Journal of virologyJul 28, 2026

Testing a vaccine targeting multiple proteins of EEHV1A in Asian elephants

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Updated Aug 3, 2026

Abstract

The EEHV1A vaccine elicited robust immune responses in Asian elephants, with some seronegative individuals showing antibody levels up to 50% of those in experienced elephants.

EEHV is associated with fatal hemorrhagic disease in juvenile Asian elephants, particularly those aged 1-8 years.
Current supportive treatments for EEHV are not consistently effective, highlighting the need for new preventative strategies.
The developed mRNA vaccine targets four herpesvirus entry proteins and generated strong immune responses in mice without adverse effects.
In a trial with nine Asian elephants, seropositive individuals showed increased antibody levels to all four vaccine antigens.
Seronegative elephants exhibited stronger responses to two of the antigens, while maintaining variable responses to the others.
Sustained antibody level increases were observed in both seropositive and seronegative groups for up to 192 days post-vaccination.

Simplified

Elephant endotheliotropic herpesvirus (EEHV) is endemic in Asian elephants and can cause fatal hemorrhagic disease (HD) in juveniles, with calves aged 1-8 years being most vulnerable, particularly following the decline of maternal antibodies. Current supportive treatments, which commonly include fluids, plasma infusions, and human anti-herpesvirus drugs, are not consistently effective, highlighting the urgent need for preventative strategies. To address this challenge, we generated an EEHV1A multi-antigen mRNA vaccine targeting four conserved herpesvirus entry proteins (gB, gH, gL, and gO), which elicited robust humoral and cellular immune responses in mice without adverse effects. Based on these preclinical findings, a vaccine trial was conducted in nine Asian elephants, comprising three seropositive and six seronegative individuals. Animals received up to four 400 μg doses intramuscularly 3 weeks apart, with serum samples collected at baseline (day 0), post-booster (day 42), and monthly through day 192. Seropositive elephants demonstrated anamnestic responses with increased antibody levels to all four vaccine antigens individually. Seronegative elephants responded more robustly to gH and gL versus variable responses to gB and gO. Enzyme-linked immunosorbent assays (ELISAs) detecting the gH/gL/gO trimer indicate sustained antibody level increases in both sero-positive and sero-negative groups, persisting up to 192 days post-vaccination in seropositive elephants. Notably, post-vaccine titers against the trimer in some seronegative elephants reached up to 50% of baseline levels observed in EEHV-experienced subadult and adult elephants. These findings represent a critical advancement toward an effective EEHV1A vaccine to reduce HD mortality and support Asian elephant conservation efforts.

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Testing a vaccine targeting multiple proteins of EEHV1A in Asian elephants

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