Nearly 80% of infants born at Kaiser Permanente Northern California hospitals in late 2023 and early 2024 received a new respiratory syncytial virus (RSV) vaccine from one of 2 new methods, according to a new study published in JAMA Network Open.
“That is pretty high uptake, particularly since these methods are fairly new,” said lead author Karen Jacobson, MD, MPH, a research scientist with the Kaiser Permanente Division of Research. “This widespread use may be because doctors and parents are worried about RSV in young infants. RSV is the No. 1 cause of hospitalization for infants under one year old.”
The study reflects a rapid rollout of a new vaccine for mothers and a separate new RSV preventive treatment for babies, and it examines the use of the RSVpreF vaccine in mothers late in their pregnancies and the use of nirsevimab in infants. The analysis covered 17,251 births between October 2023 and March 2024.
RSVpreF vaccine is given to mothers late in pregnancy (32 to 36 weeks gestation). The maternal vaccine is meant to protect the baby through the mother’s antibodies that cross the placenta.
Nirsevimab, a monoclonal antibody, is given to infants under 8 months old. It is usually given to babies whose mothers did not have the vaccine in pregnancy or received it within 2 weeks of giving birth.
Of the 17,251 infants studied, 77.5% received protection from either RSVpreF vaccine or nirsevimab. Most of those receiving nirsevimab got it in the first 2 weeks of life.
Maternal vaccination differed by the mother’s age and background: 26% of pregnant patients aged 15 to 24 received the vaccine, compared with 35% of those aged 30 to 34. A quarter of Black infants had a mother who received the vaccine, compared with 41% of Asian babies, 33% of white babies, and 30% of Hispanic babies.
However, the study found similar rates of nirsevimab administration across races and ethnicities, with rates slightly higher in Black and Hispanic babies.
This suggests the combination of the two approaches may help avoid disparities, said senior author Nicola Klein, MD, PhD, director of the Kaiser Permanente Vaccine Study Center. “This study highlights that access to both preventive methods results in large numbers of infants being protected from RSV.”
Vaccine Study Center researchers are also examining the effectiveness of the RSVpreF vaccine and of nirsevimab, and plan to compare the two approaches to see which provides longer protection, Dr. Jacobson said. “It’s nice to see people excited about this as a way to reduce illness in infants,” she said.
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