Novavax acknowledged that its respiratory syncytial virus (RSV) F-protein recombinant nanoparticle vaccine candidate failed a Phase III trial, sending the company’s shares crashing by more than three-quarters in after-hours trading.

RSV F Vaccine missed its primary and secondary efficacy endpoints in the Phase III Resolve trial, in which the vaccine was given to 11,856 adults aged 60 and older.

The trial’s primary objective was to show the RSV F Vaccine’s efficacy in preventing moderate-severe RSV-associated lower respiratory tract disease (RSV msLRTD), defined by the presence of multiple lower respiratory tract symptoms. The secondary objective called for demonstrating efficacy in reducing the incidence of all symptomatic respiratory disease due to RSV (RSV ARD [acute respiratory disease]).

“We are both surprised and disappointed by the outcome of the Resolve trial,” Gregory Glenn M.D., Novavax president, R&D, said in a statement. “We are continuing to investigate potential root causes that could have impacted the outcome of this trial. We continue to believe that there is a path forward for our RSV vaccine and that there is an important unmet need for an RSV vaccine in older adults.”

Dr. Glenn said Novavax’s initial analyses and review of the trial indicated no issues with trial execution, data collection, data integrity, or drug product quality, adding: “We expect to have preliminary immunogenicity data in the coming weeks to further our understanding of the trial results.”

Resolve was a randomized, observer-blinded, placebo-controlled trial conducted at 60 U.S. sites.

Novavax’s announcement of the Resolve trial failure included results from a Phase II rollover study of the vaccine in 1329 older adults who were patients in a prior successful Phase II trial, whose primary objectives assessed safety and serum anti-F immunoglobulin G (IgG) antibody concentrations in response to immunization with the RSV F Vaccine. The Phase II study also evaluated the efficacy of a second annual dose of the RSV F Vaccine in preventing RSV ARD and RSV msLRTD.

“We observed similar low attack rates and absence of efficacy of a single immunization in this trial as was observed in [the] Phase III Resolve trial, although we did observe that a second season immunization could provide efficacy,” Dr. Glenn said.

Stanley C. Erck, Novavax president and CEO, stated that the company intends to provide a more in-depth update on the Phase III trial and Phase II rollover study on October 11 at its investor and analyst meeting.

Investors, however, wasted little time responding to the trial setbacks with a stock selloff that sent shares of Novavax plunging 86% from yesterday’s closing price of $8.34 per share, to $1.15 as of 8:57 a.m.

Previous articleNew Approach Tackles Multiple Sclerosis by Targeting Lymph Nodes
Next articleMysterious New Mosquito-Borne Disease Found in Caribbean