Moderna’s RSV Vaccine Efficacy Sparks Investor Concern

Update 1:23 PM EST: Adds comments from Moderna (NASDAQ:MRNA)

Moderna’s (MRNA) shares took a hit in the stock market today amid concerns over the long-term effectiveness of the company’s experimental vaccine designed to combat respiratory syncytial virus (RSV), compared to similar vaccines from competitors such as Pfizer (PFE) and GSK (GSK).

The Cambridge, Massachusetts-based biotech saw a startling 7% drop in value during afternoon trading, marking its most significant intraday loss since September.

Analysts from TD Cowen and UBS raised red flags following data from a Phase 3 trial, which suggested that Moderna’s (MRNA) mRNA-1345 vaccine demonstrated a decline in efficacy against two symptoms of RSV to approximately 63% from the initial 84% over an eight-month period.

TD Cowen analyst Tyler Van Buren highlighted that Arexvy and Abrysvo, the FDA-approved RSV vaccines from GSK (GSK) and Pfizer (PFE), exhibited a decline in efficacy from 83% to 77% and 89% to 79% over 14 and 17 months, respectively, against three symptoms.

“We note these are slightly different endpoints, but are concerned it could negatively affect 1345’s profile if confirmed with additional data,” Van Buren wrote.

In defense, Moderna (MRNA) argued that cross-comparisons across different time frames are complex due to the varying severity of RSV and its modes of transmission, which can fluctuate from season to season.

Additionally, drawing conclusions about the efficacy of the vaccine compared to other RSV shots will prove daunting without head-to-head clinical studies, the company further added in a statement. “These trials differed in study populations, geographic locations, infection surveillance methods, and case definitions used for RSV,” Moderna (MRNA) pointed out.

Despite the setback, the company has proceeded with regulatory submissions for the vaccine globally, seeking approvals in the first half of 2024.