Jennifer Middleton, MD, MPH
Posted on May 8, 2023
The U.S. Food and Drug Administration (FDA) approved the first respiratory syncytial virus (RSV) vaccine last week. Manufactured by GlaxoSmithKline, Arexvy has been approved for adults 60 years and older. Following review and the issuing of recommendations for use by the U.S. Centers for Disease Control and Prevention (CDC), the vaccine is anticipated to be available this coming fall in the United States. RSV causes only mild upper respiratory infections for most people, but in young children and older adults it can lead to severe disease. The CDC estimates that, in the United States, RSV annually causes between 6,000 and 10,000 deaths in adults older than 65 years.
The FDA approved Arexvy after review of its phase 3 randomized controlled trial (RCT) data in nearly 25,000 adults 60 years and older. The researchers found that:
[V]accine efficacy against RT-PCR–confirmed RSV-related lower respiratory tract disease was 82.6% (96.95% confidence interval [CI], 57.9 to 94.1), with 7 cases (1.0 per 1000 participant-years) in the vaccine group and 40 cases (5.8 per 1000 participant-years) in the placebo group. Vaccine efficacy was 94.1% (95% CI, 62.4 to 99.9) against severe RSV-related lower respiratory tract disease (assessed on the basis of clinical signs or by the investigator) and 71.7% (95% CI, 56.2 to 82.3) against RSV-related acute respiratory infection.
One recipient of the vaccine in this trial did develop Guillain-Barré, and the FDA will require GlaxoSmithKline to monitor the incidence of Guillian-Barré after the vaccine becomes widely available. Pfizer and Moderna are also both working on an RSV vaccine for older adults. Pfizer’s phase 3 data reportedly had two cases of Guillain-Barré, whereas Moderna reported “no safety concerns” with their RCT.
Young children are also adversely affected by RSV, with the CDC estimating between 58,000 and 80,000 hospitalizations a year in the United States. “To protect infants, Pfizer opted to immunize pregnant people a few months before they gave birth.” Pfizer has completed phase 3 trials of this vaccine, and an FDA advisory panel will review this data later this month.
Pfizer may have chosen to vaccinate pregnant people instead of children given the difficult history behind the development of an RSV vaccine, an effort that includes an earlier trial that resulted in harms. “A decade after the virus’s discovery, in 1966, four clinical trials tested an inactivated virus vaccine in children who had never encountered RSV before. To the scientists’ horror, in one of the studies, 80 percent of the vaccinated children were hospitalized when they later contracted the virus itself, and two toddlers—a 14-month-old and a 16-month-old—died.” It wasn’t until 2008 that researchers finally understood why that earlier vaccine failed—the virus’s primary antigen, an F protein, is frustratingly unstable after it fuses with a cell, and that earlier vaccine’s antibodies bonded poorly to live virus but well with dead viruses, “spark[ing] a dangerous cascade of abnormal immune responses.” With this knowledge, researchers could work to identify the structure of the F protein in its prefusion form, and with that structure determined, the race to produce a safe and effective vaccine was off.
If you’d like to read more about RSV, the CDC has information about RSV in older adults and young children, and AFP has a wealth of resources as well. There’s an AFP By Topic on Respiratory Tract Infections that includes these 2017 articles on “Respiratory Syncytial Virus Infection” and “Respiratory Syncytial Virus Bronchiolitis in Children.” These overviews on “Acute Bronchitis,” “Common Questions About Pneumonia in Nursing Home Patients,” and “Pleuritic Chest Pain: Sorting Through the Differential Diagnosis” also mention RSV.
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