Respiratory syncytial virus (RSV) is a seasonal pathogen that is spread via droplets expelled when an infected person coughs or sneezes. The droplets either directly enter a new infectee through their eyes, nose or mouth, or reach those entry points after landing on a surface touched by the infectee.
SARS-CoV-2 spreads via similar mechanisms. As such, it is possible that increased use of masks, hand washing, and social distancing adopted to combat COVID-19 could result in mild RSV seasons in the northern hemisphere in the coming winters.
Bavarian Nordic is alert to that possibility. The Danish company is due to start a phase 3 clinical trial of its RSV vaccine candidate next year but could defer its plan if the virus is unlikely to be circulating at a high enough level to properly evaluate the efficacy of the prophylactic.
“It is quite clear that if we assess that the prevalence of RSV is too low in the market next year then we will not risk a significant investment in a study like this and then we will change our plans accordingly,” said Henrik Juuel, chief financial officer at Bavarian Nordic, on a second quarter results conference call with investors.
The effect of COVID-19 on the prevalence of RSV is one concern. The other key issue is the overlap between the populations of volunteers targeted by the RSV clinical trial and the numerous studies of COVID-19 vaccines. Competition for volunteers could slow enrollment in the RSV study.
For now, Bavarian Nordic is still planning to start the phase 3 clinical trial next year. However, it will assess the feasibility of doing so before fully committing to a study that is expected to cost up to $110 million.
Bavarian Nordic plans to start vaccinating subjects in around 12 months’ time, enabling it to assess the efficacy of its candidate when the RSV season starts in September 2021. The plan is to spend $40 million on enrolling, vaccinating and monitoring 6,000 subjects during the 2021-2022 RSV season.
If the vaccine works well, Bavarian Nordic could stop the trial after a futility analysis scheduled for the summer of 2022. Alternatively, Bavarian Nordic may enroll a further 6,000 to 8,000 subjects, at a cost of up to $70 million, to evaluate its vaccine in a second RSV season.
Bavarian Nordic could advance the RSV vaccine in parallel to a COVID-19 candidate. Having licensed a capsid virus like particle-based SARS-CoV-2 subunit vaccine from AdaptVac, Bavarian Nordic is now seeking funding to support a clinical development program that could bring the candidate to market in the second half of 2021.