Objective: To see if a vaccine for RSV is safe and if it causes side effects.

Eligibility: Healthy adults 18-50 years old

Design: Volunteers were screened in a separate screening protocol. Subjects had 13 visits over 1 year.

Some subjects received just the vaccine. Some received vaccines mixed with alum adjuvant. All subjects received their dose by injection in the upper arm. They received up to two doses, one at the beginning of the study and another 12 weeks later.

Subjects were monitored for 1 hour after injection and called to check on their safety 1 day after. Subjects recorded their temperature and side effects for 7 days after each vaccination. Subjects were provided with a thermometer to measure their temperature and a ruler to measure any changes if these occurred on their skin at the injection site.

At all visits, subjects were checked for health changes or problems. 

At some visits, subjects had samples collected from their nose and mouth.

Results

The Lancet published the results of this clinical trial on April 14, 2021.

Findings: Between Feb 21, 2017, and Nov 29, 2018, 244 participants were screened for eligibility and 95 were enrolled to receive DS-Cav1 at the 50 μg (n=30, of which n=15 with AlOH), 150 μg (n=35, of which n=15 with AlOH), or 500 μg (n=30, of which n=15 with AlOH) doses. DS-Cav1 was safe and well tolerated and no serious vaccine-associated adverse events deemed related to the vaccine were identified. DS-Cav1 vaccination elicited robust neutralising activity and binding antibodies by 4 weeks after a single vaccination (p<0·0001 for F-binding and neutralising antibodies). In analyses of exploratory endpoints at week 44, pre-F-binding IgG and neutralising activity were significantly increased compared with baseline in all groups. At week 44, RSV A neutralising activity was 3·1 fold above baseline in the 50 μg group, 3·8 fold in the 150 μg group, and 4·5 fold in the 500 μg group (p<0·0001). RSV B neutralising activity was 2·8 fold above baseline in the 50 μg group, 3·4 fold in the 150 μg group, and 3·7 fold in the 500 μg group (p<0·0001). Pre-F-binding IgG remained significantly 3·2 fold above baseline in the 50 μg group, 3·4 fold in the 150 μg group, and 4·0 fold in the 500 μg group (p<0·0001). Pre-F-binding serum IgA remained 4·1 fold above baseline in the 50 μg group, 4·3 fold in the 150 μg group, and 4·8 fold in the 500 μg group (p<0·0001). Although a higher vaccine dose or second immunisation elicited a transient advantage compared with lower doses or a single immunisation, neither significantly impacted long-term neutralisation. There was no long-term effect of dose, number of vaccinations, or adjuvant on neutralising activity.

Interpretation: In this phase 1 study, DS-Cav1 vaccination was safe and well tolerated. DS-Cav1 vaccination elicited a robust boost in RSV F-specific antibodies and neutralising activity that was sustained above baseline for at least 44 weeks. A single low-dose of pre-F immunisation of antigen-experienced individuals might confer protection that extends throughout an entire RSV season.