Advantage Pfizer: GSK stops phase 3 trials of maternal RSV vaccine after seeing safety signal

Hopes of a quick fix for GlaxoSmithKline’s respiratory syncytial virus (RSV) vaccine woes are fading fast. Having voluntarily paused three maternal RSV vaccine clinical trials 10 days ago, GSK has now stopped enrollment and vaccination in the studies as it works to better understand the safety data.

Details of the situation, which began when an independent data monitoring committee recommended a pause in response to a safety assessment, remain scarce. The latest update provides no information on the nature of the safety signal, but whatever GSK learned over the past 10 days persuaded it to stop rather than just pause its maternal RSV vaccine studies.

“GlaxoSmithKline today announced that, further to the voluntary pause shared on February 18, the Company has decided to stop enrolment and vaccination in trials evaluating its potential [RSV] maternal vaccine candidate in pregnant women. Further analysis to better understand safety data from these trials is ongoing, and the relevant regulatory authorities have been informed,” GSK wrote in a statement.

A phase 3 clinical trial in older adults is continuing as planned and is still scheduled to deliver data by the midpoint of the year. GSK had aimed to publish maternal data by the end of 2022. The centerpiece of the maternal RSV vaccine development program is the 20,000-subject GRACE trial. GSK has stopped that key trial and two smaller studies, one of which was yet to start recruiting when the safety signal emerged. 

RELATED: GSK slams brakes on maternal RSV vaccine over safety signal

The troubles at GSK give Pfizer a shot at dominating the maternal RSV vaccine market. Pfizer was in a close race against GSK, with data on its maternal RSV vaccine candidate due in the first half of 2022, but it could now enjoy a prolonged period on the market in which it is free from direct competition.

Whatever happens with GSK, Pfizer will likely need to compete against AstraZeneca and Sanofi’s different way of protecting babies from RSV. Rather than vaccinate pregnant women, AstraZeneca and Sanofi plan to administer a long-acting antibody to infants before their first RSV season. Having hit the mark in phase 2/3, the partners are aiming to win approval for nirsevimab in Europe in the second half of 2022.