Respiratory Syncytial Virus (RSV) is a widespread respiratory illness that affects the lungs and breathing passages. It causes mild, cold-like symptoms for most healthy individuals, often resolving within a week or two. However, RSV can lead to more severe outcomes, particularly for certain vulnerable groups. The development of RSVPreF vaccines helps prevent serious illness caused by this common virus.
Understanding RSV
RSV is a respiratory virus that infects the nose, throat, and lungs. It spreads easily from person to person through respiratory droplets when an infected individual coughs or sneezes, or through direct contact with contaminated surfaces. Symptoms appear about four to six days after infection and can include a runny nose, cough, sneezing, fever, decreased appetite, and wheezing.
While most individuals experience mild symptoms, RSV can cause serious lung infections such as bronchiolitis, an inflammation of the small airways, and pneumonia. Infants, especially those younger than six months, and older adults, particularly those over 65, are at a higher risk of developing severe RSV and requiring hospitalization. In the U.S., RSV is a leading cause of hospitalization for children under one year old, and it is estimated to cause thousands of deaths annually in adults over 65.
How the RSVPreF Vaccine Protects
The RSVPreF vaccine targets the virus’s fusion (F) protein. This protein is located on the surface of RSV and is responsible for the virus’s ability to enter and infect human cells. The F protein exists in two main forms: a pre-fusion state and a post-fusion state. The pre-fusion form is the shape the protein takes before it fuses with a host cell and is highly effective at triggering a strong immune response.
However, the pre-fusion F protein is naturally unstable and tends to change into the more stable post-fusion form. The RSVPreF vaccine stabilizes this pre-fusion F protein by introducing specific modifications. This ensures the F protein remains in its pre-fusion shape, preventing it from transitioning to the less immunogenic post-fusion state. When introduced into the body, this stabilized protein prompts the immune system to produce a high level of neutralizing antibodies. These antibodies then bind to the RSV virus, blocking its ability to fuse with and infect cells, thereby preventing illness.
Recommended Vaccination Groups
RSVPreF vaccines are approved and recommended for specific populations to protect against severe RSV disease. Two widely available vaccines, Arexvy and Abrysvo, along with the newer mResvia, target different groups based on their risk of severe outcomes. These recommendations are guided by public health bodies like the Centers for Disease Control and Prevention (CDC) and ACIP.
Arexvy is indicated for adults aged 60 and older, and is also approved for adults aged 50 through 59 with increased risk factors for lower respiratory tract disease caused by RSV. These risk factors include underlying medical conditions such as chronic obstructive pulmonary disease (COPD), asthma, heart failure, and diabetes, which can worsen with an RSV infection. Abrysvo is approved for adults aged 60 and older. It is also approved for use in pregnant individuals between 32 and 36 weeks of gestation. This maternal vaccination aims to protect their infants from RSV-associated lower respiratory tract disease from birth through six months of age by transferring protective antibodies across the placenta.
The mResvia vaccine, an mRNA-based option, is approved for adults aged 60 and older. It is also approved for individuals aged 18 through 59 who are at increased risk for lower respiratory tract disease caused by RSV. For older adults, a single dose of an RSV vaccine is recommended, with no specific brand preference between Arexvy, Abrysvo, or mResvia. Vaccination is suggested before the start of the RSV season (fall through spring).
Effectiveness and Safety Information
Clinical trials and real-world data demonstrate the effectiveness of RSVPreF vaccines in reducing severe outcomes. For adults aged 60 and older, the vaccines have shown approximately 75% effectiveness against RSV-associated acute respiratory infection, emergency department visits, or hospitalization. Studies show an initial efficacy of around 82.6% in the first year, with protection remaining substantial at 62.9% over three seasons for older adult vaccines. Among immunocompromised patients, vaccine effectiveness has ranged from 67.0% to 73.1%.
For pregnant individuals who receive the Abrysvo vaccine between 32 and 36 weeks of gestation, studies show a significant reduction in severe RSV-related lower respiratory tract disease in their infants. The vaccine reduced the risk of severe lower respiratory tract disease by 91.1% within 90 days after birth and by 76.5% within 180 days after birth. The risk of hospitalization for RSV in infants was also reduced by 68% within three months and 57% within six months after birth.
Regarding safety, common side effects across RSV vaccines include injection site reactions such as pain, swelling, or redness, as well as fatigue, headache, and muscle aches. These reactions are mild and temporary. Rare, serious adverse events have been reported. Guillain-Barré syndrome, a condition affecting the nerves, has been noted in very rare cases in older adults who received an RSV vaccine, with an estimated excess of 5.2 to 18.2 cases per million doses. However, the overall risk is considered lower than the risk of severe RSV infection.
For pregnant individuals, an increased rate of preterm birth was observed in some initial clinical trials for the Abrysvo vaccine; however, newer real-world studies have not found a statistically significant difference in preterm birth rates between vaccinated and unvaccinated women. To mitigate this potential risk, the vaccine is specifically recommended for administration at 32 through 36 weeks of gestation.