Flagged VAERS Signal Pairs: Causality Assessment of the Clearest Signals

Rotavirus vaccine (RotaShield) ↔ Intestinal intussusception / GI haemorrhage

This is the textbook case of a VAERS disproportionality signal that was real and actionable. RotaShield, the first licensed rotavirus vaccine, was withdrawn from the U.S. market in 1999 within a year of launch after passive-surveillance reports of intussusception (a bowel obstruction) triggered a CDC/FDA investigation; subsequent case-control studies confirmed a clear excess risk, concentrated in the days immediately after the first dose. The vaccine was redesigned (RotaTeq, Rotarix), and both current products still carry a small, labeled, and actively monitored excess intussusception risk — smaller than RotaShield's, real, and disclosed on the package insert rather than merely a VAERS artifact. This is the rare case where a top-ranked VAERS signal was independently confirmed by controlled epidemiological study, not just a flagged association.

Not a current dossier topic on this site under the C1–C6 framework; see the Rotavirus vaccine page, Section 4 for this site's own adverse-event summary.

Smallpox vaccine (ACAM2000) ↔ Myocarditis / Pericarditis

Myo/pericarditis after live vaccinia (smallpox) vaccination is one of the best-documented vaccine-cardiac signals in the literature, predating COVID-19 mRNA vaccine myocarditis by two decades. It was identified clearly during the U.S. military's 2002–2003 smallpox vaccination program, when systematic cardiac monitoring (the same monitoring protocol that also generates the many “normal troponin/ECG” entries elsewhere in this dataset) caught a signal CDC and ACIP subsequently acknowledged as a genuine, mechanistically plausible adverse effect of live vaccinia replication. ACIP guidance has since carried cardiac-risk-factor screening and contraindication language for ACAM2000 specifically because of this signal, which is a much stronger form of evidence than a VAERS rank alone — official recommendation language changed because of it.

HPV vaccine (Gardasil) ↔ Abnormal Pap smear / HPV test positive / Cervical dysplasia

These are among the highest PRR values on this entire page — and almost certainly a confounding-by-indication / surveillance-bias artifact, not an injury signal. HPV vaccination and cervical cancer screening (Pap smears, HPV DNA testing) happen in the same population, often at the same clinical visit, and HPV vaccination does not prevent infection with strains a person was already carrying before the shot. A positive HPV test or abnormal smear reported in temporal proximity to vaccination mostly reflects pre-existing infection being detected by routine screening that coincides with the vaccination visit, not a new condition the vaccine caused. This is a deliberately included counter-example: a very high disproportionality score that illustrates why rank alone is not evidence of harm.

Lyme disease vaccine (LYMErix, discontinued) ↔ Arthritis / Polyarthritis

LYMErix (GSK/SmithKline Beecham) was a first-generation Lyme disease vaccine withdrawn from the U.S. market in 2002, three years after approval. Its withdrawal followed a reported signal of autoimmune arthritis, supported at the time by a published molecular-mimicry hypothesis (structural similarity between the vaccine's OspA antigen and human LFA-1, proposed as a trigger in genetically susceptible, HLA-DR4-positive individuals). The manufacturer faced litigation and discontinued the product amid falling sales and the controversy. However, the FDA's and independent epidemiological follow-up studies conducted after withdrawal did not find a confirmed population-level excess of autoimmune arthritis in vaccinated people. LYMErix is a genuinely contested historical case: a real regulatory and commercial withdrawal driven by a safety signal and a biologically plausible mechanism, where the best subsequent epidemiological evidence did not confirm the causal claim. It belongs on this page as an example of a signal that was taken seriously and specifically investigated, with an outcome more ambiguous than either the rotavirus or smallpox examples above.

Rubella-containing vaccine (Meruvax II) ↔ Osteoarthritis / arthropathy

Transient post-vaccination arthralgia and arthritis after rubella-containing vaccines (rubella component of MMR, or monovalent rubella vaccine) is a long-recognized reactogenicity pattern, described in the literature since the 1970s–80s, more common in post-pubertal women than in children. The acute, self-limited form has reasonably strong supporting evidence; chronic or recurrent joint symptoms are less consistently demonstrated across studies, and most reviews describe the association as biologically plausible (immune-mediated, similar to natural rubella infection's own joint-symptom pattern) but not as strongly or independently confirmed outside spontaneous-report data as the rotavirus or smallpox examples above.

See also the MMR vaccine page for VAERS category breakdowns that include arthralgia.

DTaP+IPV+Hib (Pentacel) ↔ Post-tussive vomiting

Included as a contrast case: a very high disproportionality score attached to a mild, well-characterized, and expected reactogenicity event (vomiting following a coughing fit, a known feature of pertussis-containing vaccine reactogenicity profiles) rather than a serious or contested adverse event. High rank does not imply high severity.