Ebola is racing through the eastern part of the Democratic Republic of the Congo (DRC), outpacing urgent efforts to halt it. Bundibugyo virus, the rare Ebola strain responsible for the outbreak, has no approved vaccine or treatment, and it’s fatal in about half of cases. This places a heavy burden on the DRC’s health care system, which is weakened by armed conflict, severe international funding cuts, mass displacement, and other disease outbreaks.

Given the outbreak’s urgency, researchers and health officials have begun evaluating how vaccines designed for other Ebola strains, assumed to provide partial protection, could influence outcomes. At the same time, safety testing is beginning for new, Bundibugyo-specific vaccine candidates.

As the World Health Organization begins sending doses of the existing Ervebo vaccine to the DRC, Stanford Medicine-led research in The Lancet Infectious Diseases sheds important light on the vaccine’s potential to contain the outbreak. Researchers led by infectious disease professor Jason Andrews, MD, modeled vaccines of varying effectiveness alongside other prevention strategies. Assuming 45% protection against Bundibugyo, the study found that a vaccine like Ervebo could contain transmission and save lives when deployed broadly and rapidly, but the approach is resource-intensive and time-sensitive.

The findings emphasize the importance of increased international support for contact tracing, containment, and diagnostics alongside vaccine access, Andrews said.

“Having more resources poured into this response is critical because we are so far behind where we need to be,” he said.

Andrews, a global health faculty fellow at the Stanford Center for Innovation in Global Health, discussed his findings and their implications for the outbreak response as well as for future global health threats.

What concerns you most about the current outbreak in the DRC?

This is the second deadliest Ebola virus outbreak in history after the 2014 West Africa outbreak, and the deadliest in the DRC’s history. It’s also the most rapidly spreading, with cases growing both numerically and geographically. A major concern is under-detection: We may be capturing only about a third of cases and deaths, meaning reported totals (more than 6,186 cases and 3,007 deaths as of Sept. 2) likely represent only the tip of the iceberg.

What prompted this study, and what do you hope it will contribute?

This study arose from my lab’s focus on global infectious diseases affecting vulnerable populations. We look for scientific problems where our skills, including the modeling strategies employed here, can identify more effective solutions.

Watching this outbreak unfold, we recognized important questions about how to respond. We asked, “If we deploy a vaccine like Ervebo that offers partial rather than full protection, what impact would we see, and which strategies would be most effective?” This mattered because when my colleague Isaac Bogoch [MD, an infectious disease professor] at the University of Toronto and I began this work in May, the WHO was deciding whether and how to use this vaccine against the Bundibugyo outbreak.

We’ll continue to have emerging infections …and we have the technologies to develop effective tools and mechanisms for responding to them.

Jason AndrewsProfessor of Medicine – Infectious Diseases

As we prepared to publish these findings, encouraging data on Ervebo emerged suggesting partial protection. We were glad we could share our findings in August with the WHO’s analytics working group, which is advising on the response and the use of this vaccine.

Based on your findings, what are the best preventive measures that can be taken in this outbreak?

Our findings affirm a core convention of public health: Finding cases and isolating them are the most important ways to stop Ebola’s spread. In this case, unfortunately, that’s easier said than done. Responders lack the resources to keep pace with the thousands of new contacts occurring every day and face immense challenges related to the conflict, food insecurity, and displacement currently happening in the DRC.

Given these challenges, what is the role of a partially effective vaccine, as Ervebo is thought to be? And if a more effective vaccine is developed, how would that change things?

We saw limited benefit using the WHO’s core vaccination strategy of ring vaccination [immunizing close contacts of confirmed or suspected cases]. This method depends on finding contacts quickly, which is very difficult when about two-thirds of new cases are in people not on exposed contact lists. This motivated us to evaluate community-wide vaccination, which would be more effective but requires robust infrastructure and millions of doses that are not currently available.

In light of these constraints, a layered response remains essential. Even with a highly effective vaccine, we found that case finding, isolation, and contact tracing were foundational and drove the largest mortality reductions on their own.

What are the most effective strategies to pursue, given constrained resources?

In this case, we can’t settle for doing the best we can with the resources we have. The DRC simply needs more resources. This is a serious global health emergency that has already led to cases in Uganda and France, and prior Ebola outbreaks have spread across borders as well. The devastation in the DRC is bad enough, but I hope that the threat to global security provides extra impetus for countries to step up and invest.

What can the Bundibugyo outbreak, along with your recent modeling of transmission dynamics for the Andes virus (hantavirus) outbreak on a cruise ship earlier this year, teach us about preparing for emerging threats when no vaccine exists?

First, we need to invest in scientific research to understand these viruses. With Andes virus, very little research exists on the basics of transmission, and we have no vaccine. Yet with the proper investments, we’ve shown that we can successfully deliver vaccines for emerging pathogens, as was done with the Zaire species of Ebola.

Second, we need to anticipate future outbreaks and invest in the platforms to combat them. We’ll continue to have emerging infections every year – usually from animal spillovers – and we have the technologies to develop effective tools and mechanisms for responding to them.

Finally, we need stronger investments in public health responses more broadly. The current Ebola outbreak is a devastating emergency, but it isn’t unexpected, nor is it occurring in isolation. We will continue to see outbreaks of emerging infections, and we must be better resourced to contain them and mitigate their impacts.