Peri-exposure protection against Nipah virus disease using a single-dose recombinant vesicular stomatitis virus-based vaccine

Abstract

Nipah virus is a zoonotic paramyxovirus that causes severe disease in humans and animals. Due to almost yearly outbreaks in Bangladesh, and a large outbreak in Malaysia that lead to the shutdown of swine export, Nipah virus is both a threat to public health and the economy. Infection is associated with respiratory distress, encephalitis and human-to-human transmission, resulting in high case fatality rates during outbreaks. This study aims to address the amount of time needed until protection from a recombinant vesicular stomatitis virus-based vaccine candidate expressing the Nipah virus glycoprotein (G), which we have previously shown to protect hamsters and non-human primates when administered 28 days before challenge. We found that a single-dose vaccination, when administered 1 day before challenge, reduced viral load, limited pathology and fully protected hamsters from Nipah virus infection. The vaccine was even partially protective when administered at early time points following challenge with Nipah virus. These data indicate that a single administration of this vaccine to high-risk individuals, such as family members and health-care workers of infected patients, could be protective and useful for reducing human-to-human transmission and curbing an outbreak.

Figure 1

Survival of vaccinated hamsters following Nipah virus challenge. Groups of six hamsters were vaccinated intraperitoneally with 10⁵ plaque-forming units of the designated vaccine; (a) DMEM control, (b) rVSV-EBOV-GP and (c) rVSV-EBOV-GP-NiV-G. Individual vaccines were administered at the indicated time points relative to challenge. Hamsters were challenged with 1,000 LD₅₀ of Nipah virus—Malaysia and monitored for disease for 42 days.

Figure 2

Antibody titres to Nipah virus in hamsters after challenge. Sera were collected from hamsters at 42 d.p.i. and a Nipah virus-specific enzyme-linked immunosorbant assay was performed. (a) Survivors vaccinated with rVSV-EBOV-GP vector control and (b) survivors vaccinated with rVSV-EBOV-GP-NiV-G. Colours represent the time of vaccination and data are shown as an average of all animals in a particular group that remained at 42 d.p.i. The negative control is non-infected hamster serum and the positive control serum was from a Nipah-infected hamster.

Figure 3

Decreased viral load in tissues is associated with survival. Tissues (lung—left column, spleen—middle column and brain—right column) from four animals per group were collected 5 days after challenge. Tissues were homogenised and total RNA was extracted. TCID₅₀ equivalents were determined by quantitative reverse transcription PCR using an N gene-specific primer and probe set with a standard of known TCID₅₀ equivalents. Individual animals from each vaccination group (DMEM—top row, rVSV-EBOV-GP—middle row and rVSV-EBOV-GP-NiV-G—bottom row) are represented by individual dots, bars represent the mean of each group and error bars indicate s.e.m. Groups of animals that were protected by vaccination in the survival experiment are designated by (+), partially protected by (±) and groups not protected by (−). One-way analysis of variance with Tukey’s post tests was performed on each vaccination time point and significance is represented by asterisks (*P⩽0.05 and **P⩽0.01). Black asterisks denote significance between the vaccinated groups and DMEM controls, and grey asterisks represent differences between the vaccinated groups and vector controls.

Figure 4

Decreased pathology in the spleen and lungs corresponds to increased survival. Pathology scores ranging from 0 to 4 were assigned to the lung and spleen sections from each group of four animals collected at 5 days after challenge. Results of clinical scoring of brain tissue are not shown because no changes were observed. Groups of animals that were protected by vaccination in the survival experiment are designated by (+), partially protected by (±) and groups not protected by (−). Bars represent the mean of each group and error bars indicate s.e.m. Kruskal–Wallis analysis with a Dunn’s post test was performed, and significance is represented by asterisks (*P⩽0.05, **P⩽0.01 and ***P⩽0.001). Black asterisks denote significance between vaccinated groups and DMEM controls, and grey asterisks represent differences between the vaccinated groups and vector controls. The scoring criteria were as follows: 0=no lesions; 1=focal to few multifocal mild lesions; 2=multiple multifocal mild-to-moderate lesions; 3=multifocal areas of moderate-to-severe lesions; and 4=extensive areas of lesions and necrosis.

Figure 5

Protective vaccination is associated with reduced Nipah virus pathogenesis. Lung sections from four hamsters per group were collected 5 days after challenge and stained with H&E for histology. (a–f) Taken from representative, unprotected DMEM control animals and show moderate-to-marked interstitial pneumonia with necrosis and inflammation (arrows), and alveolar oedema and fibrin (asterisk). (g–l) Derived from rVSV-EBOV-GP-NiV-G animals. (g) An example of normal tissue from a protected animal. (h, i) Minimal interstitial pneumonia with rare foci of alveolar interstitial inflammation (arrow). (j) Mild interstitial pneumonia with larger more frequent areas of inflammation (arrows). (k, l) Animals with moderate-to-marked interstitial pneumonia with coalescing inflammation in k, and necrosis, inflammation and alveolar oedema, and fibrin (asterisk) in l.