Well-Being Prevention & Cures

Pfizer’s RSV vaccine candidate safe and effective in older adults

The company is nearing the end of phase 3 clinical trials for RSVpreF that could help prevent hospitalizations and deaths from respiratory syncytial virus.
front of building with Pfizer sign above doors
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Story at a glance


  • RSV stands for respiratory syncytial virus, a common virus that causes cold-like symptoms.

  • However, it can cause serious illness in infants and older adults, like when it develops into bronchiolitis and pneumonia.

  • Pfizer’s vaccine candidate for RSV is more than 85 percent effective at preventing severe illness in older adults, according to preliminary results.

Respiratory syncytial virus, or RSV, is a group of viruses that cause cold-like symptoms, including runny nose, coughing and sneezing. When it causes severe illness, it can lead to bronchiolitis (inflammation in the small airways in the lungs) or pneumonia (infection in the lungs), in children under the age of 1, according to the Centers for Disease Control and Prevention. There are a few companies working on RSV vaccine candidates, and Pfizer in particular has announced results from their phase 3 clinical trials of their version called RSVpreF.

Pfizer announced that their new RSV vaccine candidate is more than 85 percent effective in preventing severe lower respiratory tract illness in older adults, according to a statement on the company’s website. They define severe illness as three or more symptoms. The vaccine candidate is more than 66 percent effective at preventing illness overall, defined as two or more symptoms. The company tested this vaccine candidate in about 37,000 people ages 60 and older and are looking to recruit a total of 40,000. 

Importantly, it targets the two main strains of the virus, giving broader protection.

“We are delighted that this first bivalent RSV vaccine candidate, RSVpreF, was demonstrated to be efficacious in our clinical trial against this disease, which is associated with high levels of morbidity and mortality in older adults,” said Annaliesa Anderson, who is the senior vice president and chief scientific officer for vaccine research and development at Pfizer, in the statement. 

This vaccine could help a lot of people. Worldwide, RSV is suggested to be the reason for hospitalizations of 336,000 older adults each year, resulting in 14,000 deaths, according to a study from 2020.

“Scientists and researchers have worked to develop RSV vaccines with little success for over half a century,” Anderson said in the statement. “These findings are an important step in our effort to help protect against RSV disease, and we look forward to working with the FDA and other regulatory agencies to make this vaccine candidate available to help address the substantial burden of RSV disease in older adults.”