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Inadvertent Inoculation: Frequency & Susceptible Populations

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Inadvertent inoculation can be by autoinoculation or contact inoculation.

Inadvertent Inoculation Cases per 1,000,000 Primary Vaccinations(*)

Age (yrs)

1968 National

1968 10-State

1-4 34.4 615.1
5-19 16.7 393.0
>20 13.9 636.4
Totals >1 yr 27.1 532.0

As indicated from these data, inadvertent inoculation is one of the most common adverse events following primary vaccination. It is far less common after revaccination but the threat of transfer to contacts remains. 

Although no age group is spared, infants and children are most susceptible to more extensive inoculations because of their tendency to scratch an itching vaccination site. Older individuals may be able to control such scratching, despite the itching, but younger individuals most often cannot. Older individuals tend to have fewer lesions but they are seen more frequently. Older individuals implant virus frequently on the face as a result of inadvertent contamination of the hands or via fomites. Minute injuries, such as occur in shaving establish the potential for implantation.

* Numbers rounded to the nearest tenth, total number of vaccinations estimated in both studies. Observations missing age were distributed according to the existing age distribution for inadvertent inoculation.
Case sources include: American Red Cross Vaccinia Immune Globulin (VIG) distribution system, Red Cross VIG consultants, State and Territorial Epidemiologists, Burroughs-Wellcome Thiosemicarbazone distribution list, smallpox vaccine manufacturers complication reporting files, state reports to the Encephalitis Surveillance Unit of the National Communicable Disease Center (NCDC), and specimen submissions for vaccinia testing to the Viral Exanthems Unit of NCDC.
Case sources include: Physician reporting via survey in 10 states with active case information follow-up and chart review for post-vaccinial encephalitis and vaccinia necrosum reports.

Susceptible Populations

Individuals who are particularly susceptible to inadvertent inoculation, either by autoinoculation or contact inoculation, include those with: 

  Skin disorders with open lesions
  Inflammatory eye diseases

These individuals are also more susceptible to serious disease as a consequence. 


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