UPDATE - December 2002
Graph 1: Routine immunization alone (coverage 80%)
Graph 2: Immunization campaign alone (coverage 85%)
Controlling epidemic yellow fever in Africa
Julie Jacobson, Alya Dabbagh and Gary Ginsberg explain the importance of the GAVI Board's decision last month to support the purchase of a stockpile of yellow fever vaccine
YELLOW fever (YF) is an acute, viral disease transmitted between humans by infected mosquitoes. Many infections are mild, but the disease can cause severe, lifethreatening illness. Yellow fever was almost eliminated during the 1950s through intensive vaccination campaigns, but the disease resurged in the 1980s. Now an estimated 200 000 yellow fever cases with 30 000 deaths occur each year, the majority in 33 subSaharan African countries, with over 508 million people at risk of infection.
The disease should be a simple public health problem to address---there is a safe and inexpensive vaccine and a single dose protects an individual for life. And the vaccine is effective when given to infants (at the same time as measles vaccine) or to older children and adults. But current YF vaccination efforts are not doing the job. In part this is because YF vaccine is not on the infant immunization schedule in many countries, even though the World Health Organization (WHO) recommends that atrisk countries include it. Another problem has been the lack of a sufficient stockpile of vaccine for routine use, for rapid deployment when epidemics occur, and for preventive campaigns in high risk areas. As a result, the supply of vaccine for routine use has been depleted.
When GAVI was launched in 2000, the Alliance partners agreed to provide financial support, through the Vaccine Fund, for YF vaccine for use in routine immunization programmes in endemic countries. This marked the start of a new era of YF control. However, successful control of epidemic YF requires other changes as well. Weak immunization systems and a lack of YF surveillance and diagnostics have allowed the disease to go unchecked, resulting in frequent outbreaks (such as the current epidemic in Senegal). The unpredictable nature of epidemics and a ``firefighting'' approach to their control repeatedly disrupts routine immunization services and drains human and financial resources.
Graph 3: Together, preventive campaigns
and routine coverage control YF well
An effective strategy
Through extensive review of YF disease transmission and control worldwide, WHO has established a strategy for YF prevention (see Box 1) that has proven effective in Trinidad and The Gambia. The strategy combines the use of YF vaccine in routine infant immunization with preventive campaigns.
1. WHO recommended strategies for yellow fever control
- Provide YF vaccine as part of routine infant vaccination
- Organize preventive mass immunization campaigns in highrisk districts -- both the routine and campaign coverage should reach at least 80% coverage
- Strengthen casebased surveillance, including laboratory capacity to confirm suspected cases
- Strengthen outbreak response
If YF vaccine were given only in routine immunization, it would take more than 40 years to protect the majority of the atrisk population (see Graph 1). Similarly, a single preventive campaign is insufficient: it helps initially, but soon the effect wanes as new babies are born (Graph 2). However, when used together, a single YF vaccination campaign, plus integrated use of the vaccine in routine immunization, can control epidemic YF (Graph 3). Data from Trinidad and The Gambia have demonstrated that this strategy is effective for at least 20 years, and the simple model depicted in the chart suggests that this strategy is effective for more than 40 years. It must be noted, however, that the effectiveness of this strategy is dependent on additional factors such as maintaining high routine infant immunization coverage.
At the GAVI Board meeting in November, this strategy was discussed and the Board recommended that, in addition to support for routine vaccination, the Vaccine Fund support provision of a YF vaccine stockpile for epidemic prevention and control to allow this strategy to be fully implemented. A rolling stockpile of YF vaccine is to be constituted, for use, in the worst case, in outbreak control. The remaining vaccine from the stockpile, at the end of the year, could be used to supplement existing immunization activities, in preventive campaigns in high risk areas.
Although this support will have a significant impact on reducing the death toll due to YF, the stockpile is not sufficient to vaccinate all people living in high risk areas. Efforts to raise funds from additional donors must continue so that sufficient resources are available to ensure vaccination for all high risk areas.
2. New suspected yellow fever case definition:
Any case of fever with jaundice appearing within 14 days of onset of symptoms.
Assistance from GAVI Partners
WHO and the Children's Vaccine Program at PATH (CVP/PATH) have worked in partnership with national governments and EPI programmes to reduce the burden of YF with countries in Western Africa through seven key interventions:
- Establishing an effective (casebased) surveillance system with revised case definition (see Box 2);
- Improving confirmatory diagnostic testing through developing national and subregional reference laboratories;
- Strengthening routine immunization systems;
- Ensuring a sustainable vaccine supply through increasing the global production capacity; use of the International Coordinating Group to assess requests for vaccine from the stockpile so that timely distribution is ensured in the event of outbreaks, without depleting routine supplies;
- Providing advocacy and communication support;
- Conducting training in all new areas of YF control and monitoring;
- Creating indicators to monitor a country's success in managing YF programmes (see Box 3).
3. New national/district indicators to measure progress in the YF program:
- Number of countries/districts with YF/measles coverage gap less than 5%
- Number of districts reporting and taking a blood sample from at least one case of suspected YF per year (target 80% of districts)
Significant improvements have been documented in the five countries that have received this support. For example, 80% of the supported countries in West Africa now have functioning labs and reporting systems, compared to only 20% of nonsupported countries in the same region. As a result, the supported countries reported 303 cases and confirmed 6 compared to only 34 cases reported and zero cases confirmed in nonsupported countries. These results are promising as they show that increased support and attention does make a difference.
This is only a start
To build upon the initial success of the CVP/PATHWHO collaboration with national governments, lessons must be documented and the new strategy applied in all affected countries. Vaccines provided by GAVI and the Vaccine Fund will support preventive campaigns but funding must also be identified to pay for operational costs and to assure ongoing vaccine supplies for all atrisk populations. Advocacy among partners and Ministries of Health will be essential for longterm sustainability.
Julie Jacobson, M.D., is at the Children's Vaccine Program at PATH. Alya Dabbagh, PhD, and Gary Ginsberg, PhD are at Vaccines and Biologicals, WHO.
Immunization Focus December 2002 - Contents