Study Affirms Effectiveness of Vaccination "Ring" Around Ebola
Promptly vaccinating the "ring" of contacts and contacts-of-contacts along with standard infection control measures interrupted Ebola transmission in the DRC.
Jean-Jacques Muyembe, PhD, director, Institut National de Recherche Biomédicale (INRB), and codiscoverer of the Ebola virus.
Promptly vaccinating the "ring" of contacts and contacts-of-contacts of persons contracting Ebola, in conjunction with standard infection control measures, was found to reduce emergence of cases within 10 days of vaccination, in a study1 of time-response to the strategy in the 2018-2020 outbreak in the Democratic Republic of Congo (DRC).
The study with the single-dose, live-replicating rVSVΔG-ZEBOV-GP vaccine (Ervebo) reinforces earlier findings2 from the 2014-2016 outbreak in Guineathat the ring vaccination strategy, used successfully in eradicating small pox a half century earlier, in conjunction with standard infection control measures is more effective immediately after an active case is identified than when delayed until after control measures are in place or a population-wide program can be implemented.
In the DRC study, investigators distinguished the emergence of Ebola virus disease (EVD) between rings of vaccination accomplished within 0 to 9 days (380 cases) or 10 to 20 days (32 cases) after identifying and isolating an infected person. 1,853 rings of vaccination were established around new cases or clusters within 21 days after symptom onset in the index case.A total of 265,183 participants were vaccinated during the outbreak, of which 102,515 were monitored on days 0, 3, and 21 for safety.
The investigators reported that the sooner the infection control measures, including vaccination, was implemented after the index case was identified and isolated, the sooner EVD rates decreased among vaccinated contacts.In each subgroup, EVD rates fell suddenly around day 10 after vaccination.
Among contacts and contacts-of-contacts who were uninfected at day 10, the EVD onset rate during days 10 to 29 was 0.16/1000.The investigators contrast this to the rate of 4.64/1000 that had occurred in Guinea in the group that was subject to immediate control measures but a delay in vaccination until day 21 after identifying the ring of contacts.
Jean-Jacques Muyembe, PhD, on Combating Ebola
The lead author of the DRC study is Jean-Jacques Muyembe, PhD, director of the Institut National de Recherche Biomédicale (INRB) and codiscoverer of the Ebola virus. Muyembe discussed the study with Contagion, remarking on the many challenges that were encountered in the DRC campaign against EVD, including the vaccine hesitancy that confounds public health efforts across the globe.
"Vaccine hesitancy was a challenge due to misinformation, fear of outside agendas, and cultural barriers," Muyembe said. "To address this, we worked with local healthcare workers, community leaders, and trusted influencers to explain the vaccine's safety and importance. Their involvement helped ensure the message resonated with communities."
Control measures were implemented by teams charged with four key tasks, Muyembe explained:
- Defining the ring—listing contacts and contacts-of-contacts from the case data provided by the DRC Ministry of Health and the WHO surveillance teams
- Obtaining informed consent—ensuring vaccine recipients understood and agreed to vaccination
- Vaccine administration—delivering the vaccine
- Safety follow-up—Monitoring vaccines post-vaccination
"All team members were trained in good clinical practices, the study protocol, and the standard operating procedures for ring vaccination," Muyembe said."Surveillance teams focused on identifying cases and tracing contacts, often with support from community members. Laboratory teams tested suspected cases to confirm or rule out Ebola.
"In areas with security concerns, military or UN peacekeepers provided protection for vaccination teams, but did not engage with the communities directly, preserving trust in the health workers," Muyembe noted.
With the study confirming the importance of prompt ring vaccination, Muyembe described the efforts to hasten recognition and reporting of an Ebola infection."Early detection is critical for the success of the ring vaccination strategy and the outbreak response as a whole," he declared.
"We accelerated case recognition through public health campaigns that educated communities on Ebola symptoms and encouraged timely reporting. Community health workers played a vital role by linking suspected cases to response teams using hotlines and other communication tools. These efforts reduced delays in identifying and isolating cases," Muyembe recounted.
