PfizerThe vaccine, which protects adults aged 60 and over from respiratory syncytial virus, was slightly less effective after 18 months, according to clinical trial results the company announced on Wednesday.
The data comes from New York-based Pfizer’s clinical study of more than 34,000 older adults over two seasons of RSV. The most recent data are specific to participants in the northern hemisphere at the “mid-season” of the study, approximately 18 months post-vaccination.
For more severe lower respiratory tract disease with three or more symptoms, vaccination was 78.6% effective by the middle of Season 2, down slightly from 85.7% by the end of Season 1. These symptoms include wheezing, shortness of breath, rapid and shallow breathing, and mucus production.
According to Pfizer, the vaccine was about 49% effective against the same disease with two or more symptoms by the middle of season two. That’s a steeper drop from the shot’s effectiveness of 66.7% over a season.
The vaccine was generally well tolerated, and participants reported no adverse events through the middle of season two.
Pfizer presented the findings to an advisory committee at the Centers for Disease Control and Prevention on Wednesday. The committee will develop a recommendation on how often the company’s RSV vaccine should be administered in the United States, such as whether vaccination should be annual.
The consultants also recommend vaccination for a certain age group.
Pfizer’s RSV vaccine is the second, following a vaccination, to receive Food and Drug Administration approval GlaxoSmithKlinewhich will release similar longer-term data on Wednesday.
Pfizer’s results provide a first look at the vaccine’s durability in protecting against RSV, which causes mild cold symptoms in most people but more severe infections in older adults and children.
The data suggests that the protection offered by the vaccine is slowly eroding over time, similar to what is seen with vaccines against Covid and flu.
But mid-season data also suggests that Pfizer’s vaccine is still generally protective against RSV at one year.
It is still unclear what the effectiveness of the vaccine will be over two full seasons. Pfizer expects to release that data later this year, which will provide a better picture of the shot’s durability.
Annaliesa Anderson, Pfizer’s director of vaccine research and development, told CNBC that the company was “very encouraged” by the data from the Phase 3 clinical trial.
She noted that the vaccine maintains high efficacy against lower respiratory diseases with three or more symptoms that are more severe than the same disease with two or more symptoms.
“As with most vaccines, the primary concern is efficacy against more serious diseases that result in higher mortality, morbidity and exposure to healthcare,” Anderson told CNBC. “It’s very important for us to be able to continue to see the high level of efficacy and we believe it will bring comfort to people as they take the vaccine.”
Pfizer has not released data on the effectiveness of its vaccine against severe RSV disease, which is patients who require hospitalization, oxygen support, or a mechanical ventilator.
Anderson said studies are ongoing, as well as research to evaluate the vaccine’s effectiveness in older adults with compromised immune systems.
According to the CDC, RSV kills 6,000 to 10,000 older adults each year and 60,000 to 160,000 of them are hospitalized.
The risk of hospitalization increases with age, and adults 70 and older are more susceptible.
Pfizer estimates that the vaccine could prevent more than 5,000 deaths, 68,000 hospitalizations, 51,000 emergency room visits and more than 422,000 outpatient visits if 50% of people age 60 and older received the older-adult vaccine.
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