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 of 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 considers the available human, logistical and financial resources that can be mobilised effectively.

The most appropriate approach is determined based on analysis of the potential for spread (see Chapter 3, Table 3.2).

Table 4.2 - Response according to the potential for spread of the outbreak (See also Section 4.4.5)

4.4.1 Stepping up routine vaccination activities

As soon as an outbreak is suspected, check if routine vaccination activities are working properly 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/adherence) 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 outreach strategies.

Increasing resources

• Ensure the availability of vaccines and injection supplies
• Consider catch-up vaccination for measles, and if possible for all diseases, up to age 5 years
• Offer logistical support (cold chain, transportation, fuel)
• Provide ad hoc human resource reinforcement (additional staff assigned to vaccination during the period) and boost health promotion and community engagement, if needed

4.4.2 Mass vaccination campaign [1]Citation 1.Gignoux E, Polonsky J, Ciglenecki I, et al. Risk factors for measles mortality and the importance of decentralized case management during an unusually large measles epidemic in eastern Democratic Republic of Congo in 2013. Arez AP, ed. PLOS ONE. 2018;13(3):e0194276. doi:10.1371/journal.pone.0194276

The objective of the campaign is to limit the number of cases and deaths and to contain the outbreak by vaccinating 100% of the target population.

Whenever possible, to limit the spread and number of cases, begin with densely populated zones (urban areas and refugee/IDP camps), because this allows rapid protection in the zones at highest risk of rapid spread. Access, logistics and supervision are also easier in these areas. To reduce the number of deaths, also consider areas with very limited access to care.

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 care for patients with measles or other diseases. 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
    For example: smaller schools should bring their children to the vaccination sites set up in larger schools during the least busy times, or by appointment
  • In other group settings: day care centres, nursery schools, orphanages, juvenile detention centres, etc.
  • In places where people gather (markets, food or mosquito net distribution sites, 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. ethnic groups)
• 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:

• Vaccinating in existing health care facilities
• Sending mobile teams into areas that are far away from health centres. This is the most appropriate option for reaching “zero-dose children”, who do not have access to routine vaccination (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 geographic areas and age groups to be targeted first.

Priority areas

• Particularly high-risk facilities: paediatric inpatient units, feeding centres, facilities for young children (childcare centres, schools, orphanages, etc.)
• Densely populated geographic areas (cities, slums, refugee/displaced people camps)
• Geographic areas with the highest attack rates, considering the shape of the epidemic curve
• Geographic 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 MJ, Djibo A, Grais RF, Grenfell BT, Bjørnstad ON. Episodic outbreaks bias estimates of age-specific force of infection: a corrected method using measles as an example. Epidemiol Infect. 2009;138(1):108-116  doi.10.1017/S0950268808001927 , on the objectives (reducing the morbidity and mortality), and the amount of resources to be mobilised. When the resources are available, a vaccination campaign that vaccinates a broader age range (up to age 15 years) can halt the spread of an outbreak more effectively. However, the younger age groups (under 5 years) are still at highest risk of death and are often efficient spreaders of the disease. Interventions should therefore consider context-specific constraints when organising a campaign.  
 

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 to 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

Definition:

• Selective vaccination: routine check of the child’s vaccination status based on the vaccination card. If two-dose 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.

Choice of vaccine

In countries whose immunisation schedule includes the measles-rubella vaccine, the measles-rubella vaccine is used for all outbreak response campaigns against measles outbreaks, rubella outbreaks, and mixed measles-rubella outbreaks.

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), and will help reduce mortality.

Find out about distributions that have already been done or are planned.

• 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 (8 drops from a 200,000 IU capsule) 

Other activities

• Other vaccinations:
  The existence of a measles outbreak is a sign that measles vaccination coverage is inadequate. The vaccination coverage for other diseases is often similar. All outbreak response vaccination campaigns should therefore be considered an opportunity to vaccinate against multiple diseases. This is particularly justified:

  • When there is another outbreak happening (meningitis, yellow fever, polio, etc.) at the same time
  • In some specific situations (refugee camps, population displacement)
  • In areas with very low vaccination coverage (difficult access, marginalised population)
     

  All other vaccinations require appropriate adjustments to the public messaging, vaccine resources, cold chain, personnel, data collection tools and circuit (Appendix 48) and staff training.

  
  The decision to add other vaccines must take the context and available resources (vaccine stocks, cold chain capacity, personnel, financial resources, etc.) into account to avoid delaying the outbreak response campaign.

• Other activities:
  Other activities may be conducted during vaccination campaigns, such as vitamin A, deworming, malaria chemoprophylaxis, and distribution of insecticide-treated mosquito nets or nutritional supplements.
   

Always weigh the potential benefits of additional activities against the implementation constraints (including the delay in achieving effective vaccination coverage) they entail, and make sure they do not delay the outbreak response vaccination campaign.