Candidate Vaccine for RSV Appears Safe, Effective Among Nonpregnant Women

A single dose of an investigational vaccine for respiratory syncytial virus (RSV) appears to be safe and effective among healthy women of childbearing age who are not pregnant, according to results of a new phase 2 study. 

To evaluate the immunogenicity and tolerability of the RSV candidate vaccine, the researchers equally randomly assigned 400 healthy women aged 18 to 45 years who were not pregnant to receive a single intramuscular dose of vaccine containing 30 µg, 60 µg, or 120 µg of RSV fusion protein engineered to preferentially maintain a prefusion conformation (RSV-PreF vaccine) or placebo.

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From baseline to 30 days after the women received vaccination, RSV-A neutralizing antibody geometric mean titers (GMTs) increased 3.75-fold among the 30 µg group, 4.42-fold among the 60 µg group, and 4.36-fold among the 120 µg RSV-PreF group.

In that same timeframe, RSV-B neutralizing antibody GMTs increased 2.36-fold among the 30 µg group, 2.54-fold among the 60 µg group, and 2.76-fold among the 120 µg group. 

Palivizumab competing antibody (PCA) concentrations also increased from baseline to day 30, by 11.69-fold among the 30 µg group, 14.38-fold among the 60 µg group, and 14.24-fold among the 120 µg group.

At day 30, antibody titers and PCA concentrations among the 120 µg group RSV-PreF vaccine were significantly higher than among the 30 µg group RSV-PreF vaccine.

The reactogenicity profiles of all of the RSV-PreF vaccine formulations, as well as the placebo, were similar, with no serious adverse events related to the RSV-PreF vaccine.

“In summary, this study showed that the 3 formulations of the investigational RSV-PreF vaccine containing up to 120 µg of RSV-PreF protein were well-tolerated and boosted preexisting immune responses,” the researchers concluded. “The rise in antibody titers with increasing dose levels was less than linear and suggests that the benefit of increasing dose levels of this antigen beyond 120 µg may be limited.”

—Colleen Murphy

Reference:

Schwarz TF, McPhee RA, Launay O, et al. Immunogenicity and safety of 3 formulations of a respiratory syncytial virus candidate vaccine in nonpregnant women: a phase 2, randomized trial. J Infect Dis. 2019;220(11):1816-1825. https://doi.org/10.1093/infdis/jiz395.