In a feature for The BMJ in November 2023 Hristio Boytchev reports on concern raised by “some experts” that Pfizer should have informed pregnant participants in a respiratory syncytial virus (RSV) vaccine trial that a similar vaccine trial was paused over a risk of preterm birth. While this has caused discontent for one group, other suggest that notification would have been “premature and caused unnecessary anxiety”. So, what should have been done? 

The RSV race 

Both GSK and Pfizer have been working on recombinant RSV F protein vaccines for administration during pregnancy with the goal of protecting infants against RSV. WHO describes human RSV as a “globally prevalent” cause of lower respiratory tract infection in “all age groups”, yet in younger children the first infection can cause severed bronchiolitis that “can sometimes be fatal”.  

GSK shared in February 2022 that “following a recommendation” from the Independent Data Monitoring Committee it had “voluntarily paused enrolment” in the GRACE trial and two other trials investigating the potential RSV maternal vaccine candidate. 10 days after the first update, GSK confirmed that enrolment and vaccination had stopped. 

“Further analysis to better understand safety data from these trials is ongoing, and the relevant regulatory authorities have been informed.” 

Subsequent reports to the FDA Vaccines and Related Biological Products Advisory Committee in 2023 state that the safety signals were an “imbalance” in the proportions of preterm births and neonatal deaths between the vaccine and placebo groups. At the time, GSK did not have a “mechanistic explanation” for this. Indeed, Boytchev reflects that “experts think it might be unrelated to the vaccine”; the imbalance was “primarily observed” in LMICs and inconsistently after a peak. However, GSK continued investigations and stopped development.  

What should Pfizer have done? 

Following this, “opinion was split” among ethicists and researchers, who questioned whether Pfizer should have informed trial participants about the potential risk. For example, Western University’s Dr Charles Weijer told The BMJ that this would have been the right choice, calling “any failure” to update safety information data “ethically problematic”. Professor Dr Klaus Überla, University Hospital Erlangen, advised The BMJ that following the publication of results from the GSK trial, other vaccine studies should be “updated” to include the potential risk.  

On the other hand, Professor Beate Kampmann, director of the Centre for Global Health at Charité University Hospital Berlin and a lead author of Pfizer’s Phase III trial publication, suggested that the GSK results were irrelevant to her participants, most of whom “were already in follow-up”. Indeed, she considered the context of the safety concerns different to her own trial. 

“This was a very location specific and also transient finding, which remains poorly understood.” 

We encourage readers to check out Boytchev’s investigatory piece here for the full story, and don’t hesitate to join the discussion below. To further the discussion, why not join us in Santa Clara to hear more from representatives of Pfizer? If you can’t make it, do subscribe to our weekly newsletter here.