4.4 Choosing the outbreak response vaccination strategy

Outbreak response vaccination is defined based on several factors: identification of at-risk priority zones, a target population and coverage objectives.

 

Though there is often a lot debate and pressure over the choice of zones to vaccinate and the strategy (mass vaccination and/or stepped-up routine vaccination), decisions need to be made quickly. The choice takes into account the available human, logistical and financial resources that can be mobilised effectively [1] Citation 1. World Health Organization. Response to measles outbreaks in measles mortality reduction settings. CH-1211 Geneva 27, Switzerland. WHO/IVB/09.03
http://apps.who.int/iris/bitstream/handle/10665/70047/WHO_IVB_09.03_eng.pdf?sequence=1 .

 

The most appropriate approach is determined based on analysis of the potential for spread.

 

Table 4.2: Response according to the potential for spread of the outbreak

 

 

4.4.1 Stepping up routine vaccination activities

As soon as an outbreak is suspected, make sure that routine vaccination activities are operating correctly and are effective.

 

In the absence of vaccination coverage survey data, an analysis of routine vaccination data helps identify pockets of low coverage. Identifying the reasons for non-vaccination in these zones permits an understanding of the perception of and barriers to vaccination and the implementation of appropriate response strategies.

Informing and mobilising the public

Awareness-raising messages must consider the population’s perception of vaccination (acceptability/resistance) and its knowledge (population accustomed or not to routine vaccination). Consider previous experiences.
All effective channels of communication should be used.

Improving access

• Routinely check immunisation status in all activities (curative and preventive), including accompanying children.
• Hold daily vaccination sessions with extended hours.
• Increase the frequency of mobile team rounds or step-up other forward operating strategies.

Increasing resources

• Ensure the availability of vaccines and injection supplies.
• Offer logistical support (cold chain, transportation, fuel).
• Provide ad hoc human resource reinforcement (additional staff assigned to vaccination during the period).

4.4.2 Mass vaccination campaign

The objective of the campaign is to limit the number of cases and deaths and to contain the outbreak by vaccinating at least 90% of the target population.

 

Whenever possible, begin with densely populated zones (urban areas and refugee/IDP camps), because that allows rapid protection in the zones at highest risk and where accessibility, logistics and supervision are easier.

 

The proposed vaccination hours should take the population’s activities and work schedule into account.

Urban and densely-populated areas

In urban areas, it is better not to involve the health care facilities in the vaccination campaign. The work overload could compromise patient care. Special, temporary vaccination sites should be set up. To be accessible to everyone, the vaccination sites should be distributed among the various neighbourhoods according to the size of their populations.

 

At the end of the campaign, maintain vaccination sites in the health care facilities for at least one week to vaccinate latecomers.

 

Other approaches are combined with setting up vaccination sites:

• Mobile vaccination teams:
  • in school settings: primary and secondary or high schools where many children go to school.
    The smaller schools should bring their children to the vaccination sites at the larger schools during the least busy times, or by appointment, for example;
  • in other group settings: day care centres, nursery schools, orphanages, juvenile detention centres, etc.;
  • for populations living far from health centres or in remote areas (e.g., nomads);
  • for groups that do not like to mix with other groups (e.g., castes).
• Other approaches: consider any alternative approach that allows vaccination of groups identified as having low vaccination coverage (e.g., door-to-door).

Rural areas

In rural areas, the response is a combination of several vaccination strategies:

• ad hoc reinforcement of vaccination capacity for existing care facilities: contribution of human, technical or logistical resources;
• sending mobile teams into areas that are far away from health centres. This is the most appropriate option for reaching populations without access to care (nomads or dispersed groups).

 

These mobile teams are smaller than those in urban areas. The teams can stay one or more days in selected locations, serving several localities, if possible. Failing that, they can travel among the localities to be vaccinated using a predefined circuit, provided the population has been informed ahead of time.

 

Achieving effective vaccination coverage rates requires significant logistical resources and a longer campaign than in urban areas. Supervision is also much more complex.

4.4.3 Identifying the target population

Calculating location- and age-specific attack rates allows identification of the geographicareas and age groups to be targeted first.

Priority areas

• Particularly high-risk areas: paediatric inpatient units, feeding centres, facilities for young children (child care centres, schools, orphanages, etc.)
• Densely-populated areas (cities, slums, refugee camps, displaced population)
• Areas with the highest attack rates, taking into account the shape of the epidemic curve
• Areas with low vaccination coverage

At-risk groups

The choice of the target population depends on the attack rate and the absolute number of cases in each age group [2] Citation 2. Ferrari M. J., Djibo A., Grais R. F., Grenfell B. T., Bjørnstad O. N. Episodic outbreaks bias estimates of age-specific force of infection: a corrected method using measles as an example. Epidemiology and Infection / Volume 138 / Issue 01 / January 2010, pp 108-116 , on the objectives (reducing the morbidity and mortality), and on the amount of resources to be mobilised.

 

Be careful when interpreting the attack rate; for example, though the attack rate for 5- to 15-year-olds may be lower than that for children under 5, it may actually correspond to more cases, because 5- to 15-year-olds represent a larger percentage of the total population.

4.4.4 Evaluating the constraints

When planning a vaccination campaign, take the following constraints into account:

• the supply time for vaccines and supplies;
• logistical capacity: when limited, it is better to start the campaign quickly, targeting the priority zones, than wait for the means for a larger scale operation that will be too late. This allows time to mobilise the means for vaccinating in other zones;
• available personnel;
• accessibility: road network, distance, population density;
• special events (holidays, elections, food distribution, etc.);
• security.

 

 

4.4.5 Other points to be determined

Selective or non-selective vaccination

• Selective vaccination: routine check of the child’s vaccination status based on the vaccination card. If vaccination is proven (the card is shown), the vaccine is not administered.
• Non-selective vaccination: all children are vaccinated, no matter what their vaccination history (cards not checked).

 

Non-selective vaccination, which is faster, is the preferred option in outbreak response vaccination campaigns. The choice should be made as soon as planning begins, as it will have an impact on the resources to be deployed and activity organisation.

Vitamin A distribution

Preventive doses of vitamin A (oral retinol) are distributed at all measles mass vaccination campaigns (except in cases of recent administration, i.e., within the past month).

Inquire about previous or planned vitamin A distributions.

• Children 6 to 11 months: 100,000 IU single dose (4 drops from a 200,000 IU capsule)
• Children 1 to 5 years: 200,000 IU single dose (one capsule)

Other activities

• Other vaccinations:

While it is possible to add other vaccines, it must be justified. This might be considered when there is another epidemic occurring at the same time (e.g., meningitis, yellow fever, polio) or in certain special situations (e.g., refugee camps, population displacements, or remote areas with very low polio, pneumococcus, Haemophilus influenzae (Hib) or yellow fever vaccination coverage).

 

• Other activities:

Other activities may be conducted during vaccination campaigns, such as deworming, or distribution of insecticide-treated mosquito nets or nutritional supplements.

 

The organisation of the vaccination flow will have to be adapted, the duration of the campaign extended, and the personnel given specific training. Always weigh the potential benefits of additional activities against the implementation constraints (including the delay in achieving effective vaccination coverage) they entail.