Pfizer's RSV Shot Cut Hospital and ER Visits 60 Percent in Year Three. For Lung Disease, the Range Includes Zero.

One dose of Pfizer's RSV vaccine, Abrysvo, still cut hospital and emergency room visits for acute respiratory illness by an estimated 60 percent in the third RSV season after the shot. That figure comes from a Kaiser Permanente Southern California study of adults 60 and older, published September 18 in Infectious Diseases and Therapy. The authors say no real-world estimate beyond the second season had been published before it.

What is actually known is narrower than the headline number. Protection was highest in the first season and lower in each one after. For a second outcome, lower respiratory tract disease, the third-season estimate was 51 percent, but its range runs from 12 percent below zero to 78 percent. The data cannot rule out no protection at all for that outcome. The evidence on the first outcome is firmer. The evidence on the second is thin.

What the Kaiser team measured

Sara Tartof's group at the health system's Department of Research and Evaluation in Pasadena ran a test-negative case-control study. In that design, researchers compare vaccination history in people who tested positive for RSV with people who sought care for similar symptoms but tested negative. The cases here were RSV-positive patients without a coinfection. The controls tested negative for RSV, human metapneumovirus, influenza and COVID-19, and positive for some other germ that no vaccine targets.

The study window ran from November 24, 2023 to April 18, 2026, which covers three RSV seasons. Vaccination counted if it happened at least 21 days before illness. The study population, adults 60 and older in one California health system, has a high rate of other medical conditions, as the abstract notes. The study is observational and retrospective, so it cannot show the vaccine caused the difference, only that vaccinated people were less often among the RSV cases.

Season by season

• Acute respiratory illness, season one: 81 percent (95% CI 71 to 87). Season two: 64 percent (48 to 75). Season three: 60 percent (15 to 81).
• Lower respiratory tract disease, season one: 80 percent (68 to 87). Season two: 70 percent (53 to 81). Season three: 51 percent (-12 to 78).
• Across all three seasons combined, protection was 73 percent for both outcomes, with ranges of 64 to 80 and 65 to 79.

The third-season ranges are wide. The authors describe the result for acute respiratory illness as more definitive, and the lung disease result as imprecise because of limited event numbers. Their conclusion is that the vaccine protects for at least three seasons. That reading holds for the first outcome, where the range stays above zero. For the second, the interval crosses it.

A different study, a similar slope

A separate US analysis points the same direction. A US hospital network tracked 6,958 adults 60 and older across 26 hospitals in 20 states over two seasons and reported in JAMA that effectiveness against RSV hospitalization was 69 percent in the same season as the shot and 48 percent in the prior season (95% CI 27 to 63, P = .06). That analysis counted any RSV vaccine rather than Abrysvo alone. It also found lower protection in immunocompromised adults, 30 percent with a range from -9 to 55, versus 67 percent in immunocompetent adults.

The two studies use different hospitals, different vaccines and different definitions of the outcome, and they still show a drop after year one. Neither tells a reader whether a booster would restore protection. The JAMA authors say monitoring is still needed to find the best revaccination interval.

Who paid, and what the guidance says now

Publisher metadata for the Kaiser paper lists Pfizer as the funder. Pfizer makes Abrysvo, so the company that sells the vaccine paid for the study of how long it lasts. That does not make the numbers wrong, and the paper reports its wide intervals openly. It is a reason to read the third-season conclusion alongside independent data as it arrives. This report did not have access to the paper's full text, which sits behind a bot block at the publisher, so details such as case counts and the authors' own disclosure statement were not reviewed. The figures above come from the abstract.

The CDC currently recommends a single RSV vaccine dose for all adults 75 and older and for adults 50 to 74 at increased risk of severe illness. Its guidance page, last reviewed February 24, 2026, says the vaccine is not an annual shot and that the need for further doses will be evaluated by its advisory committee later. The Kaiser data arrive after that review date and do not change the written recommendation.

I did not find a published comparison of third-season RSV protection from another vaccine maker or another health system, so there is nothing yet to measure the 60 percent against. Replication has not happened.