Read and report vaccine reactions, harassment and failures.
According to the ERVEBO package insert, efficacy of the vaccine was studied in the Ring Vaccination Study (Study 3). This study was an open-label, randomized cluster study that took place in the Republic of Guinea during the 2014 outbreak.
Each cluster was comprised of contacts and contacts of contacts of persons with laboratory-confirmed Ebola virus disease (EVD). Clusters were randomized to be given either an “immediate” vaccination or a 21-day “delayed” vaccination.
3,537 subjects ≥18 years of age were considered contacts and contacts of contacts of an index case with laboratory-confirmed EVD in the primary efficacy analysis. Of these, 2,108 were involved in 51 immediate vaccination clusters, and 1,429 were involved in 46 delayed vaccination clusters.
The median age of individuals involved in the primary efficacy analysis was 40 years. Most of the participants were male, with 70.4 percent involved in the randomized immediate cluster and 70.3 percent in the delayed clusters.
In the primary efficacy analysis, the number of laboratory-confirmed EVD cases in persons vaccinated in the immediate vaccination clusters was compared to the number of cases in persons in the delayed vaccination clusters. Cases of EVD occurring between Day 10 and Day 31 post-randomization of the cluster were included in the analysis. No cases of confirmed EVD were noted in the immediate vaccination clusters and the vaccine efficacy was determined to be 100 percent (95% CI: 63.5% to 100%). Ten confirmed cases of EVD were noted among four delayed vaccination clusters and these occurred between Day 10 and Day 31 post-randomization.
These findings, however, have been questioned by independent researchers who stated the following:
“This perfect vaccine efficacy could be true if the two groups had been comparable in all variables but the vaccination. However, the protocol of this cluster-randomised trial reveals a bias with respect to the intervention. After randomisation, people in both types of clusters (immediate and delayed vaccination) were visited by a medical study team and a surveillance team, but the medical study team did not stay in the communities of the delayed vaccination (control) clusters. People in the control clusters were only visited by the medical study team on day 0 to identify controls and obtain informed consent and then on day 21 to vaccinate the controls. By contrast, for the immediately vaccinated clusters, the medical study teams stayed in the communities to follow up the vaccinated participants with active and passive detection of side-effects. The presence or absence of a medical team attending study participants in an African community will have an effect on outcomes. Continuous interaction with the doctors and nurses of the study team for 3 weeks would have affected the knowledge and behaviour (eg, awareness of disease symptoms, keeping distance, general rules of hygiene) of the participants, which in turn would have affected disease transmission. Such changes in knowledge and behaviour are especially important when the basic reproduction number of transmission is very low, as is the case with the Ebola virus. Thus, zero cases in the immediately vaccinated clusters of this unblinded study might have been the result of other factors than the vaccine, and vaccine efficacy might have been lower than 100%. All possible cases of Ebola virus disease might have been averted by behavioural change; in such case, the vaccine efficacy would have been 0%.”
The researchers also warned that inaccurate vaccine efficacy data might have serious and potentially fatal consequences if vaccinated individuals did not follow stringent infection control measures because they assumed complete protection from vaccination.
A March 2020 study on 257 patients admitted to the Ebola Treatment Units (ETU) in the Eastern Democratic Republic of the Congo (DRC) reported that vaccinated individuals had a higher survival rate. In this study, 44 of the 257 patients had been vaccinated but were admitted for treatment of Ebola. Study authors noted that vaccinated individuals had lower viral levels and were less likely to suffer from kidney injury, but also reported that 23 percent (10/44) died of the disease.
The measure of immune response that is indicative of protection against EVD is unknown. Additionally, persons who receive ERVEBO could have an immune response that might prevent laboratory tests from differentiating between wild-type and vaccine-strain Ebola infection. The ERVEBO package insert reports that “the vaccine virus RNA has been detected by RT-PCR in blood, saliva, urine, and fluid from skin vesicles of vaccinated adults” and that “transmission of vaccine virus is a theoretical possibility.” This means that the vaccine has the potential to infect others with vaccine-strain Ebolavirus due to virus shedding.