
It has been postulated that vaccines may play a role in the induction of autoimmune disorders, including autoimmune thyroid disease. However, to date few epidemiologic studies have addressed this topic and results have been varied.

Objectives:
To identify vaccines that might be associated with autoimmune thyroid disease following vaccination.

Methods:
We searched VAERS for primary, U.S. reports received from January 1, 1998 through July 31, 2008 for individuals age 17-65 years containing the following Medical Dictionary for Regulatory Activities (MedDRAź) preferred terms: HYPERTHYROIDISM, HYPOTHYROIDISM, THYROID DISORDER, THYROIDITIS and THYROTOXIC CRISIS. Reports were reviewed and individuals with documented pre-existing thyroid disease were excluded. The published criteria of number of cases (n) ≥3, proportional reporting rate ratio (PRR) ≥2, and chi-square ≥4 were used to detect disproportionate reporting (i.e. elevated proportional reporting compared to rates for other vaccines) for selected vaccines.

Results:
We identified 78 reports of apparent new-onset thyroid disease. The vaccines most commonly reported with thyroid disease included anthrax vaccine adsorbed (AVA) (n=37, 47.4%), hepatitis B vaccine (n=14, 17.9%), and smallpox vaccine (n=8, 10.3%). Disproportionate reporting for any thyroid disease was observed for AVA (n=37, PRR=8.52), typhoid vaccine (n=6, PRR=2.21), and Lyme vaccine (n=6, PRR=2.76). Disproportionate reporting for individual preferred terms included AVA (n=6, PRR=7.21) for hyperthyroidism; AVA (n=21, PRR=12.28), hepatitis B (n=8, PRR=2.13) and typhoid (n=4, PRR=3.21) for hypothyroidism; AVA (n=9, PRR=10.58) and smallpox vaccine (n=4, PRR=5.08) for thyroid disorder; and AVA (n=3, PRR=3.51) and yellow fever vaccine (n=3, PRR=18.79) for thyroiditis.

Conclusions:
VAERS data cannot be used to assess the causality of adverse events. In this review, we found disproportionate reporting for thyroid disease following AVA, hepatitis B, typhoid, yellow fever and Lyme vaccines. A follow up epidemiologic study to evaluate the potential association of thyroid disease with these vaccines is recommended.