Respiratory Syncytial Virus (RSV) is a contagious virus (germ) that circulates particularly during the winter months and throughout the year in some parts of the world. It is transmitted through droplets containing the virus when someone infected sneezes or coughs. In most infants, the RSV infection will be a mild illness similar to a cold, with symptoms such as fever, runny nose, sore throat, ear infection, cough, and croup (barky cough with hoarseness). In some cases, RSV can cause serious lung illnesses such as pneumonia and bronchiolitis (an infection of small airways in the lung called bronchioles), which may lead to hospitalization. At this time, there is no approved vaccine to prevent RSV illness.

The investigational RSVt vaccine in this study contains a live, weakened form of the virus (that is, attenuated) and is given as a nasal spray. It is made to help a person’s body respond in a way that will protect them from getting sick from the virus. The vaccine has been tested in humans before, and other live attenuated RSV vaccines very similar to this one has also been tested in both adults and children. A total of 6300 children are planned to be enrolled worldwide. Eligible participants will be randomized in a 1:1 ratio to receive 2 intranasal administrations 56 days apart of either the RSVt vaccine or placebo at day 1 and day 57 of the study. Additional illness visits may occur during the study for those who develops RSV like symptoms. Each participant will be followed for 24 months in the study. Kenya will enroll approximately 15000 up to 1000 children.

The trial will target recruitment of people from different races and ethnic groups that at a minimum will be representative of the countries in which the trial will be conducted.

Respiratory syncytial virus (RSV) is the most important cause of severe acute lower respiratory illness in infants and children and the most common cause of severe pneumonia requiring hospital admission in children worldwide. According to global estimates, RSV caused approximately 33 million cases of lower respiratory illness and approximately 118,000 deaths in children < 5 years of age in 2015.Infants and young children are at increased risk for RSV infections because of their maturing immune system and lack of prior exposure to RSV.

A genetically stable live-attenuated RSV ΔNS2/Δ1313/I1314L vaccine has been shown to be safe and immunogenic in RSV-seronegative children in Phase I studies with further research ongoing in RSV-seropositive children. Sanofi is conducting clinical studies with a similar RSV ΔNS2/Δ1313/I1314L vaccine, referred to as RSVt vaccine, as part of the Phase III development of the RSVt vaccine (the VAD0004 study).The VAD0004 study, is a Phase III, randomized, observer-blind, placebo-controlled, multi-center, multinational study to evaluate the efficacy, immunogenicity, and safety of a Respiratory Syncytial Virus vaccine in infants and toddlers. The study is designed to evaluate the efficacy, immunogenicity, and safety of RSVt vaccine administered by intranasal route and compared to placebo.

Overall, a global sample size of approximately 6300 participants 6 months to < 22 months of age will be enrolled in the study. Kenya site will enroll approximately 1500 participants. Eligible participants will be randomized in a 1:1 ratio to receive 2 intranasal administrations of either the RSVt vaccine or placebo.Study duration will be 24months for each participant. The safety evaluation will start after the first vaccination and up to the end of the study. The trial will target recruitment of people from different races and ethnic groups that at a minimum will be representative of the countries in which the trial will be conducted.