This winter more members in Northern California are protecting their babies against a potentially serious winter illness as awareness of a relatively new vaccine becomes more widespread.
While the flu and its vaccine are known, not as many people realize there’s a vaccine against Respiratory Syncytial Virus (RSV), specifically given during pregnancy.
In 2023, the U.S. Food and Drug Administration approved the first RSV vaccine, Abrysvo, for use during pregnancy. Physicians across the United States, including those at Kaiser Permanente, have since urged their patients to get this single-dose vaccine.
To receive the vaccine, people must be between 32 and 36 weeks of pregnancy in the fall and winter through January. It’s given during that time frame to best protect against RSV when it’s most active.
While the virus causes mild, cold-like symptoms for adults, it can be particularly dangerous for infants. Two to three out of every 100 infants under 6 months are hospitalized with RSV every year, according to the Centers for Disease Control and Prevention. Like flu, RSV circulates between October and March.
“These types of viruses, if they get into the pulmonary tract of infants, can make babies sick and cause them to have a lot of trouble breathing,” said Maureen Cho, MD, a Kaiser Permanente San Rafael ob-gyn. “Infants do not have robust immune systems, so they cannot fight off viruses effectively, which can lead to hospitalizations, and, in rare cases, even death.”
Efforts to increase prenatal vaccinations of RSV have yielded positive results. In the 2024-2025 season, Kaiser Permanente Northern California vaccinated more than 9,000 pregnant patients, which was a 67% increase from 2023-2024 season. Data available through late December of 2025 shows that Kaiser Permanente Northern California administered nearly 7,900 prenatal RSV vaccines since the beginning of September 2025. That’s more than 1,100, or a 17 percent increase, when compared to the tally from the same time period in 2024.
“It is an incredibly important vaccine to be given to our pregnant mothers,” Dr. Cho said. “It is one way for the woman’s body to build immunity and to be able to pass on that immunity to the infant prior to birth.”
Dr. Cho said Abrysvo provides protection from RSV for infants during the first 6 months of their life.
Patients who weren’t 32 to 36 weeks pregnant in the fall or January can still have their baby immunized as an infant with an RSV preventive antibody called Nirsevimab, Dr. Cho added. To get the shot, babies must be younger than 8 months either at the start or during the RSV season.
The vaccine is ‘very safe’
“It has gone through rigorous testing to ensure that there were no harmful effects that would make it dangerous to recommend to the mass population of pregnant women. It is something that is very safe to administer and receive,” Dr. Cho said, adding that the vaccine is effective. “The overall outcome has shown that we have definitely decreased the number of hospitalizations of infants with RSV.”
The prenatal vaccinations, along with the immunizations given to infants, led to an estimated 50% decline in the number of child hospitalizations for RSV at Kaiser Permanente Northern California hospitals last year.
Dr. Cho decided to get the RSV vaccination herself, while pregnant with her third child in November 2023.
She said it gave both her and her family peace of mind heading into RSV season.
“As a mother taking care of a new infant, we always worry a little bit about children getting sick,” Cho said. “We just don’t want to have that type of an outcome if it’s preventable.”
