The equine Hendra virus vaccine remains a highly effective preventative measure against infection in horses and humans: ‘The imperative to develop a human vaccine for the Hendra virus in Australia’.

This research counteracts an article proposing that the Hendra virus (HeV) is rapidly mutating, rendering the current equine HeV vaccine ineffective and changing human clinical syndromes. The researchers refute these claims as lacking scientific evidence, arguing that the HeV genome demonstrates minimal variability as observed in both flying-foxes and horses. Moreover, they contend that there have been no instances of HeV infections in vaccinated horses, endorsing the efficacy and safety of the equine HeV vaccine. They also denounce the idea of HeV altering clinically in humans and searching for new host species.

The Hendra Virus and its Mutation Rate

• Contrary to the claims of Zahoor and Mudie that the Hendra virus is rapidly mutating, the authors argue that there is no scientific basis for this assertion. They point out that the Hendra virus has shown minimal variability—less than 1%—at both the nucleotide and amino acid levels.
• They dispute the claim of mutation by citing primary research showing that the Hendra virus is highly stable, with instances of the same variant being detected at different locations simultaneously and consistently over twelve years.

Efficacy of the Equine Hendra Virus Vaccine

• The authors challenge the allegation that the equine Hendra virus vaccine is losing its effectiveness. They maintain there is no evidence to indicate this and suggest that sustained occurrences of equine Hendra virus are due to horse owners’ failure to inoculate their animals, rather than reduced vaccine efficacy.
• The evidence to support the effectiveness and safety of the vaccine is clear – no cases of Hendra virus have been observed in vaccinated horses, and both government and animal health authorities strongly recommend the use of the vaccine as an effective risk-reduction measure.

Change in Clinical Patterns in Human HeV Infection

• Referring to claims that human HeV infection is evolving, the authors argue that there is no outstanding evidence to support this. The limited number of recognized human cases share clinical features, but the sample size is too small to establish changes over time.

Infection of New Species

• The authors also refute the assertion that HeV is venturing into new hosts. They clarify that the broad host range of HeV in experimental studies is well-established and that the few observed cases of natural HeV infection in dogs were most likely due to exposure to infected horses or contaminated material from these horses.

Expansion of HeV Infection

• Finally, the authors counter the perception that HeV infections are expanding to locations beyond typical bat migration boundaries. They cite several recent publications indicating that the spatial occurrence of equine HeV cases aligns with the distribution of its known carriers – black and spectacled flying-foxes.