USA – Pfizer announced that its respiratory syncytial virus (RSV) vaccine candidate RSVpreF has been designated as a breakthrough therapy by the FDA to prevent RSV-associated lower respiratory tract illness in infants from birth to six months of age through active immunization of pregnant women.

The announcement comes just days after GlaxoSmithKline halted research on its maternal RSV vaccine candidate in pregnant women due to a possible safety signal.

Kathrin Jansen, head of vaccine R&D at Pfizer, noted that “if approved by the FDA, this maternal immunization has the potential to be the first vaccine candidate to help protect infants in their vulnerable first months of life from disease caused by this highly-contagious virus.”

RSV is a leading cause of pneumonia in toddlers and the elderly, but vaccine development has been hampered for decades due to setbacks.

However, many pharmaceutical companies are working to bring a candidate to market within the next few years.

The breakthrough status was granted based on the findings of a Phase IIb study that compared RSVpreF to placebo in 1154 healthy pregnant women aged 18 to 49 who were vaccinated between 28 and 36 weeks of gestation.

The trial will also look at the safety and properties of transplacentally transferred antibodies in their offspring.

Pfizer says it will publish the trial results at a later date. Meanwhile, a Phase III study of its vaccine candidate, PF-06482077, is underway, with data readout expected in the coming months.

GlaxoSmithKline announced earlier this week that it had ceased enrollment and administration of its own experimental RSV vaccine in three trials involving pregnant women, including the Phase III GRACE study.

The decision came shortly after the company paused enrollment in the trials, citing “an observation from a routine safety assessment,” but providing no further details.

GlaxoSmithKline has stated that the decision has no bearing on the ongoing Phase III AReSVi 006 trial of its RSV vaccine in older adults, with results expected in the first half.

Meanwhile, Sanofi and AstraZeneca are co-developing nirsevimab in infants, and Moderna has recently begun testing its mRNA-based candidate mRNA-1345 in a Phase III trial in older adults.

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