A new type of vectored vaccine for respiratory syncytial virus (RSV), a virus that causes respiratory disease in humans, has been shown by scientists at Pirbright to provide immunity against a closely related virus in calves, giving strong evidence that a similar type of vaccine could work in humans.
Human respiratory syncytial virus (HRSV) is a leading cause of bronchiolitis and severe respiratory disease in infants, young children, immune-compromised individuals and the elderly. Worldwide it causes 200,000 deaths per year in children under the age of five and there is currently no vaccine. Development of a suitable vaccine candidate has been hindered by the young age of the main target population making clinical trials difficult and increased caution following the aftermath of a failed clinical trial of a formalin-inactivated RSV vaccine (FI-RSV) conducted in the 1960’s. This inactivated vaccine candidate led to enhanced disease and hospitalisation of 80% of the vaccine recipients, including two fatalities.
The new research demonstrates that calves vaccinated with an adenovirus-vector expressing HSRV proteins protected them from bovine (B)RSV infection.
Leading the study was The Pirbright Institute’s Head of Vaccinology, Dr Geraldine Taylor. She said, “Our studies have provided solid pre-clinical data on the safety and efficacy of a viral-vectored HRSV vaccine in calves with bovine respiratory syncytial virus infection (BRSV).”
Previous studies with this adenovirus-vectored vaccine candidate, which was developed by ReiThera in collaboration with Pirbright, have shown that the HRSV vaccine initiates protective immune response rats and mice. However, these animals are not the natural host of the virus and therefore do not provide a clear picture as to what extent the vaccine would provide protection in humans. By studying the effects of the vaccine in calves, which are natural hosts of the closely related BRSV, scientists have been able to get a more promising indication that the vaccine might also work in humans.
“The failure of small animals to predict HRSV vaccine efficacy and safety in humans highlighted the need for studies in animal model that more closely resembles HRSV infection and disease in infants,” explains Geraldine. “The human strain of the virus is closely related to the bovine strain, both viruses cause respiratory disease in their respective hosts and the epidemiology and pathogenesis of infection are also similar.”
The results of this study combined with the knowledge that human and chimpanzee adenovirus-vectored vaccines for other viral diseases have been shown to be safe in humans, has led the Oxford Vaccine Group at the University of Oxford to begin a clinical trial in humans.