RSV Shot During Pregnancy Benefits Baby, Trial Shows

pregnant woman in white dress wearing bandage

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Key Takeaways

  • Pfizer earned a breakthrough therapy designation status for an RSV vaccine for pregnant people to help protect infants against severe RSV illness in their first year of life. 
  • Phase 2 clinical trial results show that the RSVpreF vaccine is effective at providing fetal antibodies. It will now move to phase 3 trials.
  • RSV is a common seasonal virus that can cause bronchitis and pneumonia in infants, children, and older adults who are at high risk for severe respiratory illness.
  • There is currently no vaccine to prevent RSV.

Early results of a phase 2 clinical trial show Pfizer’s investigational RSVpreF vaccine provides newborns antibody protection against RSV. RSV—respiratory syncytial virus—is a common cause of infant hospitalization and childhood pneumonia for an estimated 58,000 children under the age of 5 each year. 

The placebo controlled study, which was funded by Pfizer, included 406 women ranging from 24 to 36 weeks of pregnancy. By the time the 80% of participants who received the vaccine delivered their babies, both maternal and umbilical cord blood were positive for both RSV antibodies. This means infants were born with a layer of protection against a future RSV infection.

“If approved by the FDA, this maternal immunization has the potential to be the first vaccine candidate to help protect infants in their vulnerable first months of life from disease caused by this highly-contagious virus,” Kathrin U. Jansen, PhD, senior vice president and head of vaccine research & development at Pfizer, said in a press release.

What Is RSV and Who Is at Risk?

RSV is a common contagious respiratory virus that circulates each year similar to influenza. It’s a major cause of acute lower respiratory tract infection (bronchitis, pneumonia) hospitalizations for infants and children younger than 5 years old.

There is not currently a vaccine to prevent RSV. 

According to the Centers for Disease Control and Prevention (CDC), almost all children will have an RSV infection by their second birthday.

Symptoms of RSV typically occur in stages and include:

  • Fever
  • Decreased appetite
  • Cough
  • Sneezing
  • Wheezing
  • Runny nose

While the majority of children infected with RSV will have mild symptoms and make a complete recovery, there is a subset of infants, children, and older adults who are at a high risk for serious RSV complications resulting in hospitalization, and possibly, death. 

Infants and children with specific risk factors are more susceptible to severe RSV illness. These groups include:

  • Premature infants
  • Infants less than 6 months old
  • Children with chronic lung disease
  • Children with congenital heart disease
  • Children with weakened immune systems
  • Children with neuromuscular disorders
  • Children who have difficulty swallowing 

How RSV Is Currently Treated 

Most children with an RSV infection recover on their own. However, for infants and children at high risk for serious complications, there is a medication approved by the U.S. Food and Drug Administration (FDA) called Synagis (palivizumab) used to prevent hospitalization for high risk children.

Palivizumab is a monthly injection for premature infants (delivered at or before 35 weeks) and babies with a pre-existing condition that puts them at risk for hospitalization and severe illness from an RSV infection. It’s only administered during RSV season (fall, winter, and spring).

An RSV Vaccine Is in the Works

In addition to the RSVpreF vaccine for pregnant people, scientists are also exploring an RSV vaccine for all infants and small children. Phase 3 clinical trials of nirsevimab, developed by Sanofi and AstraZeneca, show the shot is 74.5% effective at preventing the virus in both healthy and high risk infants.

Moderna is also in the process of testing a single dose RSV vaccination for adults over the age of 60. Currently called mRNA-1345, the vaccine is in phase 3 of clinical trials. Researchers hopes it will help prevent over 177,000 hospitalizations and 14,000 deaths associated with RSV complications in people over 65.

What’s Next?

The RSVpreF vaccine for pregnant people will move into phase 3 of clinical trials to establish if it is safe without the chemical compound aluminum hydroxide, which was associated with local reactions and side effects in earlier phases of the study.

Currently, the immunizations recommended for pregnant people include the annual influenza vaccine and the Tdap vaccine to prevent neonatal pertussis (whooping cough).

Since clinical trials can take several years to complete, a licensed RSV vaccine for pregnant women is still a ways off. In the meantime, people can help prevent the spread of RSV, which is transferable by air droplets after a person coughs or sneezes, by practicing common safety precautions, including:

  • Washing your hands frequently
  • Covering your cough and sneezes
  • Avoiding crowded spaces
  • Wearing a mask indoors
  • Sanitizing frequently-touched surfaces
  • Staying home if you are sick

If your child is at high risk for severe RSV disease, talk with your healthcare provider to see if Synagis is a preventative option during RSV season.

What This Means For You

RSV is transmissible by air droplets. The best way to stop the spread is to practice good hand hygiene, avoid large crowds, and avoid people who are sick. If you have an infant or young child that is at risk for severe RSV illness, talk with your healthcare provider about additional ways to prevent hospitalization.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Healio. Moms who receive investigational RSV vaccine pass antibodies to infants.

  2. Centers for Disease Control and Prevention. RSV in infants and young children.

  3. Simões EAF, Center KJ, Tita ATN, et al. Prefusion F protein–based respiratory syncytial virus immunization in pregnancy. N Engl J Med. 2022;386(17):1615-1626. doi:10.1056/NEJMoa2106062

  4. Centers for Disease Control and Prevention. Increased interseasonal respiratory syncytial virus (RSV) activity in parts of the southern United States.

  5. Centers for Disease Control and Prevention. RSV symptoms and care.

  6. National Library of Medicine: DailyMed. SYNAGIS- palivizumab injection, solution [drug label].

  7. Hammitt LL, Dagan R, Yuan Y, et al. Nirsevimab for prevention of RSV in healthy late-preterm and term infants. N Engl J Med. 2022;386(9):837-846. doi:10.1056/nejmoa2110275

  8. BioSpace. Moderna initiates phase 3 portion of pivotal trial for mRNA respiratory syncytial virus (RSV) vaccine candidate, following independent safety review of interim data.

  9. Centers for Disease Control and Prevention. RSV in older adults and adults with chronic medical conditions.

  10. Centers for Disease Control and Prevention. Adult immunization schedule by medical condition and other indication.

By Amy Isler, RN, MSN, CSN
Amy Isler, RN, MSN, CSN, is a registered nurse with over six years of patient experience. She is a credentialed school nurse in California.