Federal officials are examining a first-of-its-kind vaccine that would be given to pregnant women to protect the developing baby against the respiratory virus called RSV.

An advisory panel for the Food and Drug Administration met to discuss approval for the shot. Pfizer’s experimental RSV vaccine would be given in late pregnancy, so mothers can pass antibodies on to their babies to protect against the virus.

Pfizer says its research of nearly 7,400 vaccinated mothers finds the shot is 82% effective at preventing severe RSV in infants in the first three months of life.
That number is 69% at six months.

Reviewers with the FDA say the vaccine appears to be safe, but there are some questions about a slight difference in premature birth in the two study groups.

“A difference of 1% was noted in premature births similar to the difference seen in preterm delivery; though not statistically significant, these findings may be of consideration for further safety evaluation for post-marketing studies,” said FDA Participant Yugenia Hong-Nguyen.

RSV stands for respiratory syncytial virus and can be dangerous, even deadly, for some infants and young children.

The CDC estimates about 58,000 to 80,000 children under five are hospitalized due to RSV. Premature babies and infants under six months old are at the highest risk for severe RSV illness.

The U.S. experienced an unprecedented early and severe surge in RSV cases last fall, putting a significant strain on hospitals. Pfizer predicts up to 16,000 infant hospitalizations could be prevented each year if pregnant women are vaccinated for RSV.