RSV Vaccine During Pregnancy

Respiratory syncytial virus (RSV) is a common respiratory virus that usually causes mild cold-like symptoms. Most people recover in a week or two, but RSV can be a serious illness for some groups, particularly infants and older adults.

Respiratory syncytial virus is one of the most common causes of childhood respiratory illness and results in annual outbreaks of respiratory illnesses in all age groups. An estimated 58,000–80,000 children under age 5 years, most of them infants under age 6 months, are hospitalized each year nationwide because of RSV infection, with some requiring oxygen, intravenous fluids, or mechanical ventilation. Each year, an estimated 100–300 children younger than age 5 years die because of RSV in the US.

RSV epidemics in the Northern Hemisphere typically occur between October and April, peaking in December or January. The COVID-19 pandemic disrupted this predictable timing for RSV season, but pre-pandemic seasonal patterns are returning.

Both of the new RSV vaccines are based on a traditional vaccine platform, using a lab-created (recombinant) version of the virus’ protein that is necessary for RSV to enter and infect the cells in the lower respiratory tract. This protein triggers the body to produce specific antibodies that prevent infection from occurring. This is the same method that has been used safely for decades to create the established and routinely administered vaccines against hepatitis B, pneumonia, and meningococcal infections.

On August 21, 2023, the U.S. Food and Drug Administration (FDA) approved the first RSV vaccine, Abrysvo (Pfizer), for use in pregnant individuals to protect newborns and infants against severe RSV disease in the first 6 months after birth. It’s important to know that although 2 different RSV vaccines were approved for use in older adults (over age 60), ONLY the Abryso (Pfizer) vaccine was approved for use in pregnancy.

Next, on September 22, 2023, the CDC’s Advisory Committee on Immunization Practices (ACIP) voted to approve and recommend a single dose of this RSV vaccine for pregnant people who are between 32 through 36 completed weeks of pregnancy (this standard dating language means that you can receive the vaccine up until the 1^st day of your 37^th week). Getting the vaccine earlier in this window is ideal, since it takes at least 2 weeks for your body to respond to it by producing antibodies at high enough levels to pass to the fetus and protect the newborn after delivery.

The American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal Fetal Medicine (SMFM) both leading national organizations representing specialists in obstetric care, have also strongly endorsed RSV vaccination during pregnancy. Similar to seasonal influenza vaccination, RSV vaccination is recommended for pregnant individuals who will be delivering during RSV season.  

The Abrysvo vaccine has been shown in large studies that compared vaccines against placebo to produce antibodies against RSV that pass to your fetus. This means the baby will have antibodies in their system to protect them against getting RSV for the first 6 months after birth when their risk of severe illness is highest.

Among all 7,000 pregnant individuals who were randomly divided to receive vaccine or placebo between 24-36 weeks, Abrysvo reduced the risk of severe illness in infants by 81.8% in the first 3 months after birth, and 69.4% within the 6 months after birth. When the vaccine was studied for those people who received it between 32-36 weeks (about 3000 people), the benefit was not significantly different. The risk of severe illness was reduced by 91% within 3 months after birth when compared to placebo. Within 6 months after birth, Abrysvo reduced the risk of any lower respiratory illness in infants by 57% and by 76% for severe illness, when compared to placebo.

The prescribing information for Abrysvo does include a statement addressing the fact that a small imbalance in preterm births was seen in Abrysvo recipients (5.7%) compared to those who received placebo (4.7%), which, while higher, was not thought to be clinically significant. This imbalance was only seen in trial participants residing in lower-to-middle-income countries. This statement was included to be completely transparent, though it is strongly felt that the available data are insufficient to establish a cause-and-effect relationship between preterm birth and Abrysvo. However, out of an abundance of caution, the statement informs healthcare professionals that to minimize the theoretical risk of preterm birth following administration of RSV vaccine before 32 weeks of gestation, Abrysvo should be administered in pregnant individuals during the currently recommended window of 32 through 36 completed weeks of gestation.

Common side effects that were seen more frequently in pregnant people who received the Abryvso RSV vaccine were localized, not body-wide, and included pain at the site of injection, headache, and muscle pain (myalgia), similar to vaccine side effects seen with other vaccines, including those against influenza.

Centers for Disease Control and Prevention (CDC)

American College of Obstetricians and Gynecologists (ACOG)