Novavax, Rockville, Md, successfully completed a preclinical safety and efficacy study of its respiratory syncytial virus (RSV) vaccine candidate in cotton rats. According to the company, the results of this study are needed to support an Investigational New Drug (IND) application to advance the novel recombinant F protein particle-based RSV (RSV-F) vaccine candidate into clinical development.

Novavax tested its RSV-F vaccine candidate in cotton rats because the animal model is well accepted for RSV infection and disease. The animals received two injections on days one and 21 with 1, 6, or 30 micrograms of RSV-F vaccine with or without an alum adjuvant. All dose groups produced antibodies that neutralize RSV, and with adjuvant, only a single injection of RSV-F was needed to induce high levels of neutralizing antibodies. The immunized cotton rats were challenged with live RSV to test if they were protected from infection. No RSV was detected in the lungs of animals immunized with any dose of the Novavax RSV-F vaccine, with or without adjuvant, while high levels of virus were measured in unimmunized control animals but.

The lungs of RSV challenged cotton rats were examined and there was no sign that immunization with the Novavax RSV-F vaccine candidate resulted in enhanced disease. However, RSV-induced pathology in the lungs was observed in animals immunized with a formalin-inactivated RSV control.

The announcement from Novavax explains that RSV vaccines require a heightened evaluation of safety because of a failed study in children in the mid-1960s with a formalin-inactivated RSV vaccine candidate that caused enhancement of the disease.

"We are excited to report steady progress towards the development of a vaccine against RSV, an important virus that is the leading cause of viral death in infants," said Rahul Singhvi, ScD, president and chief executive officer of Novavax. "A safe and effective vaccine against RSV is especially needed in very young children since RSV infection does not provoke lasting immunity. An effective vaccine would also be important in adults, especially the elderly, where RSV illness is common. There is currently no approved vaccine for the prevention of RSV and the market potential for such a vaccine could exceed $1 billion annually."