Use of Ebola Vaccines — Worldwide, 2021–2023

Discussion

The ICG stockpile provides equitable access to vaccines that can be shipped quickly in the event of an Ebola outbreak. The relatively small number of doses used for outbreak response (6,570; 5% of doses shipped) reflects the smaller size and rapid containment of Ebola outbreaks since 2021. North Kivu, DRC, has received and administered more doses than any other geographic area worldwide since 2018, which might have contributed to the rapid containment of subsequent outbreaks in that area (1).

After approvals of vaccine for preventive use by ICG in 2022, WHO, in early 2023, circulated an internal memo on behalf of ICG informing at-risk countries of the availability of vaccines for preventive vaccination of health care workers and frontline workers. Preventive vaccination campaigns have targeted health care workers and frontline workers in at-risk countries, given their increased risk for exposure because of their frequent contact with patients (8). The addition of preventive Ebola vaccination of these workers could reduce total cases, hospitalizations, and deaths in Ebola outbreaks by an estimated 14%–38% compared with nonpharmaceutical interventions and ring vaccination alone (8).

The variability of Ebola outbreak size and time to containment makes predicting future vaccine needs challenging. Repurposing doses for preventive vaccination of targeted groups can protect high-risk persons as well as make use of doses with a shorter shelf life. More than 200,000 short–shelf-life doses in the ICG stockpile due to expire in 2024 could be redirected for preventive vaccination. In addition to focusing on reactive (outbreak response) vaccination, early planning for preventive vaccination with short–shelf-life doses could be incorporated into future stockpile management strategies. Additional studies accounting for the variability in outbreak size could guide planning to maximize the cost-efficiency of stockpile management.

The frequency of recent outbreaks, especially those linked to viral persistence, highlights the need for innovative strategies to protect Ebola survivors and prevent reintroductions. One such strategy is to offer postoutbreak immunization to close contacts of survivors, including new sex partners and other groups at risk for transmission because of viral persistence (9). Additional avenues to expand preventive vaccination among high-risk populations could be explored in countries at risk for outbreaks. Demand-generation activities** incorporating findings from community engagement and vaccine acceptance studies in targeted risk groups could accompany vaccination campaigns and help develop targeted engagement plans. Investments and advocacy for preventive vaccination against Ebola are crucial for health system preparedness and resiliency. Currently, Gavi, WHO, and UNICEF are coordinating with other partners to develop a learning agenda^†† to help guide research prioritization and funding decisions for Ebola vaccine use.

Limitations

The findings in this report are subject to at least two limitations. First, whereas the Ebola vaccine has reduced morbidity and mortality during outbreaks, the impact of Ebola vaccines on preventing outbreaks is difficult to ascertain because of the infrequent occurrence of the disease. Second, important data are lacking regarding the duration of protection, vaccine effectiveness in outbreak situations, and the need for booster doses. These data will be needed to guide decision-making regarding vaccination strategies and should be a focus for future research.

Implications for Public Health Practice

The availability of licensed Ebola vaccines is an important advancement in Ebola prevention and global health security. In the absence of large-scale outbreaks, the demand for vaccines lags behind the current supply of doses, and preventive vaccination could be considered for high-risk groups. Investments, advocacy, and additional research to inform preventive vaccination are crucial for health system preparedness and resiliency. Focus on working with countries at risk for Ebola outbreaks to identify high-risk groups and generate demand for preventive vaccination is important for optimizing the use of the stockpile. Ensuring the availability of sufficient Ebola vaccine doses for emergency outbreak response remains the priority of ICG.