Obstetrics & gynaecology

After studies suggested a potential rise in preterm deliveries, experts called urgent monitoring of the respiratory vaccine.

After trials of a similar GSK vaccine were halted due to an increase in preterm births and infant deaths, experts have called for additional investigation of the Pfizer vaccine, which is administered during pregnancy to prevent respiratory infections in infants.

Pfizer claims that its vaccine is safe and effective, but experts interviewed for an investigation that was published today in The BMJ say that Pfizer’s trial data should be looked at in light of the signal for preterm births seen in GSK’s trial.

The goal of the maternal RSV vaccine from Pfizer is to prevent severe respiratory syncytial virus (RSV) illness in infants. Despite its prevalence, RSV can be fatal, particularly in young children. RSV was responsible for an estimated 3.6 percent of all deaths in children aged 1 to 6 months worldwide in 2019, with 97% of these deaths occurring in low- and middle-income nations.

“Based on all of these data, I believe there may be a safety signal for preterm births that needs to be investigated,”

Klaus Überla, director of the Virological Institute of the University Hospital Erlangen.

The use of the vaccine has not yet been approved, but the Food and Drug Administration of the United States is expected to make a decision by August. A decision regarding the vaccine will also be made by the European Medicines Agency later this year.

After discovering an increased risk of preterm birth in vaccinated mothers, primarily in low- and middle-income countries, in its phase 3 trials of its maternal RSV vaccine, GSK stopped administering the vaccine in February 2022.

Pfizer announced last month the findings of an interim analysis of its phase 3 trial, stating that the vaccine was safe and effective against medically treated severe RSV in children.

Even though the difference in preterm births in the Pfizer trials was not statistically significant, experts are now calling for additional data analysis and post-approval monitoring of the vaccine in the event that the FDA approves it.

Klaus Überla, director of the Virological Institute at the University Hospital Erlangen and member of the RSV working group of the Standing Committee on Vaccination (STIKO), which develops national recommendations for the use of licensed vaccines in Germany, stated, “My interpretation of all these data is that there may be a safety signal for preterm births that should be followed up on.”

Additionally, in order to identify potential signals, a scientist at the National Institutes of Health (NIH) stated that the Pfizer data should be analyzed using more sensitive measures like average birth weight and subgroup analyses.

In the meantime, Cody Meissner, a professor of pediatrics and medicine at the Dartmouth Geisel School of Medicine and a consultant to the maternal RSV working group of the US Centers for Disease Control and Prevention (CDC), anticipates that potential negative effects, such as preterm births, will be “closely monitored” in the FDA and CDC assessment programs. We require a vaccine that is safe,” he added.

Pfizer didn’t answer when gotten some information about a potential expansion in preterm births related with its immunization, yet let The BMJ know that “no irregularity of neonatal passings was noticed” in its stage 3 preliminary.

In a related editorial, researchers discuss the main approaches being pursued to protect against RSV and the difficulties encountered in developing a vaccine.

They argue that, despite the substantial global burden of RSV-related illness, it is especially crucial that infants in low- and middle-income countries, where the greatest number of illnesses and deaths occur, receive new vaccines and other preventative measures.

“To identify the best prevention strategies for low and middle income countries, where affordability is paramount and timing of administration is complicated by the lack of predictable seasonal RSV epidemics,” they add, adding that additional research is required immediately.

More information: Maternal RSV vaccine: Further analysis is urged on preterm births, The BMJ (2023). DOI: 10.1136/bmj.p1021

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