Pfizer adult RSV vaccine efficacy declines slightly after 18 months

PfizerA vaccine that protects adults 60 and older against respiratory syncytial virus was somewhat less effective after 18 months, according to clinical trial results the company announced Wednesday.

Data from New York-based Pfizer Clinical trial on more than 34,000 seniors over two RSV seasons, or 24 months. The most recent data is for participants in the Northern Hemisphere in Mid-Season 2 trialabout 18 months after vaccination.

The shot was 78.6% effective against more severe lower respiratory tract disease with three or more symptoms after 18 months, a slight decrease from 85.7% in one year. These symptoms include wheezing, shortness of breath, rapid and shallow breathing, and mucus production.

The vaccine was about 49% effective against the same condition with two or more symptoms occurring 18 months later, according to Pfizer. This is a sharp drop from the shot’s 66.7% effectiveness in one year.

The vaccine was generally well tolerated, and no adverse events were reported by participants at the 18-month mark.

Pfizer provided the results to advisory committee From the Centers for Disease Control and Prevention on Wednesday. The committee will form a recommendation on when and how often the company’s RSV shot should be administered in the United States now that the FDA has approved the vaccine.

Pfizer’s RSV vaccine is the second to receive approval, after a shot of it GlaxoSmithKlinewhich will provide similar long-term data on Wednesday.

Pfizer’s findings are the first glimpse of its vaccine’s ruggedness in protecting against respiratory syncytial virus, which causes mild, cold-like symptoms in most people but causes more severe infections in the elderly and children.

The data suggests that the protection provided by the vaccine slowly wanes over time, similar to what has been seen with covid and influenza shots.

But the 18-month data also indicates that the Pfizer shot still protects overall against respiratory syncytial virus after one year.

It’s still not clear what the vaccine’s efficacy will look like after 24 months. Pfizer expects to release this data later this year, which should provide a better picture of shot durability.

Annaliesa Anderson, Pfizer’s head of vaccine research and development, told CNBC that the data from the Phase 3 clinical trial is “very encouraging.”

She indicated that the vaccine maintained its high efficacy against lower respiratory tract diseases with three or more symptoms, which are more severe than the same condition with two or more symptoms.

“As with most vaccines, you’re really looking for an effect against the more serious disease that causes higher levels of mortality, morbidity, and healthcare-related contact,” Anderson told CNBC. “Being able to see continued high efficacy is very important to us, and we think it will provide people with relief while they take the vaccine.”

Pfizer has not released data on the effectiveness of its vaccine against severe RSV disease defined as a patient requiring hospitalization, oxygen support, or a ventilator.

Studies are ongoing, Anderson said, as is research evaluating the vaccine’s effectiveness in older adults with weakened immune systems.

RSV kills 6,000 to 10,000 elderly people and takes 60,000 to 160,000 of them each year, according to the CDC.

The risk of hospitalization increases with age, and adults age 70 or older are at greatest risk.

Pfizer estimates that if 50% of people 60 and older received its shot for seniors, the vaccine could prevent more than 5,000 deaths, 68,000 hospitalizations, 51,000 emergency department visits and more than 422,000 outpatient visits.