It has been nearly one month since the Democratic Republic of the Congo (DRC) declared a new outbreak of the Ebola virus. As of June 2, the World Health Organization (WHO) reported 53 confirmed, probable, and suspected cases, including 25 deaths, in the northwestern Équateur Province. The outbreak, which was officially declared on May 8, marks the country’s ninth encounter with the deadly virus since its discovery along the Ebola River in 1976.

Significantly, the entrance of Ebola into the densely populated city of Mbandaka along the Congo River has prompted comparisons to the catastrophic West Africa Ebola epidemic of 2014-16, which also entered urban areas. That outbreak ultimately infected 28,616 people and caused 11,310 deaths in the main affected countries of Liberia, Guinea, and Sierra Leone. It also required a massive international effort to contain it, including the creation of the UN’s first-ever emergency health mission.

So far in the DRC, fortunately, the combination of faster outbreak detection by national authorities, a swift response by international and NGO partners, and the use of new countermeasures have averted the “explosive increase” in cases initially feared by the WHO. This progress may be partially attributed to the use of an experimental Ebola vaccine, which has been administered to 680 contacts in the outbreak zone since officials began a ring vaccination campaign on May 21. While the vaccine is proving to be a key element of the response, it is not a silver bullet, and challenges have surfaced to operationalizing the vaccine on the ground.

Echoes of West Africa?

As I have written elsewhere, early signs indicated the potential for the outbreak to rapidly escalate, as occurred during the initial stage of the 2014 Ebola outbreak in West Africa. Memories of the West Africa crisis no doubt weigh heavily on the minds of public health officials, including WHO Director-General Tedros Adhanom Ghebreyesus, who visited the affected town of Bikoro on May 13. Tedros convened a WHO emergency committee meeting on May 18, which determined that the situation did not yet warrant declaring a “Public Health Emergency of International Concern.”

Unlike the pattern of past outbreaks in DRC, which have largely been confined to remote areas, Ebola has been reported in the port city of Mbandaka—home to approximately 1.2 million residents. Close quarters of this kind can facilitate rapid spread, since the virus is transmitted primarily by direct contact via exchange of blood and other bodily fluids from symptomatic individuals. In the case of Ebola, this typically occurs in healthcare settings or during burial rites. Similarly, urban transmission was a key driver of the West Africa epidemic during the summer of 2014, demonstrating “how swiftly the virus could move once it reached urban settings and densely populated slums.”

The geography of the outbreak is equally concerning. Mbandaka’s proximity to the Congo River—referred to elsewhere as the Ebola “superhighway” because it is used as a major transport route—could allow the virus to spread to nearby cities and countries. The Congo River acts as a porous border between the DRC and the Republic of Congo to the west, and it also provides access to the Central African Republic to the north. Likewise, the first reported Ebola cases in West Africa occurred in Guinea’s southeastern forest region, located only a few kilometers from the borders of Liberia and Sierra Leone. Given limited cross-border controls, it did not take long for cases to surface 400 kilometers away in Monrovia.

Given the similarities between the two outbreaks, what explains their markedly different outcomes, even in these early stages? Compared to West African countries, the DRC has benefited from faster detection, likely due to higher clinical suspicion among Congolese health workers trained to look for signs of Ebola; a swift response by the WHO, which has dispatched medical experts and supplies to the region, backed by $12 million in emergency funds from the World Bank’s Pandemic Emergency Financing Facility; and the deployment of experimental countermeasures to the outbreak zone.

Collectively, these activities indicate a higher level of preparation, speed, and coordination among international and local partners than during the outbreak response in West Africa.

Vaccination Challenges

As mentioned, the Ebola outbreak in DRC is notable for the use of an experimental Ebola vaccine, called rVSV-ZEBOV. The development of rVSV-ZEBOV represents the culmination of a major international effort among myriad actors in global health, including national governments, pharmaceutical companies, the WHO, international NGOs, including Médecins Sans Frontières (MSF), and public-private partnerships, including Gavi, the vaccine alliance. Developed by Canadian researchers and licensed to American pharmaceutical company Merck, the vaccine was shown during a ring trial in Guinea in 2015 to offer high levels of protection against the disease.

Yet, the existence of a vaccine alone is not sufficient to stop the outbreak, as evidenced by a large, ongoing outbreak of yellow fever in Brazil and other settings where vaccine technology has existed for decades. Numerous challenges exist in connection with vaccine storage, transport, delivery, and administration. For example, the vaccine must be stored and transported in freezing temperatures to ensure its viability. The WHO has circumvented this logistical hurdle by utilizing cutting-edge technology to maintain the cold chain in the remote Equateur Province.

In addition, public health authorities will need to educate affected communities about the vaccine’s risks and benefits. This is especially true since the current formulation is experimental, with high potential for unknown adverse events. Furthermore, evidence provided by MSF suggests some confusion among affected communities, with individuals reportedly refusing hospital care because of expectations that the vaccine will cure them. Others falsely believe they will receive the vaccine even though they have not been identified as priority candidates. Combined with troubling reports that Ebola patients “escaped” an isolation unit at a hospital in Mbandaka, these experiences suggest greater effort is needed to sensitize the public about the dangers of the disease and the role of the vaccine in the overall response.

Finally, the importance of implementing tried-and-true approaches, such as isolation and treatment of patients and contact tracing, should not be forgotten amid the overarching discussion of vaccine efficacy. The concern is that overreliance on the vaccine will cause officials to “let their guard down,” according to one infectious disease specialist. If this temptation can be avoided, there is reason to be optimistic that the outbreak can soon be controlled.