Experts Diverge on the Necessity of Informing Pregnant Women About Similar Vaccine’s Risks in Pfizer’s RSV Trial.
A contentious discussion has emerged regarding Pfizer’s responsibility to inform pregnant participants in its respiratory syncytial virus (RSV) vaccine trial about the halted trial of a similar vaccine due to concerns over preterm birth. This issue, highlighted in a report by The BMJ, has ignited a debate among experts in the field. Both Pfizer and GSK have been developing recombinant RSV F protein vaccines, aimed at immunizing pregnant women to protect their babies against RSV, a significant cause of infant mortality worldwide.
In February 2022, GSK suspended its phase 3 vaccine trial following a safety signal indicating a potential rise in preterm births and neonatal deaths. The observed rates of preterm birth in the vaccine group were higher compared to the placebo group, though no definitive cause for this increase was identified. GSK, in its communication with The BMJ, noted that the observed imbalance was primarily in low and middle-income countries and was not consistently present after late 2021. Despite ongoing investigations, GSK ceased the development of its vaccine.
Meanwhile, Pfizer’s phase 3 trial also monitored preterm births as a special interest adverse event. Their recent data showed a slight, but not statistically significant, imbalance in preterm births between the vaccine and placebo groups. The debate intensifies over whether Pfizer should have updated its trial participants about the potential risk identified in GSK’s trial, especially in light of the lack of conclusive evidence or explanation for the increased risk of preterm birth.
Charles Weijer, a bioethics professor, argued that informing participants in Pfizer’s trial about GSK’s findings would have been ethically appropriate, allowing women to make informed decisions about participating in the trial or seeking additional medical advice. Conversely, Stephen Evans, a professor of pharmacoepidemiology, emphasized the role of the independent Data and Safety Monitoring Board (DSMB) in assessing such risks and making decisions based on a comprehensive benefit-harm balance, rather than solely on statistical significance.
The DSMB for Pfizer’s trial did not publicly address whether it had considered the GSK results. Additionally, Pfizer faced criticism for some language in its trial consent forms, which were described as potentially misleading regarding the vaccine’s safety for unborn babies. These concerns about informed consent were amplified by Pfizer’s lack of response to queries about the issue.
After GSK halted its trial, there was a call for further analysis of Pfizer’s phase 3 trial data, particularly in light of the slight increase in preterm births observed. The US Food and Drug Administration’s advisory committee, after evaluating the data, found the Pfizer vaccine to be safe, though some members expressed concerns about the adequacy of the data in supporting safety, particularly regarding preterm births.
Different regulatory bodies have taken varied approaches to Pfizer’s vaccine, named Abrysvo. The FDA approved it with specific conditions, including restricting its administration to pregnant women between 32-36 weeks of gestation, due to insufficient data to establish or exclude a causal relationship with preterm birth. Other agencies, like the European Medicines Agency, did not find it necessary to include a warning about preterm birth risk or restrict the vaccine’s use to later stages of pregnancy.
The debate over whether trial participants should have been informed about the potential risk of preterm birth following the public disclosure of GSK’s trial results remains unresolved. Some experts, including Klaus Überla and Rose Bernabe, advocate for the renewal of informed consent under such circumstances, citing international guidelines. However, others, including Beate Kampmann and Joop van Gerven, argue that amending consent forms was not warranted due to the uncertain nature of the risk and its potential to cause undue anxiety among participants.
Pfizer’s consent forms have also been a point of contention. They did not explicitly disclose that preterm birth was being studied as an adverse event of special interest, and contained contradictory statements regarding the risks to the unborn baby. This has led to criticism from experts like Bernabe, who called the statement in the consent forms “irresponsible” and potentially misleading.
In response to these concerns, national research ethics bodies like the Dutch CCMO have acknowledged the potential for confusion in the consent forms and recommended Pfizer to adapt the wording. However, the debate over the adequacy of informed consent and the ethical implications of non-disclosure in clinical trials remains a critical issue in the field of medical research ethics.
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