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:
- No known
cases of smallpox at this time.
- It is unclear
if there are individuals, groups, or governments that have smallpox
for use as a weapon.
- Since regular
vaccination with smallpox was stopped worldwide over 20 years
ago, there are entire populations who are vulnerable to infection
with smallpox virus.
- 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).
- 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:
- 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).
- Public health,
medical and transportation personnel who will be potentially
exposed to smallpox patients during their work activities.
- Laboratory
personnel who would potentially handle specimens from smallpox
cases.
- Support staff
in the hospital who have exposure to the linens, clothes and
waste from smallpox patients.
- 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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