Arm Paralysis After Routine Childhood Vaccinations: Application of Advanced Molecular Methods to the Causality Assessment of an Adverse Event After Immunization

Lessons learned from COVID-19, H1N1, and routine vaccine pharmacovigilance in the United States: a path to a more robust vaccine safety program

INTRODUCTION

Vaccine pharmacovigilance is an essential component of vaccine safety programs. Vaccine pharmacovigilance refers to detecting uncommon adverse events following immunization (AEFI), determining whether they are due to the vaccine or are only a coincidence, and, for those AEFI considered related to vaccination, characterizing them further. When AEFI are due to vaccination, it is important to characterize the attributable risk and ascertain the biological mechanism causing the adverse reaction to inform efforts to prevent or mitigate the risk. A robust post-authorization safety system is necessary for vaccine decision-making, clinical recommendations, vaccine compensation, and vaccine communication and confidence.

AREAS COVERED

This paper describes the key characteristics of vaccine pharmacovigilance programs, reviews US vaccine pharmacovigilance for routine vaccination programs, COVID-19, and H1N1, and makes recommendations for improving future vaccine safety systems.

EXPERT OPINION

The key characteristics of vaccine pharmacovigilance programs include passive surveillance, active surveillance, clinical investigation and special studies, and causality assessment. Recent examples illustrate the strengths of US pharmacovigilance systems, including systems for passive and active surveillance, as well as areas for improvement, including study of pathogenesis, consistent funding, and leadership. We make recommendations that would, if implemented, further strengthen the vaccine safety system for future routine and pandemic immunizations.

Vaccine Strain and Wild-Type Clades of Varicella-Zoster Virus in Central Nervous System and Non-CNS Disease, New York State, 2004-2019

Since the introduction of the varicella-zoster virus (VZV) vaccine in the United States in 1995, there has been a dramatic decrease in both the number and severity of varicella cases. However, VZV surveillance data and information on the VZV clade distribution in central nervous system (CNS) disease and non-CNS disease in New York State is not available. To investigate this, cerebrospinal fluid (CSF) samples from patients with encephalitis or meningitis and non-CSF samples from patients with non-CNS disease manifestations consistent with VZV, collected from 2004 to 2019, were tested with molecular VZV assays. A total of 341 CSF and 1,398 non-CSF samples that tested positive by a VZV-specific real-time PCR assay were further characterized as wild-type or vaccine strain by 3 biallelic real-time PCR assays targeting single nucleotide polymorphism (SNP) markers in open reading frame (ORF) 62. Genotyping was then performed on wild-type strains by conventional PCR and sequencing of 500-bp regions in ORFs 21, 22, and 50. Sequence analysis identified clades 1 to 5 in both sample types with a virtually identical clade distribution between CSF and non-CSF samples. In addition, 19 clade 6 and 13 clade 9 samples were detected in non-CSF samples after implementation of an expanded genotyping scheme, including ORF 29, 38, and 67. These clades were not detected in any CSF samples. Finally, a total of 28 vaccine strains were detected, 25 in the non-CSF samples and 3 in the CSF samples. All three cases of vaccine strain with CNS involvement experienced relatively minor symptoms of aseptic meningitis and fully recovered. These results support the evidence that while the VZV vaccine is capable of causing CNS disease, it is still a rare event and symptoms are typically less severe than those caused by wild-type infection.

Varicella Virus Vaccination in the United States

Varicella zoster virus (VZV) is the cause of chickenpox (varicella) and shingles (zoster), and was once responsible for over 4 million infections in the United States annually. The development of a live attenuated VZV vaccine was initially viewed with extreme skepticism. Nonetheless, a VZV vaccine was developed in the 1970s by Takahashi and his colleagues in Japan and was eventually licensed in the US. It is now known to be one of the safest and most effective vaccines available and is administered worldwide. Here are described important factors that contributed to the successful research and licensure of the highly successful VZV vaccine.