Safety and Immunogenicity of ChAd155-RSV Vaccine in Children 12-23 Months Old

Background

• Respiratory syncytial virus (RSV) is a significant cause of bronchiolitis and pneumonia leading to hospitalization in children.

• An effective vaccine for preventing RSV infection has been elusive for decades.

Study Overview

• The study investigated the safety and immunogenicity of a new candidate RSV vaccine (ChAd155-RSV) in seropositive children aged 12-23 months.

• Phase I/II trial registered as NCT02927873.

• Administered to 12-23-month old RSV-seropositive children, with follow-up for two years after vaccination.

Methods

• Randomized controlled trial with 82 participants receiving either ChAd155-RSV or placebo.

• The dosing regimen escalated from low (0.5×10⁴), medium (1.5×10⁴), to high (5×10⁴) doses based on safety evaluations.

• Endpoints included anti-RSV-A neutralizing antibody titers and safety assessments.

Results

• Participants:

  • 1 participant experienced a mild adverse event (gastroenteritis).

  • No serious adverse events or RSV-related hospitalization occurred.

• Immunogenicity:

  • Dose-dependent increase in RSV-A Nab titers observed after the first dose; titers remained elevated one year after vaccination.

• Adverse Events:

- Most common were mild fevers. Notable adverse events occurred similarly across all study groups.

Conclusion

• ChAd155-RSV was well tolerated, showing positive immune responses without significant adverse effects.

• Further investigation in RSV-seronegative children recommended due to promising results.

Key Terms

• Immunogenicity: Ability of the vaccine to provoke an immune response by inducing antibodies.

• Neutralizing Antibodies (Nabs): Antibodies that can block the infectivity of pathogens, measured here for RSV.

• Vaccine-associated enhanced respiratory disease (VAERD): A phenomenon where vaccination leads to severe disease upon subsequent natural infection, not observed in this study.

Study Significance

• This is one of the first trials to assess a viral vector-based RSV vaccine in young children, marking a step forward in RSV vaccine development.

Respiratory syncytial virus (RSV) is a significant cause of bronchiolitis and pneumonia leading to hospitalization in children, especially among infants and young children. It is one of the most common viral pathogens and typically spreads through respiratory droplets, making outbreaks more likely during the fall and winter months. An effective vaccine for preventing RSV infection has been elusive for decades due to challenges in inducing a robust immune response without causing vaccine-associated enhanced respiratory disease (VAERD).

Study Overview

The current study aims to evaluate the safety and immunogenicity of the ChAd155-RSV vaccine in children aged 12-23 months, which is critical as this age group is particularly vulnerable to severe RSV disease. Through randomized, double-blind methods, participants will receive the vaccine or a placebo, allowing for a comprehensive analysis of immune response and side effects.