The immunogenicity generated by 3 experimental Ebola vaccines appears to be long-lasting, as it has persisted for at least 2.5 years, according to data presented at the Annual Meeting of the American Society of Tropical Medicine and Hygiene held October 28-November 1, 2018 in New Orleans, Louisiana.
Of the vaccines developed following the 2014-2016 Ebola outbreak in West Africa, early stage clinical trials showed that 3 candidates that encoded the Zaire Ebola glycoprotein demonstrated acceptable reactogenicity and promising immunogenicity. One vaccine candidate was a single-dose approach based on a replicating vesicular-stomatitis virus (rVSV ZEBOV) and the two others were heterologous prime-boost combinations using replication-deficient adenoviruses (ChAd3 and AdHu26) to prime and the multivalent MVA BN-Filo to boost. Although the rVSV ZEBOV vaccine showed 100% short-term efficacy in a phase 3 ring vaccination trial after exposure to Ebola virus disease cases, durability has not yet been evaluated.
Clinical trials of both prime-boost regimes have been followed up to determine the durability of both humoral and cellular immunity, and the results show that 91% of 43 recipients of the AdHu26/MVA vector vaccine had positive glycoprotein-specific IgG titers at 2.5 years post-immunization, as did 54% of 13 recipients of Chad3/MVA vectored vaccines. In addition, rVSV ZEBOV was administered in 2015 to 26 contacts of a healthcare worker infected with Ebola virus in Sierra Leone, who recovered and then subsequently relapsed. Samples from this cohort will allow for comparison of immunogenicity using a standardized enzyme-linked immunosorbent assay (ELISA) and validated enzyme-linked immunospot (ELISPOT) assay to determine humoral and cellular immunity against the Zaire Ebola virus glycoprotein. In addition, samples that were obtained 2.5 years post-vaccination will also be compared to determine whether there are differences in quality, quantity, and persistence of immunity.
“These data are important for long-term strategic planning for prophylactic protection of front-line healthcare workers in regions at risk of future outbreaks,” concluded the investigators.
Ewer K, Smith C, Sarlar E, at al. Durability of immune responses induced by three leading candidate Ebola vaccine regimes; rVSV ZEBOV, ChAd3 EBO Z-MVA BN-Fila an dAdHu26.ZEBOV-MVA BN Filo. Presented at: ASTMH Annual Meeting; October 28-November 1, 2018; New Orleans, Louisiana. Abstract 685.