Post-Event Operational Issues

Vaccination Strategies to Contain an Outbreak

Considerations

The number of available doses could make the difference between focusing only on the high-risk ring of direct contacts and their close contacts, or expanding the focus to include and entire community or population.

The extent of the outbreak is also important. Is the outbreak confined to one small area or are there multiple areas in various places around the country? Localized cases may allow vaccination to be focused on a smaller number of people. Multiple initial cases in several areas of a country could indicate that multiple intentional introductions of the virus has occurred and lead to an early decision to immunize the entire population.

During the eradication program conducted in the 1970s, it was determined that vaccination focused primarily on the close contacts to smallpox cases was very effective in halting outbreaks, even in areas where there was a low percentage of previous vaccination. Occasionally, depending on the makeup of the area, number of contacts, or contact tracing resources, broader vaccination was added to help break a chain of transmission. Broader vaccination was possible because vaccine was readily available, giving options to public health planners that they may not have currently.

Defining a vaccination strategy with the smallpox realities today. Current realities being:

  1. No known cases of smallpox at this time.
  2. It is unclear if there are individuals, groups, or governments that have smallpox for use as a weapon.
  3. Since regular vaccination with smallpox was stopped worldwide over 20 years ago, there are entire populations who are vulnerable to infection with smallpox virus.
  4. There are many more people at risk from adverse events from vaccination than there were 20 years ago (e.g. more people with immune system disorders, transplants, and cancer treatment).
  5. There are limited vaccine supplies worldwide. Even if we wanted to immunize everyone in the world today, we couldn’t do it with the supplies of vaccine we have.

Ring Vaccination Strategy

The “Ring Vaccination” strategy has been used successfully in the past to stop smallpox outbreaks. It was the only strategy used for control of smallpox in Australia. This strategy involves vaccinating the contacts of the case, and their own close contacts in order to interrupt the chain of transmission. Vaccinating the close contacts of the contact (e.g. household members of contact) provides protection to individuals who are likely to be exposed if the contact develops the disease while under surveillance at home. The strategy provides a “ring” of vaccinated/protected individuals around the case their contacts to prevent further transmission. After a case and their contacts are identified, anyone coming into contact with them while they are potentially infectious would be vaccinated and protected. This has been so useful because we know that most transmission of smallpox occurs from close contact.

While the ring vaccination strategy is our primary means of stopping the immediate chain of transmission, we know that it depends on the prompt identification of contacts, which means having trained personnel who can do this. This strategy allows us to maximize the effectiveness of a limited vaccine supply by targeting vaccination to those at highest risk while minimizing the risks of adverse events by vaccinating only those who really must be vaccinated because of their high risk of infection.

Contact Definition

Primary Contact - A primary contact is a person in contact to a confirmed, probable or suspected case of smallpox during the infectious period. Primary contacts include both household and non-household contacts.

Secondary Contact (contacts of contact) - A secondary contact (or contact of contact) is a household contact of a primary contact or a person who works in the household of a primary contact.

Contact Vaccination

High-risk contacts are defined as people having close, face-to-face contact with a smallpox case, usually within 2 meters or 6.5 feet, and/or household members of a smallpox case. If we can immunize these contacts within 3 days of exposure, we might be able to prevent a case completely, or at least lessen the severity of the disease if they do develop the disease. These close contacts should be monitored for fever, the first indication of possible smallpox infection, for at least 18 days from their last exposure to the smallpox case.

Contraindications for Vaccination of Contacts

For the close contacts of a smallpox case, there are NO contraindications for the use of vaccine because they are at high risk for developing the disease. Development of smallpox would present a greater risk to the contact than adverse events. Adverse events may be treatable with vaccinia immune globulin (VIG) or newer antiviral medications (Cidofovir), while there is no known treatment for smallpox. In general, the risk of developing smallpox for face-to-face contacts outweighs the risk of developing vaccine complications for those contacts with contraindications to vaccination.

Contacts of contacts who do not have contraindications should be vaccinated.

Contacts of contacts who have vaccine contraindications (e.g. immune suppression, eczema/atopic dermatitis), should not be vaccinated and should stay elsewhere and avoid seeing the contact until the contact is no longer under surveillance for the development of smallpox. Unlike direct close contacts of smallpox cases, the contact’s household members are not at risk of developing smallpox unless they are exposed through the contact developing the disease while being monitored at home.

High-Risk Priority Groups for Vaccination

In addition to contacts of smallpox cases, other groups to identify for priority vaccination include:

  1. Anyone else potentially exposed to the initial virus release that doesn’t have symptoms of smallpox (vaccinate if ill but unsure of cause or if isolating patients together).
  2. Public health, medical and transportation personnel who will be potentially exposed to smallpox patients during their work activities.
  3. Laboratory personnel who would potentially handle specimens from smallpox cases.
  4. Support staff in the hospital who have exposure to the linens, clothes and waste from smallpox patients.
  5. Other groups to consider vaccinating, even though they may not have direct patient care or evaluation responsibilities would include the other response support personnel, and other essential service personnel who must be maintained at full staffing. This could include law, military and emergency workers.

Vaccine Administration Support

To vaccinated contacts and personnel, vaccination sites and procedures should be established. Establishing central designated clinic sites will minimize vaccine wastage. If personnel and vaccine supplies are adequate, it may be possible to consider the option of vaccinating contacts wherever they are located (home, work, etc.). No matter what strategy for vaccination is chosen, establishing an adverse events reporting system is important. Establishing a system to ensure all those exposed are either vaccinated or managed appropriately with isolation is also essential. 

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