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The Vaccine Adverse Event Reporting System:
A Tool for Safety and Surveillance
Jane Woo, MD, MPH
Vaccine Safety Branch
Division of Epidemiology
Office of Biostatistics and Epidemiology
Center for Biologics Evaluation and Research
September 16, 2005
Vaccines
• Highly effective and extremely safe
• A foundation of public health disease
prevention programs
• Different from other pharmaceuticals in
ways that influence safety considerations
• With diseases now controlled by
vaccination and thus rarely observed,
there is a greater focus on safety
Vaccines
• Administered to millions of children
and adults every year
• Mandated for school entry
• Known to cause or contribute to a very
small number of severe injuries
• Suspected by some to be responsible
for a variety of health problems
Temporal Associations Between Vaccinations
and Serious Illnesses Cause Public Concern
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Autism
Attention Deficit Disorder
Brain Damage
Sudden Infant Death
Syndrome (SIDS)
• Cancer
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Asthma
Diabetes
Arthritis
Multiple Sclerosis
Inflammatory Bowel
Disease
Problem: Coincidence or Cause?
• For products with widespread use, some
serious medical events will occur
coincidentally after administration
• Often impossible to ascertain likelihood of
causal connection with vaccine
Example
• 4 million children born in US each year
• Infants receive 15+ immunizations on 4-5
occasions in the first 12 months of life
• About 1/1500 babies dies of SIDS in US each year
• By chance alone, 50-100 babies each year can be
expected to die of SIDS within 2 days of
vaccination
Vaccine Adverse Event Reporting System
(VAERS)
• National system for passive surveillance
• Reports received from health professionals,
vaccine manufacturers, and the public
• > 15,000 reports per year submitted
• Plausible connection of vaccine with serious
events is rare
How can VAERS be used to monitor
vaccine safety?
• Many clinical trials are not large enough to
reveal rare adverse events
• Reports of serious events reviewed
individually; reviewers look for patterns
that could suggest plausible link of an event
to a vaccine
• VAERS data may help generate hypotheses
Data Mining Methods
• Automated techniques that identify events reported
more commonly for one product than others
• Proportional reporting ratios
• Empirical Bayesian methods
• An elevated numerical score may constitute a
“signal” that should be further investigated
• FDA Guidance for Industry on Pharmacovigilance
Planning provides guidelines on signal detection
Data Mining and VAERS
• To study adverse events after a particular vaccine,
we can use recipients of other vaccines as quasi
control group
• Intussusception after rotavirus vaccine
Vaccine 19:4627-34, 2001
• Adverse events after typhoid vaccines
Clin Infect Dis 38:771-779, 2004
• Photophobia after smallpox vaccine
Vaccine 23:1097-1098, 2005
What are the limitations of VAERS?
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Uncertain denominator
Underreporting and incomplete information
Coincidental events inevitable
Reporting rates influenced by media and
other factors
Can almost never disprove causal link
between a vaccine and an adverse event
VAERS Surveillance: Accomplishments
• Overviews of VAERS reports for new vaccines
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Hepatitis A
Varicella
Acellular Pertussis
Pneumococcal conjugate
• Evaluation of data mining techniques
• Identification of safety concerns
– Serious thrombocytopenia
– Alopecia
– Administration of varicella vaccine instead of varicella
immunoglobulin
Contributions to Public Health
• Reassure public that vaccines are safe; if we
find nothing new or unexpected, we want the
public to know
• Highlight any potential concerns and
encourage further study
• Public awareness of continuous surveillance
may enhance confidence in vaccine safety