Respiratory Syncytial Virus (RSV) is a common respiratory pathogen that typically causes mild, cold-like symptoms. While often associated with severe illness in infants and young children, RSV can also lead to significant health complications in adults. The recent development and approval of vaccines for adults represents a major advancement, offering a new defense against a virus previously without specific preventative measures for older individuals.
Understanding RSV: A Threat to Adults
RSV spreads through respiratory droplets when an infected person coughs or sneezes, and it can also live on surfaces for several hours. Common symptoms in adults include runny nose, cough, sneezing, sore throat, and headache, often resembling a common cold. However, the virus can progress to more serious conditions like pneumonia or bronchiolitis, an inflammation of the small airways.
Certain adult populations face a higher risk of severe RSV disease. These include older adults and individuals with underlying medical conditions. Chronic lung diseases such as asthma or chronic obstructive pulmonary disease (COPD), heart disease, and weakened immune systems due to illness or medication can increase susceptibility to severe outcomes. For these vulnerable groups, RSV infection can lead to hospitalization, exacerbation of existing conditions, and even death.
Breakthroughs in RSV Vaccine Development
The scientific journey toward an RSV vaccine for adults involved research, focusing on a specific viral component known as the fusion (F) protein. This protein is present on the surface of the virus and undergoes a significant shape change, from a prefusion to a postfusion state, when it prepares to infect cells. Researchers discovered that antibodies targeting the prefusion form of the F protein are effective at neutralizing the virus and preventing infection. This insight was key for vaccine development.
Clinical trials for adult RSV vaccines demonstrated substantial efficacy in preventing lower respiratory tract disease caused by RSV. Studies showed that vaccines targeting the prefusion F protein provided strong protection against symptomatic RSV infection and severe outcomes in older adults. These trials involved thousands of participants, evaluating the vaccine’s ability to reduce the incidence of medically attended RSV-associated lower respiratory tract disease and hospitalization. The observed efficacy rates, often exceeding 80% for severe disease, provided strong evidence supporting the vaccines’ effectiveness and led to regulatory approvals.
Approved RSV Vaccines and Recommendations
Currently, three RSV vaccines are approved and available for adults: Arexvy by GSK, Abrysvo by Pfizer, and mResvia by Moderna. Arexvy and Abrysvo are approved for adults aged 60 years and older. Abrysvo also has an expanded indication for adults aged 18 to 59 years who are at increased risk for RSV-associated lower respiratory tract disease.
Health organizations, such as the Centers for Disease Control and Prevention (CDC), guide the use of these vaccines. The CDC recommends a single dose of any RSV vaccine for all adults aged 75 and older, and for adults aged 50–74 who have an increased risk of severe RSV disease. Abrysvo is also approved for pregnant individuals between 32 and 36 weeks gestation to provide passive immunity to their newborns, protecting infants from birth up to six months of age. These vaccines are not currently recommended annually, with ongoing surveillance to determine the need for future doses.
Safety Profile of RSV Vaccines
Clinical trials and monitoring have provided data on the safety profile of the approved RSV vaccines. The most frequently reported side effects are generally mild to moderate and temporary. These reactions commonly include pain, redness, or swelling at the injection site, which typically resolve within a day or two.
Other common systemic side effects include fatigue, headache, and muscle pain. Serious adverse events are rare, with studies indicating that the benefits of preventing severe RSV infection, hospitalization, and death in recommended populations generally outweigh the potential risks. Post-marketing surveillance continues to monitor for any less common or delayed side effects, ensuring the vaccines remain safe for widespread use.