GSK today announced positive pivotal phase III trial results for its respiratory syncytial virus (RSV) vaccine candidate for adults aged 60 years and above to be presented at IDWeek 2022. The vaccine candidate was highly efficacious, demonstrating overall vaccine efficacy of 82.6% (96.95% CI, 57.9–94.1, 7 of 12,466 vs. 40 of 12,494) against RSV lower respiratory tract disease (RSV-LRTD), meeting the trial’s primary endpoint.

Ahead of the company’s IDWeek 2022 presentation, GSK released efficacy results from a phase III trial of RSV OA in older adults. GSK reported 82.6% efficacy against Lower Respiratory Tract Disease (LRTD) overall and 94.1% against “severe” LRTD with ≥2 signs. Although RSV OA and Pfizer’s RSVpreF have not been tested in a head-to-head trial and used different endpoints in their respective studies, investors and buyers are likely to still compare GSK and Pfizer’s recent results. 

Of note, GSK defined severe LRTD as LRTD with ≥2 respiratory signs or confirmed as severe by external committee, whereas Pfizer defined Lower Respiratory Tract Infection (LRTI) for its overall protection as having ≥2 symptoms. The strong efficacy results from GSK may push the price it can command as well as future market share up, but Pfizer may still have an edge in tolerability. Neither company has released detailed phase III tolerability data but adjuvanted vaccines such as RSV OA tend to be more reactogenic.

The race to approval

Both GSK and Pfizer have announced regulatory submissions in the next few months, Pfizer in Autumn 2022 and GSK in H2 2022. Both companies are ahead of the other three phase III rivals: Ad26.RSV.preF from Janssen, mRNA-1345 from Moderna, and MVA-BN-RSV from Bavarian Nordic. Previous announcements from Pfizer had anticipated a 2025 launch for Pfizer’s RSVpreF, but 2023 is much more likely for both Pfizer and GSK at this point. In the US, Pfizer enjoys a slight edge in terms of timing as RSVpreF has Breakthrough Therapy designation, compared to only Fast Track status for GSK’s RSV OA. However, as both products could be marketed ahead of the 2023 RSV season, a first-to-market advantage of a month or two may be limited or non-existent. Market share may instead be dictated more by efficacy, tolerability, and marketing budgets.

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