Moderna’s mRNA-Based RSV Vaccine Just Passed a Major Test

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Moderna has become a well-known name thanks to its highly effective COVID-19 vaccine, based on mRNA technology. But even before the pandemic hit, the company was developing an mRNA-based vaccine against another scourge, respiratory syncytial virus (RSV), which primarily affects infants and the elderly. In a release issued on Jan. 17, the Massachusetts-based company said an early look at data from the late-stage trial of its RSV vaccine shows that the shot is effective.

Among 37,000 people over age 60 in 22 countries, the vaccine was 83.7% effective in reducing moderate RSV illness, defined as two or more symptoms of the disease, and 82.4% effective in reducing more severe illness encompassing three or more symptoms compared to those receiving placebo. As RSV progresses, people move from cold-like symptoms to more severe respiratory distress and damage, including wheezing, difficulty breathing, and inflammation of the lungs. The trial is ongoing, but based on the positive results, Moderna plans to file a request for approval of the vaccine from the Food and Drug Administration (FDA) this year.

In doing so, Moderna would join Pfizer, which submitted a request for expedited review of its RSV vaccine for older adults last December. The company reported results similar to Moderna’s—it was 86% effective in reducing severe respiratory illness. Pfizer is also developing a RSV vaccine for pregnant women, who would be immunized to protect their newborns after delivery.

Dr. Paul Burton, chief medical officer at Moderna, says that the company’s experience in developing the COVID-19 mRNA vaccine played a “huge” role in the development of the RSV shot. “MRNA as a platform is predictable, synthesizeable, and has high fidelity,” he says. “The pandemic did a couple of things: It helped us to understand the importance of respiratory viruses and how we can protect against them, and provided a platform that has been tried and tested in an unprecedented number of people, which gives us extraordinary confidence [in the safety and effectiveness of the vaccine].”

Each year, 58,000 to 80,000 children under age five are hospitalized for RSV in the U.S., including many premature infants, who are at highest risk for the respiratory illness. Some 100 to 300 children die from the infection. Among adults over age 65, there are 60,000 to 120,000 hospitalizations each year, and 6,000 to 10,000 deaths.

During the 2022-2023 winter season, rates of RSV, along with the seasonal flu, began climbing early in the fall, as children shielded from infections during the COVID-19 pandemic by lockdowns and remote learning returned to school and were exposed to RSV for the first time. By late December, monthly RSV cases in the U.S. peaked at about 19,500 cases.

Burton says the company has five additional trials ongoing involving the RSV vaccine, including in young children and pregnant women. They are also testing the RSV shot in combination with other vaccines, such as influenza and COVID-19. “Our ambition is to bring two to three vaccines together into a single shot to provide broad protection against all sorts of different respiratory viruses,” he says. “The advantage in compliance and adherence would be extremely powerful.”

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