Vaccines against human respiratory syncytial virus in clinical trials, where are we now?

Introduction: Human respiratory syncytial virus (RSV) is a major health threat both for the very young and the elderly. With yearly 3.2 million hospital admissions and approximately 118,000 deaths due to RSV in children across the globe, the impact of this infectious disease is very high. Development of a safe RSV vaccine is of utmost importance but has proven to be challenging for several reasons. Researchers are faced with the history of a failed RSV vaccine trial, difficult target populations, a virus that naturally does not induce a long-lasting immune response and ambiguity concerning the optimal correlate of protection. Many different vaccine formats are being tested in preclinical models and about 30 candidate RSV vaccines are being evaluated in clinical trials.Areas covered: In this review we focus on the difficulties concerning the development of an effective RSV vaccine and discuss vaccines that are currently in clinical trials and how they have dealt with these challenges. We review live-attenuated vaccines, vectored vaccines, subunit vaccines and particle-based vaccines.Expert opinion: It is clear that this field is progressing rapidly with several promising RSV vaccine candidates. A safe and effective RSV vaccine might be on the brink of clinical implementation soon.