Data on a prefusion respiratory syncytial virus (RSV) fusion glycoprotein (F) subunit vaccine antigen strongly support this vaccine’s development as a method of preventing RSV disease in infants by immunizing pregnant women, according to research presented at IDWeek 2019 held October 2 to 6, in Washington, DC. Direct immunization of older adults can also prevent RSV disease in this population.

The RSV F molecule, engineered by Pfizer, fuses viral and host cell membranes during virus entry while rearranging itself from meta-stable prefusion to stable postfusion conformation. Pfizer recently conducted a first-in-human, phase 1/2, placebo-controlled randomized observer-blind dose-finding study of a newly engineered prefusion RSV F subunit vaccine antigen with well-characterized and stable conformational homogeneity. Healthy men and women between the ages of 18 and 85 years (N=1182) were enrolled in the study, which compared 3 vaccine candidate dosages, with and without aluminum hydroxide, and it also compared the RSV vaccine candidate immunization alone or concomitant with the influenza vaccine.

This study is ongoing, with data currently available for the 18 to49 year old subgroup. The current data show an excellent safety and tolerability profile, with the candidate vaccine eliciting RSV 50% neutralization titer geometric mean fold rises of 10.6 to 17.2 for subgroup A and 10.4 to 19.8 for subgroup B, as measured 1 month postimmunization, with evidence of a dose response.

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Study investigators concluded, “The 10 [to] 20 fold increases in neutralizing antibody titers elicited by this vaccine with a stable prefusion F antigen represent a step change relative to the historical performance of vaccine candidates, such as Wyeth’s PFP, with F antigens that were not stabilized in the prefusion conformation (Simoes et al, Vaccine 20:954-60, 2002). The data strongly support development of this vaccine candidate to prevent RSV disease in infants, by immunizing pregnant women, and to prevent RSV disease in older adults, by direct immunization.”

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Disclosure: This study was supported by Pfizer Pharma GmbH, Berlin, Germany. Please see the original reference for a full list of authors’ disclosures.


Schmoele-Thoma B, Falsey AR, Walsh EE, et al. Phase 1/2, first-in-human study of the safety, tolerability, and immunogenicity of a RSV prefusion F-based subunit vaccine candidate. Poster presented at: IDWeek 2019; October 2-6, 2019; Washington, DC. Poster 2755.