Do Ebola vaccines protect nonhuman primates against aerosolized virus challenge?

The short version: yes, the evidence shows that at least one Ebola vaccine platform protects nonhuman primates against aerosolized virus challenge, but the data is very thin.

The only study that directly answers this question is a 2008 experiment using a vesicular stomatitis virus (VSV)-based vaccine [1]. Cynomolgus macaques were vaccinated intramuscularly with a VSV vector expressing either the Zaire Ebola virus glycoprotein (GP) or the Marburg virus GP. Three weeks later, they were challenged with a lethal aerosol dose of the homologous virus. All vaccinated animals survived with no detectable virus in their blood or swabs, while all unvaccinated controls died within days [1]. This is a clean result: a small group (3-4 vaccinated per virus), but the outcome was complete protection.

The study also tested a Marburg virus challenge with the same design and got the same result: 4 out of 4 vaccinated animals survived, 2 out of 2 controls died [1]. The protection was sterilizing in the sense that no virus was detected after challenge, but the sample sizes are tiny. The study was published in a peer-reviewed journal, but the funding source is not stated in the retrieved record. The immune mechanism was not fully characterized: the animals had modest GP-specific IgG titers before challenge, but no detectable T-cell responses were measured [1].

The rest of the retrieved evidence does not address aerosol challenge. Several studies show that VSV-vectored Ebola vaccines protect nonhuman primates against intramuscular or intraperitoneal challenge [2, 3, 4], but aerosol is a different route. The 2008 study is the only one that used an aerosol challenge, and it has not been replicated in a larger group or with a different vaccine platform. The evidence is consistent with the claim that a VSV-based vaccine can protect against aerosolized Ebola in nonhuman primates, but the data comes from a single, small study.

My call: the evidence supports that a VSV-vectored Ebola vaccine can protect nonhuman primates against aerosolized challenge, but the evidence base is a single small study from 2008 with no replication. Confidence: moderate for the specific vaccine and species tested, low for generalizing to other vaccines or to humans.